tubercles, and are termed Asteracanthus, or starry-spine; there are
very large fin-rays of this kind in the Wealden, Purbeck, Oolites, and
Lias.[517]
[517] For particular information on Ichthyodorulites, consult _Poiss.
Foss._ tom. iii. chap. i. About seventy species are enumerated.
The Ichthyodorulites of the _Rays_ have no cavity like those of the
_Sharks_, and are of a depressed form, and more or less flattened; they
are armed with teeth along their exterior margins, and not on the
posterior edge, as in the latter family.
Fossil Teeth of Fishes.--From the durable nature and striking appearance
of many of the fossil teeth of fishes, and their prodigious numbers in
some deposits, they are familiar objects to the collector. By far the
largest proportion of the detached teeth belongs to various species
and genera of that most numerous, and widely distributed family of
voracious fishes, the Sharks. In the Tertiary strata teeth of this
kind occur of a very large size; in the Chalk many species abound,
particularly of the lanceolate and compressed forms, and of the rugous,
mammillated, palatal teeth, commonly termed _palates_. As we pass
to the more ancient formations, teeth of different forms prevail;
and those which approach the recent types are either very rare or
altogether absent. We will select some examples of the different genera
in illustration of this subject; the previous observations on the form
and structure of the recent teeth render but few introductory remarks
necessary.
Fossil Teeth of Sharks.--The fishes of the Shark and Ray families
belong to the _Placoid_ order; the scales in the former consist of
enamelled plates and tubercles, forming a _shagreen_ surface; and in
the dermal integument of the latter they appear as spines and bosses,
irregularly disposed.
Notwithstanding the diversity in appearance of the teeth of Sharks,
they all possess one essential character of structure, namely, a
base, or osseous root of variable form, which is implanted in the
integuments; and a crown, or external portion, which projects into the
mouth, is covered with enamel or compact dentine, and assumes numerous
modifications, by which the fossil genera are characterized. These
teeth are never imbedded in sockets, nor united to the dentary margins
of the jaws; they only adhere to the integuments of the mouth, and the
covering of the maxillæ; they possess, in most of the Sharks, great
mobility. They are generally disposed in rows; the anterior ones,
being first used, fall out, and are replaced by those on the inner
series. New teeth are also continually formed behind those in use, and
advance successively towards the anterior rows as the latter are shed,
and in their turn occupy the front rank. (See Cyclop. Anat. _Art._
Teeth.) An examination of the fossil and recent teeth of Sharks and
Rays proves that the prevailing existing generic types have but few, if
any, representatives in the fossils, except in those which belong to
the Tertiary and Cretaceous formations; while the genera that appear
isolated, as it were, in the present seas have numerous analogues in
the Secondary strata.
The fossil teeth of this family may be divided into two grand
divisions; namely, those which are more or less of a polygonal,
obtusely conical, or depressed form, having a tesselated arrangement in
the mouth; and those of a triangular, lanceolate shape, with cutting,
or serrated edges, disposed in a series of rows on the jaws. The teeth
of the first group (_Cestracionidæ_) have most analogy to those of the
living genus Cestracion (_Port-Jackson Shark_); the second (_Sgualidæ_)
to the Sharks, commonly so called.
The Cestracion is the only living representative of a family of
squaloid fishes of a peculiar type, whose remains occur in almost the
earliest fossiliferous deposits; it inhabits the seas of New Holland
and the southern coasts of China. The jaws of the Cestracion are
relatively very large, and are armed with numerous rows of teeth,
essentially of two kinds; those situated anteriorly, or towards the
front of the mouth, being adapted for seizing and retaining the food,
and the posterior ones for crushing and bruising. The prehensile teeth
are sharp, angular, and pointed: the others are obtuse, polygonal,
enamelled, and disposed in oblique rows along the margins and inner
surface of both jaws; there are sometimes sixty in each jaw (see
_Bd._ ii. pl. xxvii 11. _fig._ A). Fossil teeth of this type are
exceedingly numerous in the Chalk, Lias, &c. but are very seldom found
in juxtaposition; the decomposition of the cartilaginous integuments
in which they are imbedded, having, in most examples, occasioned their
displacement and dispersion; specimens, however, are occasionally
discovered, in which numerous teeth, of various sizes, are disposed in
mosaic, in their natural relative positions.
The extinct forms of this family (_Cestracionidæ_) are known almost
only by their teeth; and according to the shape, structure, and
sculpture of these organs, M. Agassiz has arranged them into several
genera. They occur in most of the fossiliferous deposits.
Cestracion canaliculatus.--The teeth of a fish belonging to the
existing genus have been discovered in the Chalk of Kent; they are
figured and described by Sir P. Egerton in the beautiful work by Mr.
Dixon.[518] This unique specimen consists of a group of thirteen
posterior molar and three or four detached prehensile anterior teeth,
imbedded in a block of chalk about two inches square. The chief
distinction from the teeth of the recent Cestracion is in the presence
of a large medullary canal which traverses the base of each tooth:
hence the specific name.
[518] Dixon’s Fossils of Sussex, &c. p. 365, tab. xxxii. _fig._ 8. From
the t examination of a specimen lately found at Lewes, Sir P. Egerton
has been led to assign to this species the spine formerly described as
_Spinax major_.
Acrodus (_ridge-tooth_) nobilis. _Lign. 189, fig. 4_, _Ly._ p. 275,
_fig._ 307.--In the Lias and Oolite, oblong enamelled teeth, having the
surface of the crown covered with fine radiating grooves and striæ,
are well known to collectors, in many parts of England, by the name of
_fossil leeches_, from a fancied resemblance to a contracted leech.
They belong to an extinct genus of Cestracionts, named _Acrodus_ by
M. Agassiz. The crown of the tooth is enamelled, and covered with
transverse grooves, which diverge from a longitudinal furrow; the
base is in the form of a parallelogram inclined on its inner side.
These teeth were inserted along the jaws in oblique series, their
longitudinal direction corresponding with that of the bones which
supported them; in their natural position, the extremity of a hinder
tooth was enclosed between the two next anterior teeth. A beautiful
group is figured _Bd._ ii. pl. xxvii^_e_.[519]
[519] The microscopical structure of the teeth of _Acrodus_ is well
shown in the "Odontography," pl. xiv. xv., and beautifully illustrates
the relation of dentine to bone.
[Illustration: Lign. 189. Fossil Teeth of Sharks.]
Fig. 1.--Ptychodus Mortoni. (G. A. M.) _Cret._ _New Jersey._
2.--Psammodus cinctus. (_Ag._) _Mt. L._ _Bristol._
3.--Orodus cinctus. (_Ag._) _Mt. L._ _Bristol._
4.--Acrodus nobilis. _Lias._ _Lyme Regis._
Ptychodus (_wrinkle-tooth_). _Pl. VI. fig. 2_; _Lign. 189_, and _Lign.
191_.--The palatal teeth, which occur more or less abundantly in almost
every chalk-pit, and are known by the name of "palates," belong to
several species of the genus Ptychodus. A very common form is figured
_Pl. VI. fig. 2_; and microscopic views of vertical and transverse
sections, as seen by transmitted light, are shown in figs. 2^_b_,
2^_c_. Groups of these teeth, somewhat naturally arranged, and varying
in size and form according to the situations they occupied in the
jaws, are occasionally found: one specimen in the British Museum, and
formerly in my collection, contains more than 120 teeth. In general
they occur in a very perfect state, with the osseous base and enamelled
crown entire. The dorsal rays or spines previously described (p. 577),
are sometimes found with the teeth, and belong to fishes of the same
genus.
These teeth are of an angular form, and more or less square, the crown
is wider than the root, which is obtuse, truncated, and depressed in
the centre; the enamelled part of the tooth is expanded at the edges,
and forms in the centre a flattened or slightly convex mammillary
projection, which is traversed by large, acute, transverse, parallel
ridges. The borders are granulated, and the sides of the projection
marked with deep vertical plicæ or folds; this description particularly
applies to the species named _P. polygurus_, figured in _Plate VI._ Dr.
Buckland has represented a fine group of these teeth, _Bd._ ii. pl.
xxvi′. Another common species (_P. decurrens_) is distinguished from
the former by the connexion between the large furrows on the crown and
the granulations on the expanded border, which diverge from the outer
edge of the large folds to the margin of the enamel.
The microscopic structure of these teeth presents the same congeries of
medullary and calcigerous tubes as those of the recent Cestracion: see
_Plate VI. figs. 2^b, 2^c_.
The teeth of a species of Ptychodus occur in the arenaceous strata
of the Chalk-formation in New Jersey, which possess the essential
characters of the European types, but differ from them in their
configuration; the only specimen I have seen is figured _Lign. 189,
fig. 1_; it was presented to me by Dr. Morton. The enamelled crown
forms a conical projection, traversed by large inosculating ridges,
which radiate from the summit towards the margin.[520]
[520] I have named it _P. Mortoni_, in honour of my distinguished
friend, the eminent American naturalist and physician, Dr. George
Morton, of Philadelphia, by whom it was discovered.
Psammodus[521] (_sandy-tooth_). _Pl. VI. fig. 1_; _Lign. 128, fig.
2_.--To this genus are referred the fossil teeth of the extinct
Cestracionts, which have the crown formed of small vertical tubes,
with the grinding surface more or less smooth, and presenting only a
punctated or sandy appearance.[522] These teeth are generally flat or
slightly convex, and of a square or oblong form; the base is osseous,
and as large as the crown. Two species are figured, _Lign. 189, fig.
2_, and _Pl. VI. fig. 1^a_. A magnified vertical section of the crown,
displaying the medullary canals and radiating calcigerous tubes, is
represented _Pl. VI. fig. 1^b_, and a transverse section, _fig. 1^c_;
they are thin slices of a tooth, _P. porosus_, from the Black Rock
(Mountain Limestone), near Clifton, viewed by transmitted light. The
large, flat, quadrilateral, oblong teeth that abound in the Stonesfield
Slate belong to the _Strophodus magnus_.
[521] See Odontography, pl. xviii. xix.
[522] Ibid. vol. i. p. 59.
There are several kinds of fossil teeth which possess the same
essential structure as those of Psammodus, but differ in their
external characters; these are referred to other genera by M. Agassiz.
Thus Orodus, _Lign. 189, fig. 3_, comprises those elongated teeth
in which the centre of the crown forms an obtuse transverse cone,
traversed by a ridge from which oblique furrows diverge transversely
towards the circumference. Similar teeth, but with a smooth, obtusely
conical crown, are referred to the genus Helodus. Those with the
crown compressed and elevated, with a sharp edge, and with the base
surrounded by concentric folds, constitute the type of Chomatodes.
A similar crown, but subdivided by deep transverse ridges into
dentations, characterises the genus Ctenoptychius.
Ceratodus (_horn-tooth_) emarginatus. _Lign. 194, fig. 1._--Very
curious dental organs, possessing a structure analogous to that of
the teeth of Psammodus, are found in the Bone-bed of the Lias; they
consist of consolidated plates instead of separate teeth; there was
probably but one plate on each side the jaws. The upper margin is
generally undulated, and more or less worn by use. These dental plates
are composed of two distinct layers; the lowermost portion, or root, is
an osseous, reticulated tissue, as in cartilaginous fishes in general;
and the upper consists of dentine, with minute parallel vertical tubes,
as in Psammodus; these tubes are a continuation of the medullary tissue
of the osseous root.
One species occurs in the Great Oolite at Stonesfield, and very many
forms abound in the Bone-bed at Aust Cliff, near Westbury on Avon: and
in the Trias (bone-bed) of Germany the teeth of several species of
Ceratodus are very abundant.
The fishes to which these fossil teeth, referred to _Ceratodus_,
belonged were most probably Cestracionts; the ray-spine known as
_Nemacanthus_ is provisionally assigned to them.
Edaphodon. _Lign. 190_ and _Lign. 191_, _Ly._ p. 276, _fig._ 309.--The
Chimæroid fishes, though formerly placed with the Plagiostomes (Sharks
and Bays), constitute a distinct group, of which there are but two
recent genera, though several occur in a fossil state. Their dental
organs are very peculiar. Their mandibles are furnished with two
or more pairs of oblong teeth, composed of long hollow cylindrical
columns, placed nearly at right angles to the grinding surface, which
is pitted with minute depressions. These teeth are never shed, but are
persistent, and grow on through life, as in the Rodentia, exhibiting in
this respect a striking contrast with those of the Sharks, which are
feeble and numerous, and constantly replaced by rows of successional
teeth.
Fossil teeth of several species, some much larger than the recent,
have been found in the Tertiary, Cretaceous, and Oolitic deposits. The
first British specimen was discovered in the Chalk-marl at Hamsey, in
1820, by myself; but its nature was not suspected until more perfect
examples were obtained from the Kimmeridge Clay at Shotover by Sir
P. Egerton, and were submitted to Dr. Buckland, who subsequently
ascertained their characters and relations by an examination of
the dental organs of a recent _Chimæra_ in the Museum at Leyden in
1835.[523]
[523] Proceedings of the Geological Society of London, vol. ii. p. 209.
[Illustration: Lign. 190. Mandible of Edaphodon Mantelli.
_Chalk._ _Lewes._ (1/2 _nat. size_.)]
[Illustration: Lign. 191. Edaphodon leptognathus. 1/2 _nat._
_London Clay._ _Bracklesham._
The Upper and Lower Mandibles of the left side; viewed mesially or
from within.
Fig. 1.--The Upper Jaw; left ramus.
_p m._--The premaxillary bone.
1, 2, 3.--The three dental tubercles.
Fig. 2.--The Lower Jaw.
_s._--The symphysial surface, by which this ramus is united
to the opposite or right side of the jaw.
4, 5, 6.--The three dental tubercles, or triturating surfaces,
of the left ramus of the lower jaw.
]
Many specimens, both of the upper and lower mandibles, have since
been discovered in the Eocene beds, Chalk, Upper Greensand, Galt,
Kimmeridge Clay, and Stonesfield Slate. The subject has been carefully
investigated by Sir P. Egerton; and this eminent Ichthyologist has
tabulated the principal forms, and arranged them under five genera.[524]
[524] Viz. Ganodus, Ischyodus, Edaphodon, Elasmodus, and Psaliodus. See
Quart. Journ. Geol. Soc. vol. iii. p. 35; and Dixon’s Foss. Sussex.
In some species the external vertical wall of the plate is formed of
hard dentine, resembling enamel; in others the dentine is disposed
in isolated ramifications, producing a dendritical appearance; the
modifications of this structure occasion the differences observable
in the dental plates of the various species. In some, compact dentine
with parallel canals constitutes the mass of the tooth; in others, the
squamous dentine with ramifying tubes prevails.
I have figured the right upper and lower mandibles of the type named
Edaphodon (_pavement-tooth_), in which there are _three_ teeth or
dental tubercles on each ramus of both jaws, _Lign. 191_: the lower
mandible is produced anteriorly into a falciform beak:[525] the
articulating surface of the symphysis (2 _s_) is broad at the base,
and contracts gradually forward until the margins meet at the apex. In
_Ischyodus_ the lower jaw is deeper, less produced in front, and the
margins of the symphysis are parallel until abruptly truncated at the
extremities: the upper jaw has _four_ tubercles on each side.
[525] Hence M. Agassiz proposed the name of _Psittacodon_
(parrot-tooth) for this genus of Chimæroids.
The upper jaw in Elasmodus has but three tubercles, as in Edaphodon,
but the dentine of which they are composed is confluent, being rolled
round like a scroll in the substance of the bone, one edge forming the
margin of the tooth, and the other being buried deep in its centre.
The dorsal fin-ray or spine of the Edaphodon is laterally compressed,
with the posterior margin grooved, and the edges armed with fine teeth:
I have a specimen of the spine, with a pair of inferior mandibles of
the same individual, imbedded in a block of chalk from Kent; by favour
of Mrs. Smith, of Tunbridge Wells.
[Illustration: Lign. 192. Fossil Teeth of Sharks.
Fig. 1.--Hybodus medius. _Lias._ _Lyme Regis._
2.--Hybodus raricostatus. _Lias._ _Bristol._
3.--Carcharodon productus. _Tert._ _Malta._
4.--Hemipristis serra (fragment). _Chalk._ _Ratisbon._
5.--Otodus Obliquus. _Tert._ _Sheppey._
]
Hybodus. _Lign. 192, figs. 1, 2._ (_Bd._ pl. xxvii^_d_.)--Intermediate
between the obtuse crushing teeth of the Sharks previously described,
and those sharp, angular, pointed, dental organs of the Squaloids,
are those of the fishes which M. Agassiz has arranged in a sub-family
or group termed _Hybodonts_; the teeth of which are characterised
by their transversely elongated form, and the series of subacute,
compressed, conical cusps or points, which compose the crown. The
median cone is the principal, the lateral points being shorter and
smaller, as in _Lign. 192, fig. 2_; in some species the difference
between the median and lateral cones is greater, in others less, as
in _fig. 1_. These cusps have a coating of dense enamel, which is
plicated longitudinally on both faces. The base, which almost equals
the crown in size, is composed of a coarse osseous substance. The
internal structure of the crown differs from that of the Cestracionts,
in having no principal pulp-cavity, and in being chiefly composed of
dendritical dentine, with reticulated medullary canals. The form and
organization of these teeth show them to have been instruments for
cutting and tearing food. The Hybodonts, as we have already stated (p.
581), possessed two spinous dorsal fins; in their habits and economy
they probably did not differ from the ordinary Sharks. Teeth and spines
of this genus are common in the Trias, Lias, Oolite, and Walden, and
occur in the Green Sand and Chalk. There are several species of teeth
and fins in the strata of Tilgate Forest (_Foss. Til. For._ pl. x.).
In general the teeth are found detached, but occasionally they occur
in their natural position, adhering to the mineralized cartilaginous
jaws (_Petrif. Lign. 97_); as in the beautiful fossil figured _Bd._
pl. xxvii.^_d_; and in the fine specimen of _H. basanus_, from the Isle
of Wight, figured in the _Geol. Soc. Journ._ vol. pl. iv. There are
several related genera, founded on the situation, form, and division of
the principal cusps of the teeth.
Sharks with Cutting Teeth.--The jaws of the common squaloid fishes, as
the Lamna (_Porbeagle_) and Carcharias (_Great White Shark_), are so
common in collections of natural history, as to render a description
unnecessary. The numerous vertical rows of angular, laterally
compressed, pointed teeth, with sharp or serrated edges--in some
species consisting of a simple trenchant cusp, in others with small
lateral teeth, or denticles, at the base, are characters with which all
are familiar. Fossil teeth of this form are extremely abundant in the
Tertiary and Cretaceous deposits; and are commonly in a beautiful state
of preservation. The genera of these fossil teeth are founded on the
solidity or hollow structure of the cusps, their possessing cutting or
serrated edges, and the presence or absence of lateral denticles. But
the last character cannot in every instance be relied upon, for some
recent Sharks have rows of teeth both with and without denticles.
Carcharodon productus. _Lign. 192, fig 3._--The genus Carcharias
comprises the large Sharks with cutting triangular teeth, crenated
(_notched_) on their margins, and having a broad base. In
_Carcharodon_, the teeth differ from those of Carcharias in being solid
in the centre, while in the latter they are hollow; but in both genera
the teeth exhibit the same reticulated structure of medullary and
calcigerous tubes. The _White Shark_ and other large species belong to
these genera; some of which are upwards of forty feet in length. But
even these colossal fishes must have been far surpassed in magnitude
by the extinct species of the Tertiary deposits, if the teeth afford
a scale of proportions; for some of the fossil teeth from Malta and
the United States are six inches long, and five wide at the base;[526]
being twice the size of the teeth in the largest living species. The
specimen figured in illustration, _Lign. 192, fig. 3_, is of a small
size.
[526] For instance, some of the Maryland specimens of _Carcharodon
megalodon_. See an admirable memoir on the Fossil Squalidæ of the
United States, by Dr. R. W. Gibbes, Journ. Acad. Nat. Science,
Philadelphia. At the meeting of the British Association in 1851, J.
S. Bowerbank, Esq. F.R.S. read some interesting observations on the
comparison of these large fossil fishes with the recent _Carcharias
glaucus_ of Australia. See also Owen, Cyclop. Anat. _Art._ Teeth.
Hemipristis serra. _Lign. 192, fig 4._--The fossil teeth of this genus
are distinguished by serrated edges, that do not extend to the summit,
which is a sharp angular point; as in the fossil represented.
[Illustration: Lign. 193. Fossil Teeth of Sharks. _Chalk._ _Lewes._
Fig. 1.--Corax pristodontus.
2.--Lamna crassidens.
3.--Notidanus microdon.
4.--Ptychodus polygurus; seen laterally.
5.--Ptychodus polygurus; viewed from above.
6.--Lamna elegans.
]
Lamna elegans. _Lign. 193, fig. 6._--The fishes of the genus _Lamna_
(to which the recent shark called the _Porbeagle_ belongs) have teeth
with smooth trenchant edges, and a small sharp denticle (_little
tooth_) on each side the base, as in the fossil, _Lign. 193, fig. 6_.
The specimen, _fig. 2_, although devoid of denticles, probably belongs
to the same genus, for reasons already explained. Several species
abound in the Chalk; and they are associated with teeth, which are
relatively wider and shorter, and have large compressed denticles; the
latter are arranged in a separate genus, named Otodus (_eared-tooth_),
by M. Agassiz. The specimen figured _Lign. 192, fig. 5_, represents
_O. obliquus_; another species, _Otodus appendiculatus_, is abundant
in the Sussex Chalk. The large, wide, triangular, smooth teeth, with
trenchant edges, and destitute of lateral denticles, so common in the
Chalk, are related to Lamna, and are comprised in the genus _Oxyrhina_
(_Poiss. Foss._ tom. v. tab. xxxiii.).
Notidanus microdon. _Lign. 193, fig. 3._--These teeth differ
remarkably from those of the other genera of Sharks. The crown of each
tooth is composed of a series of sharp angular enamelled points, the
first of which is the largest, and is notched on its anterior edge; the
base or root is osseous, flat, with a slight longitudinal depression
below the border of enamel. These teeth are comparatively rare in the
Chalk. One species has been found in the Oxford Clay; and several in
the Tertiary strata. Specimens occur in Hordwell Cliff.
Corax pristodontus. _Lign. 193, fig. 1._--The teeth of the fossil
_Corax_ chiefly differ from those of the recent genus _Galeus_, to
which the _Tope_, or Grey Shark, belongs, in being solid; they are of
a triangular form, with a deep concavity or notch on the posterior
margin, the base of which is prolonged and forms three or four angular
points: the anterior edge of the tooth is finely serrated. The root of
the tooth, as in _Notidanus_, is a broad osseous plate. There is much
diversity of form in the Chalk specimens, which are all of a small
size, as in _Lign. 193, fig. 1_. In Sussex they are more common in
the Chalk-marl than in the Chalk.
The only fossil teeth of the Shark family resembling those of the
tertiary Carchariodonts, that have been discovered in the strata below
the Chalk, are from the carboniferous deposits of Yorkshire and Armagh.
These teeth are compressed, triangular, crenated on the edges, with
large plaits or folds on the enamelled surface, towards the base of the
crown. M. Agassiz refers them to a new genus, viz. Carcharopsis, with
the specific name of _Prototypus_.
Fossil Vertebræ of Sharks.--As the cartilaginous nature of the
skeleton in this family renders it unfavourable to preservation in the
mineral kingdom, the durable parts already described, and those which
are ossified, are almost the only relics found in a fossil state.
The dermal integument is, however, sometimes preserved; and I had a
beautiful example of shagreen, composed of irregular minute hexagonal
scales, one of which is represented highly magnified, _Lign. 185,
fig. 1_.
In the _Galeus_ and _Carcharias_ the vertebræ are more ossified than
in many other genera of cartilaginous fishes, and fossil vertebræ of
these sharks often occur in the cretaceous and other strata. Groups of
vertebræ of a large size occasionally occur in the Sussex Chalk; they
are circular, biconcave, and very short; one specimen is four inches
in diameter, and one inch long; their concavities are consequently
shallow. These vertebra: are composed of two shallow conical disks,
which are united by their summits, at the axis, and are connected and
supported by numerous wedge-shaped plates, that radiate from the centre
to the periphery (see _Foss. South D._ pl. xxxiii. _fig._ 10). My
collection contained a connected series of forty small vertebræ from
the Chalk near Lewes, which probably belonged to the same species of
Shark as the dorsal spine named _Spinax major_ (_Poiss. Foss._ tom.
iii. pl. xl^_a_ _fig._ 6).
Squaloraia. In the Lias of Lyme Regis, that inexhaustible storehouse
of fossil treasures, a considerable portion of the skeleton of a very
remarkable fish, partaking of the characters of the Sharks and Rays,
was discovered by Miss Mary Aiming, and is now in the Museum of the
Bristol Institution.[527] In this fish the jaws are prolonged into a
beak, like the Pristis (_Saw-fish_). It has the head of a Shark, with
a long beak; vertebræ of the Rays; with pectoral and ventral fins,
almost equally developed; a tail armed with, a spine; and spinous
bosses, as in the true Rays.
[527] It is figured and described by Dr. Riley, Geol. Trans. 2d ser.
vol. v. pl. iv. See also Poiss. Foss. tom. iii. pl. xlii.
Fossil Pristis, or Saw-fish.--This well-known predatory fish, which is
allied to the Rays and Sharks, and referred by M. Agassiz to the family
of _Raiidæ_, has projecting from its snout an osseous, flat, horizontal
plate, or beak, equal in length to one-third of the fish, and armed on
each side by a row of elongated, compressed, pointed teeth, implanted
in sockets; the front margin of these teeth is convex, the posterior
concave; this defence is termed the saw, and constitutes a most
powerful weapon. The _Pristis_ has also numerous small obtuse teeth on
the jaws. The remains of the beak, or saw, of an extinct species of
Pristis have been discovered in the Bagshot Sand at Goldsworth Hill,
Surrey,[528] and three other species have been found in the London
clay of the Isle of Sheppey, and the Eocene beds at Bracklesham and
Hordwell.[529]
[528] Proc. Geol. Soc. vol. ii. p. 687.
[529] Two teeth are figured in Dixon’s Fossils of Sussex, pl. xii.; the
specimens are in the British Museum; see _Petrifactions_, p. 414.
Fossil Rays.--The teeth of these fishes are characterised by the
extraordinary transversal development of the median teeth in both
jaws. Instead of pointed teeth, they have wide, flat, tesselated
dentary plates in each jaw, composed of distinct pieces, juxtaposed and
connected by their margins, and united by fine sutures. In some species
the teeth are equal, in others of various sizes; they present numerous
modifications of arrangement, and are always disposed in symmetrical
rows. In the genus Myliobatis (_Eagle-ray_) the teeth of the median row
are of an extraordinary width, while their length does not exceed that
of the lateral plates, or chevrons, which are of an irregular hexagonal
form, and disposed in two or three rows on each side. There are five
living species of _Myliobatis_, and eighteen fossil species have been
found in the Tertiary strata at the Isle of Sheppey, Hordwell Cliff,
and Bracklesham Bay. I have figured a specimen of part of the upper
jaw of a species (_M. micropleurus_, _Lign. 194, fig. 2_), in which
the median teeth are very wide, and have two lateral rows of small,
irregularly hexagonal, plates. The surface of the teeth in this species
is smooth; but in others it is striated longitudinally (_Bd._ pl.
xxvi^_d_. _fig._ 14). In an allied genus, Ætobatis, from the Tertiary
beds at Bracklesham, the lower jaw projects beyond the upper, and in
each there is a row of flat, transverse teeth, _without_ lateral plates.
[Illustration: Lign. 194. Fossil Teeth of Fishes
Fig. 1.--Ceratodus emarginatus: 1/2 _nat._ _Lias Bone-bed._ _Aust Cliff._
A single dental plate.
2.--Myliobatis micropleurus: 1/3 _nat._ _Tert._ _Isle of Sheppey._
A series of six median teeth, with the corresponding lateral
teeth.
3.--Pycnodus Mantelli. _Weald._ _Tilgate Forest._ This specimen
consists of the _vomerine_ bone, with a median row of flat,
arched teeth, and two rows on each side of elliptical teeth,
arranged alternately.
]
To this notice of the fossil Rays, we may add, that a gigantic Torpedo
has been discovered in that celebrated locality of Ichthyolites, Monte
Bolca: and that Sir Philip Egerton has recently enriched his matchless
collection of fossil fishes, by a perfect Ray, from Mount Lebanon. It
is figured and described in the _Quarterly Geol. Journ._ vol. i. pl.
v. p. 225, under the name of Cyclobatis oligodactylus. It is a small
species, resembling the common Rays in its general appearance, but is
surrounded by a broad, flexible, cartilagino-membranous fin; the skin
is smooth, the teeth and eyes are small, the tail is slender; there are
no traces of dermal spines, tubercles, or defensive weapons. In many
points of structure it resembles the Torpedo; and may possibly, like
that fish, have possessed an electric organ. It is 3-1/2 inches long,
and 3 inches wide across the expanded fins.
CHAPTER XV.
FOSSIL ICHTHYOLOGY; COMPRISING THE GANOID, CTENOID, AND CYCLOID FISHES.
The fishes we have hitherto examined belong to the first order, the
_Placoidians_; we now pass to the fossil remains of the second order,
the _Ganoidians_, which are distinguished by their brilliant angular
scales, formed of osseous or horny plates, densely covered with enamel.
This order contains six or more families, comprising many genera and
numerous species; our investigation must be restricted to a selection
from the principal genera of the _Ganoids_, properly so called, and of
the _Sauroids_, or lizard-like fishes.[530]
[530] The fishes of these orders are described in _Poiss. Foss._ tom.
ii.
The first family, termed Lepidoides, contains several genera, which
are defined as possessing either numerous rows of brush-teeth, or
of obtuse conical teeth; flat, rhomboidal scales, arranged parallel
with the body; and an osseous, or partially osseous, skeleton. In one
division of this family, the body is either elongated or fusiform, the
mouth furnished with brash-teeth only, and the tail heterocercal, or
unequally bilobed (see p. 576). To this group belong several genera,
which are restricted to the Secondary formations more ancient than
the Oolite; while the other group, with homocercal tails, lived in
the Oolitic and Cretaceous seas. Two genera, in particular, abound
in the Permian and Carboniferous strata; namely, _Amblypterus_ and
_Palæoniscus_.[531]
[531] For the characters, affinities, and distribution of these and the
allied genera of the Heterocerque Ganoid fishes, see Sir P. Egerton’s
Memoir in the sixth volume of the Quarterly Geological Journal.
Amblypterus. _Lign. 187._ _Wond._ p. 740. _Bd._ pl. xxvii.^_b_.--The
fishes of this genus, as the name indicates, have very large and wide
fins, composed of numerous rays. The scales are rhomboidal and finely
enamelled; the tail is heterocercal. The figures referred to convey a
correct idea of the form and external characters. Beautiful pyritous
imprints of Amblypteri occur in the Carboniferous slate of Saarbrück,
in Lorraine; and fine specimens in the ironstone nodules of the same
locality. On the shore at Newhaven, near Leith, similar fossils occur
in nodules washed out of the cliffs of coal-shale (_Bd._ p. 278).
Palæoniscus. _Ly._ p. 304.--The fishes of this genus differ from
those of Amblypterus in the relatively moderate size of the scales,
and the numerous little rays on their margins. They have rhomboidal
scales, which in some species are very small, and in others large.
They have numerous brush-teeth. Several peculiar species, found in the
marl-slates and magnesian limestones of the Permian system, are very
widely distributed, occurring in the British Isles, Germany, and the
United States.
In some localities the small species occur in groups; on a slab of
red sandstone, in the Museum of the Geological Society, from Tyrone,
between two and three hundred perfect fishes (_P. catopterus_) are
imbedded on a space not exceeding two feet square.
A remarkable circumstance relating to the fishes of this genus is the
almost constant absence of the bodies of the vertebræ in otherwise
well-preserved specimens, and in which the spinal processes and the
ribs are entire: occasionally, however, examples occur with some of the
vertebræ perfect. An explanation of the above phenomenon may perhaps
be found in the probable originally cartilaginous nature of the bodies
of the vertebræ, and the osseous structure of the enduring apophyses
and ribs;[532] while those rare specimens which possess a few bony
vertebræ may be regarded as exceptions, in which ossification took
place in a structure essentially cartilaginous.
[532] Professor Owen states that a similar condition of the spinal
column obtains in the fossil Microdonts.--_Rep. Brit. Assoc._ 1846.
The fishes found in the copper-schists of the Zechstein, at Mansfeld in
Saxony, are generally impregnated with copper pyrites, and their scales
are as brilliant as burnished gold. These ichthyolites are almost
always in contorted and twisted positions; which appearance M. Agassiz
attributes to contraction of the muscular tissues after death, during
the progress of decomposition, and before the fishes sank down and
became imbedded in the mud. (_Poiss. Foss._ tom. ii. p. 70.)
The fishes of the genus Palæoniscus are often found in the shales and
marls of the Permian and Carboniferous systems of England and Scotland.
At East Thickley, in the county of Durham, numerous specimens have
been found.[533] The lower Carboniferous strata at Burdie-house, a
locality we have before mentioned, have yielded several species of
Palæoniscus, associated with teeth and other remains of large sauroid
fishes.[534] On the continent also they prevail in deposits of the same
epoch; Eisleben and Mansfeld, iii Saxony, are well-known localities.
In North America they have been discovered in strata of probably the
same age.[535] In fine, the genera Amblypterus and Palæoniscus may
be regarded as characteristic "medals" of the geological epoch which
intervened between the Devonian and Triassic formations.
[533] See Professor Sedgwick on the Magnesian Limestone. Geol. Trans.
2d ser. vol. iii.; and Prof. King’s Monograph on the Permian Fossils,
published by the Palæontographical Society.
[534] Dr. Hibbert’s Memoir on the Fossils of Burdie-house.
[535] Geology of Massachusetts, by Professor E. Hitchcock.
We will next examine a few genera of the homocercal Lepidoids and
Pycnodonts, whose relics are chiefly distributed in the Lias, Oolite,
Purbeck, and Wealden.
[Illustration: Lign. 195. Outline of the Dapedius. _Lias._ (1/2 _nat.
size_).]
Dapedius. _Lign. 195._--At Lyme Regis, and other productive localities
of the fossils of the Lias, large masses of angular enamelled scales,
and occasionally entire specimens of the fishes to which they
belonged, have for many years been collected. Sir H. De la Beche first
scientifically investigated the structure of these Ichthyolites, and
pointed out their characters and relations. The Dapedius (of which
a restored figure is given in _Lign. 195_) is a flat, laterally
compressed fish, with a rounded head, and fins of moderate size. The
body rapidly contracts towards the root of the tail, the fin of which
is large and symmetrically lobed. The mouth is furnished with several
rows of small conical teeth, which are crenated at their summits,
and has brush-teeth on the palatine bones; the jaws are short. The
scales are rhomboidal, highly polished, and united laterally by short
processes; as in many other ganoid fishes. It belongs to the Lepidoids.
The Tetragonolepis is a Liassic fish, very similar in shape to the
Dapedius. It was formerly grouped with the _Lepidoidei_, but Sir P.
Egerton has lately discovered that it essentially differs from those
fishes in the character of its scales and teeth, and that it belongs to
the Pycnodonts.
Lepidotus.[536] _Lign. 186, 196, 197._--Scales of a dark-brown, almost
black colour, with a glossy enamelled surface, and of a rhomboidal
or lozenge form, and teeth equally dark and glossy, of an obtuse
hemispherical figure, are very common in the Wealden strata of the
south-east of England and in the Isle of Purbeck. They are called by
the quarry-men _fishes' scales_ and _eyes_. The collectors of the
last century used to term the obtuse circular teeth of this and the
related genera _Bufonites_, from a supposition that they were formed
in the heads of toads. These relics belong to an extinct genus named
_Lepidotus_, which contains numerous species, that are distributed in
the Oolite, Purbeck, and Wealden formations. These fishes resembled the
Carps in their general form, but they have no anatomical relations to
that family. The body is covered with large rhomboidal scales, which
are protected on the external surface by a thick plate of enamel (Lign
196, _fig._ 3). The lateral line, which is slightly arched, passes
direct from the operculum to the middle of the insertion of the caudal
fin. The head, and even the face, are cased with osseous and enamelled
plates. The bones of the surface of the skull are very large, and are
connected by sinuous sutures. The jaws are short and rounded, and
furnished with a row of obtuse, conical, circular teeth (see _Lign.
197_), and several rows of sessile teeth, more or less contracted at
the base, which forms a very short pedicle that is anchylosed to the
bone. The fossil Lepidoti are found, for the most part, in fluviatile
deposits, as in the Purbeck and Wealden strata; and it is probable they
inhabited the rivers or sea-coasts, and not deep waters.
[536] _Poiss. Foss._ tom. ii. p. 233.
[Illustration: Lign. 196. Scales and Fin of Lepidotus Mantelli.
_Wealden._
_Tilgate Forest._ (_Nat. size._)]
Fig. 1.--Scale, with a single process of attachment.
2.--One of the scales of the dorsal line.
3.--Scale (external surface), with a bifurcating process of
attachment; the enamelled portion (which alone is visible when
the scales are in their natural position on the animal) has
longitudinal grooves or folds.
4.--Scale (viewed on the inner surface), having a bifurcating
process of attachment and a tooth or projection on each side,
to connect the scale laterally with the adjoining scales.
5.--The front ray of the dorsal fin, covered with two rows of
enamelled scales, and another ray behind it.
The scales and teeth figured _Lign. 196, 197_, belong to the larger
species of the Wealden. The remains of this fish were first collected
in Tilgate Forest, and several teeth and: scales are figured _Foss.
Til. For._ pl. v. and x.; considerable portions of connected scales
have since been found; also the head entire, and the fins more or less
perfect. A specimen in my collection retained a mass of the scales near
the insertion of the tail, a foot wide; indicating the original to
have been twelve feet long, and its body three feet broad. The scales
are distinguished from other species by the folds or grooves on their
enamelled surface; and the teeth by the contracted base, or pedicle,
which is a little narrower than the crown (_Lign. 197_, and _Pl. VI.
fig. 10_). A species (_L. Fittoni_) closely related to the above is
equally abundant in the Weald of Sussex; the scales are not striated,
and the teeth have no pedicle.
[Illustration: Lign. 197. Portion of the Jaw of Lepidotus. _Wealden._
_Tilgate Forest._ (_Nat. size._)
This specimen shows three successional teeth beneath a row of teeth in
use.]
The intimate structure of the teeth of the Lepidotus is beautifully
preserved, and may be easily examined in thin transverse and vertical
sections, viewed by transmitted light: see _Pl. VI. fig. 10_. The
dentine is composed of bundles of tubes, continued from the cells of
the osseous base, radiating in a vertical direction to the surface of
the tooth, as seen in _Pl. VI. fig. 10_, and giving off branches at an
acute angle; but when more highly magnified, the finer branches are
seen to be spread out and arched at their extremities, "presenting the
appearance of the stems of corn, beaten down by heavy rain."[537]
[537] Odontography, p. 70. See the beautiful representation of this
structure, pl. xxxi.
The dorsal and pectoral fins of these fishes are very strong, and
consist of several bony rays. There is a double row of acuminated
enamelled scales, arranged more or less obliquely, on the anterior
margin of the dorsal and anal fins, and on both margins of the caudal:
part of the first ray of a dorsal fin, with scales, is represented
_Lign. 196, fig. 5_.
A small species of Lepidotus (_A. minor_) is common in the Purbeck
limestone, and specimens may often be procured from the quarries near
Swanage;[538] it has also been found at Hildesheim, in Saxony, by M.
Roemer. The detached scales abound in the limestones; and the splendid
fossil reptile from Swanage, figured _Petrif. Lign. 38_, is sprinkled
with the scales and minute teeth of this fish.
[538] Fine specimens of this fish are in the British Museum
(_Petrifactions_, p. 429), and in the Museum at Dorchester.
The majority of the species of Lepidotus belong to the Lower Oolites
and the Lias. The habits of the Lepidoti, as indicated by the form and
structure of the teeth, were those of fishes whose food consisted of
crustaceans, shelly mollusca, &c.; for the dental organs are peculiarly
adapted for the crushing and grinding of such substances; and the teeth
of the adult fishes are generally worn down by use.
Pycnodus. _Pl. I. fig. 3_; _Lign. 194, fig. 3._--The fishes of
the family of Pycnodonts, so named from the thickness of their teeth,
have an osseous skeleton, a flat body covered with rhomboidal scales,
and flat or rounded teeth disposed in several rows on the palatine,
vomerine, intermaxillary, and premandibular bones.[539] As in the
Lepidotus, these teeth are constructed for crushing, and have generally
a smooth, dense, convex or flattened crown, with a highly polished
surface. This genus belongs chiefly to the Oolite; it is found also
in the Lias, Chalk, and Wealden. A perfect fish of the genus Pycnodus
(_P. rhombus_), from the Jura limestone, at Torre d’Orlando, near
Castellamare, is figured in the frontispiece of the first volume of
this work; and a vomerine bone, with teeth, from Tilgate Forest, in
_Lign. 194, fig. 3_. In the last fossil there is a median row of
flat,, elongated, transversely arched, smooth, glossy teeth, with a
double alternate row of small sub-circular teeth on each side, attached
to the bone, which is imbedded in Tilgate grit. Specimens of this kind,
belonging to one or more species of Pycnodus, occur in the Wealden
of Sussex; they were among my earliest discoveries in Tilgate Forest
(_Foss. Til. For._ pl. xvii. figs. 26, 27). Examples are met; with in
which all the teeth are shed, and the bony plate of the vomer alone
remains.
[539] The intermaxillary, palatine, and vomerine bones compose the
vault or roof of the mouth; the vomer occupying the middle; the
intermaxillary the front; and the palatine bones the sides; the
premandibular bones belong to the lower border of the mouth.
Gyrodus. _Lign. 198._--In another genus of the Pycnodonts, termed
Gyrodus, the crowns of the teeth are deeply furrowed, the structure
of the dentine is very dense, and the pulp-cavity large and simple.
One species occurs in the Speeton clay of Yorkshire, and another in
the Sussex weald; but the teeth are chiefly found in the Oolite and
Chalk. As in Pycnodus, the teeth are distributed in rows on the bones
composing the roof, floor, and sides of the mouth.[540]
[540] An extraordinarily perfect lower jaw of a Gyrodus is to be seen
in the British Museum (_Foss. Brit. Mus._ p. 439).
These characters are beautifully displayed in the Russian specimen,
_Lign. 198_. This interesting fossil was presented to me by the late
Stephen Cattley, jun. Esq., who collected it in 1839, in a valley near
Rjeff, a village on the banks of the Volga. Mr. Cattley informed me
"that many fossils are found in that and the neighbouring valleys;
and the locality is frequented by Russian geologists when the season
permits, which is but seldom, owing to the long duration of the snow,
and the heavy rains which accompany the thaw." This specimen consists
of the vomerine bone, which is of a coarse texture, and five rows of
teeth; the median row consists of very large elliptical teeth; those
of the lateral rows are much smaller and arranged alternately. The
peculiar structure of the teeth of this genus[541] is finely displayed
in this fossil. The ample, deep, and simple pulp-cavity is seen in
several teeth, where the crown of dentine has been worn off, filled
with a pure white calcareous spar; one of these cavities is marked a.
The dentine is extremely dense, consisting of very minute calcigerous
tubes, and passes into an external layer of enamel.
[541] Odontography, p. 72.
[Illustration: Lign. 198. Gyrodus Murchisoni[542] (G. A. M.) _Oolite?_
_Russia._
(_Collected by the late Stephen Cattley, jun. Esq._)]
Fig. 1.--The vomerine bone of a fish, with five rows of teeth; seen
from above; many of the crowns of the teeth are worn away
by use, and the large pulp-cavities, filled with white spar,
are exposed; as at _a_.
2.--Lateral view of the same.
_a._ One of the pulp-cavities filled with spar.
[542] It is with peculiar pleasure that I inscribe this new species of
_Gyrodus_ to Sir R. I. Murchison, in commemoration of those extended
and successful geological researches in the Russian empire, which have
conferred additional honour on his distinguished name.
The fishes of the genus _Gyrodus_ have the body large, flat, and
elevated; the dorsal and anal fins are very long; and the tail is
forked, with equal elongated lobes. The scales are laterally connected
by strong processes, as in Lepidotus.
Other genera related to the foregoing occur in the Oolite; as for
example, Microdon, thus named from the smallness of its very numerous
flat angular teeth, arranged in many rows; Placodus, in which the teeth
are few, flat, and of great size;[543] and Platysomus (_flat-body_),
with orbicular, clavate, teeth.
[543] Odontography, pl. xliii. _fig._ 1, and pl. xxx. _fig._ 2.
In these fishes, also, the dental organs are well adapted for the
comminution of shell-fish, and other hard bodies.
Cephalaspides of the Devonian System.--The remains of the three genera
of Ganoid fishes that we have now to notice are of a very remarkable
character, and are found exclusively in the Devonian or Old Red system;
most frequently in Scotland, but also in other parts of the British
Isles, and in Europe and America. These fishes agree in one general
character, that of having extensive osseous plates, or scutcheons;
their general aspect will be understood by reference to _Lign. 199,
200, 201_. There are no vestiges of the bodies of the vertebræ, which,
therefore, were probably cartilaginous. These fishes constitute a
distinct family with the name _Cephalaspides_, from the character of
the first genus we propose to describe.
[Illustration: Lign. 199. Cephalaspis Lyellii. (1/4 _nat. size_.)
_Devonian._ _Forfarshire._
Crushed specimen; seen from above.]
[Illustration: Lign. 200. Cephalaspis Lyellii. (1/4 _nat. size_.)
_Devonian._ _Glammis, Forfarshire._
Lateral view, showing the produced dorsal lobe of the tail.]
Cephalaspis Lyellii. _Lign. 199, 200._--The most striking feature in
the Ichthyolites of this genus is the enormous scutcheon, or buckler,
which forms the head, and is prolonged posteriorly into two lateral
horns or points; this part so closely resembles the cephalic shield of
certain trilobites (see _Lign. 175_), that the first found specimens
were supposed to be the remains of unknown crustaceans. The name
_Cephalaspis_ (_buckler-head_) is derived from this character. This
remarkable appearance is occasioned by the intimate anchylosis of
all the bones of the cranium. The body of these fishes is relatively
smaller than the head; it has one dorsal fin, and terminates in a
tapering tail, supporting a fin. There are two small eyes, placed
towards the middle of the head. The body is covered with rhomboidal
scales; and the head with discoidal scales, which are highly ornamented
with radiated markings[544] (_Ly._ p. 344, _fig._ 396). There are four
species of Cephalaspis at present known.
[544] Poiss. Foss. tom. ii. p. 135.
The other genera are equally unlike any recent types of the class of
fishes. No perfect examples have been found, and some parts of their
structure are still unknown; the annexed figures, _Lign. 201_, have
been drawn by Mr. Dinkel (the eminent artist employed by M. Agassiz),
with scrupulous accuracy, no part being introduced which is not clearly
demonstrated in some one specimen; and the form of the scutcheons is
made out very distinctly, to aid the collector in discriminating the
detached plates, which are the most common relics of these singular
beings.
Pterichthys cornutus.[545] _Lign. 201, fig.1._--This fish is
distinguished by its two wing-like lateral appendages; whence the name
of the genus (_winged-fish_). These processes, like the spines on the
gill-covers of the common Bullhead (_Cottus gobio_), are weapons of
defence. In some specimens they are extended at right angles to the
body (_Ly._ p. 345, _fig._ 400).
[545] The first fish of this genus was discovered by Mr. Hugh Miller,
in whose charming little work, "The Old Red Sandstone; or, New Walks
in an Old Field," will be found a very graphic description of the Old
Red fishes; I know not a more fascinating volume on any branch of
British geology. Consult also Sir P. Egerton’s elaborate paper on the
_Pterichthys_ in the Geol. Journal, vol. iv. p. 302.
The head and anterior part of the body are covered with large angular
tuberculated scutcheons. The under surface of the body is flat and
protected by five plates, a quadrangular plate occupying the centre.
The upper part of the body is convex; the form and disposition of the
dorsal scutcheons are shown in _Lign. 201, fig.1_. There are two
eyes, which are placed in front of the lateral spines: see _fig. 1._
The tail is of an angular form, and as long as the body; it is
covered with scales, and considered by M. Agassiz to have been the only
instrument of locomotion. The British species of this genus, of which
ten are known, are all very small, varying in length from one to ten
inches.
[Illustration: Lign. 201. Fossil Fishes of the Devonian System.
(_Drawn by Mr. Joseph Dinkel._)
Fig. 1.--Pterichthys cornutus, seen from above.
2.--Coccosteus oblongus.
These figures are restored with great care, from the best preserved
specimens hitherto discovered.]
Coccosteus oblongus. _Lign. 201, fig. 2._--The fishes of this
genus, as may be seen by the lignograph, very much resemble those
of Pterichthys; in both the osseous scutcheons of the body are very
similarly disposed. In _Coccosteus_, the head[546] is somewhat rounded;
slight rounded notches on the edge of the buckler indicate the place of
the eyes on the sides of the head. There is no indication of lateral
spines. The tail is very long, covered with scales, and supports a fin.
The plates of the body are tuberculated, as in Pterichthys. There are
six or eight teeth on each half of the lower jaw (and probably as many
on the upper), with a curious group of teeth situated on its symphisis.
The teeth are chiefly composed of bone, passing into dentine at their
surface.[547]
[546] This is of course only the cranial buckler of the animal, for,
as Mr. Hugh Miller observes, "of the true internal skull there
remains not a vestige. Like that of the Sturgeon, it must have been a
perishable cartilaginous box."--_Miller’s Foot-prints_, p. 50.
[547] Miller, Rep. Brit. Assoc. 1850. Transact. Sect. p. 92. In the
Annals of Natural History for November, 1848, Professor M‘Coy has given
a corrected outline of the carapace, or bony cephalo-thoracic casing,
of the Coccosteus. See also Miller’s Foot-prints, _fig._ 11.
These fishes are from a few inches to two feet in length; six species
have been discovered; and their remains are the most abundant of the
Ichthyolites of the Old Red. Patches of detached scales, and isolated
osseous plates, are very frequent in the sandy cornstones, and the
subcrystalline masses of limestone. These fragments are usually of a
brilliant blue or purple colour; and, strongly contrasting with the
dull red tint of the surrounding rock, are easily recognised. The
colour is supposed to be due to the presence of phosphate of iron,
which has communicated a similar tint to the Ichthyolites of the
Caithness Schist.[548]
[548] Murch. Sil. Syst. p. 588; see also a detailed description of
the Cephalaspis, Holoptychius, and other Devonian Ichthyolites, by M.
Agassiz, ibid. p. 589-601.
Fossil Sauroid Fishes. (_Poiss. Foss._ tom. ii.)--The family of Ganoid,
fishes termed _Sauroid_, or lizard-like, by M. Agassiz, are so named
in consequence of certain peculiarities in their organization which
are found in no other animals of this class, but exist in reptiles.
There are but two living genera; namely, the _Lepidosteus_, of which
there are many species that inhabit the rivers of America; and the
_Polypterus_, that contains two species, one inhabiting the Nile, and
the other the rivers of Senegal. In these fishes the bones of the
skull are closely connected by sutures; the teeth are large, conical,
and longitudinally striated, as in the crocodile, plesiosaurus, &c.;
the spinous processes are united to the bodies of the vertebræ by
suture, as in most reptiles; and the ribs are articulated to the
extremities of the transverse processes; the skeleton is osseous. Even
in the soft parts many analogies to reptilian structure are seen;
thus the Lepidosteus has a glottis, as in the _Siren_; and a cellular
air-bladder, with a tracheal vessel, resembling the lungs of an
Ophidian (_serpent_). These fishes are the only living representatives
of those voracious tribes of the most ancient marine fauna, whose
remains abound in the Secondary formations. Their relics have often
been mistaken for those of reptiles; particularly the teeth, which
from their large size, conical figure, enamelled and striated surface,
and internal cavity, were generally supposed to belong to crocodiles.
The scales are flat, rhomboidal, and parallel to the body. The recent
_Lepidosteus osseus_, of North America, affords a good illustration
of the fossil genera; a reduced figure of this fish, from _Poiss.
Foss._, will be found in _Bd._ pl. xxvii^_a_.; and teeth of some fossil
Sauroids are represented _Bd._ pl. xxvii.
The teeth of the Sauroids consist of two kinds; namely, large pointed
striated cones, and numerous small brush-teeth. The intricate structure
of the conical teeth of the _Stony-gar_, or Lepidosteus, is very
remarkable, and presents some analogy to that observable in the dental
organs of the Labyrinthodon, an extinct genus of reptiles, of which
we shall treat in a subsequent chapter. The tooth consists of a large
conical pulp-cavity, surrounded by a mass of dentine, which is plicated
longitudinally, its folds giving to the pulp-cavity an appearance of
being divided into parallel longitudinal branches; resembling, in
this respect, the base of the tooth of Ichthyosaurus, as shown in a
transverse section, _Pl. VI. fig 9_. If we imagine these folds to be
multiplied, and to have more inflections, and the pulp-cavity to be
reduced in its proportions, we shall have the elegant organization
of the teeth of the _Labyrinthodonts_ (see _Pl. VI. fig. 3^b_). The
dentine is composed of very minute calcigerous tubes, which pass off at
right angles from the pulp-cavity to the periphery; and it is covered
by a layer of cement, or coarser dentine, which is encased in a coat
of enamel, forming the external investment of the tooth.[549] The long
conical teeth are implanted in _alveoli_ or sockets, to the walls of
which they are anchylosed at their base.
[549] These remarks are based on M. Agassiz’s description and my own
observations. An interesting paper, "On the Microscopic Structure of
the Teeth of the _Lepidostei_, and their analogy with those of the
_Labyrinthodonts_, with a plate," by _Dr. Jeffries Wyman_, will be
found in Amer. Journ. of Science, October, 1843, p. 359.
Lepidostei.--This family, having the above described recent
_Lepidosteus_ for its type, comprises several genera, and is
represented in all the formations from the Tertiary to the
Coal-measures inclusive. The _Lepidosteus_ itself has left its remains
in the Eocene tertiary of England. The Lepidotus (before described,
p. 604,) ranges from the Chalk to the Lias; the _Pholidophorus_ and
_Dapedius_ (p. 603) abound in the Lias; the latter being found also
in the Wealden, and the former in the Oolite and Purbeck; and the
_Palæoniscus_ (see p. 601) is a well-known Permian and Carboniferous
form.
Sauroidei.--The remains of the Sauroids proper occur in the Chalk,
Purbeck, Oolite, Lias, Permian, and Carboniferous rocks. The great
strength and size of some of these teeth prove that the seas of
those remote periods were inhabited by voracious fishes of enormous
magnitude. See _Petrif._ pp. 432, _et seq._
The teeth and jaw of a gigantic sauroid (_Megalichthys_), from the
Carboniferous strata at Burdie-house, are figured _Bd._ pl. xxvii.; the
sections of the teeth shown in figs. 13, 14, of that plate, illustrate
the size of the pulp-cavity and the thickness of the layer of dentine.
These remains were associated with the plants and crustaceans
previously described; an assemblage of fossils indicating a lacustrine
or estuary formation. Similar teeth have been found in the cannel-coal
of Fifeshire.
In the Upper Lias of Ilminster, Somerset, the nodular calcareous rock
is rich with the remains of the _Pachycormus_, many fine specimens of
which Mr. C. Moore, of that town, has successfully worked out from
their stony encasement, exhibiting the gaping, contorted fish, as it
died in the convulsive throes of suffocation in the muddy sea. The
little sauroid _Leptolepis_, of the Lias and the Purbeck, is also
abundant in the above mentioned locality.
In the lithographic stone of Solenhofen, and in the Purbeck strata,
Oxford Clay, and Lias of England, occur specimens of a sauroid fish
remarkable for the extreme shortness of the lower jaw, and the
prolongation of the upper into a beak; it is named _Aspidorhynchus_ by
Agassiz. The figure of this fossil fish is contrasted on pl. xxvii^_a_.
_Bd._ with that of its recent ally, the _Lepidosteus_.
In the Shanklin sand and in the Galt of Kent and Sussex, large,
conical, striated teeth belonging to sauroid fishes are occasionally
found. They invariably occur detached, and no portion of the jaws has
been observed. In the Chalk of Sussex several fine sauroid fishes have
been discovered; such as the _Lophiostomus_,[550] _Belonostomus_,[551]
and _Caturus_; the last two of which are found in the Oolite and Lias
also. These have been described and figured in the late Mr. Dixon’s
"Geology and Fossils of Sussex."
[550] _Geol. Surv._ Dec. 6. pl. x. xi.
[551] _Petrif._ p. 431.
The Sauroidei-dipterini[552] are found almost exclusively in the
Devonian formation. _Osteolepis_, _Diplopterus_, and _Dipterus_ are
characteristic members of this family. Interesting descriptions and
instructive figures of the structure of these genera are given in
Mr. Hugh Miller’s late work, "Foot-prints of the Creator, or the
Asterolepis of Stromness," at pp. 50 to 61.
[552] The characters of the scales of this and the next family, as well
as of the Acanthodei, are succinctly given in Miller’s Foot-prints of
the Creator, pp. 30, _et seq._
Cœlacanthi.--This is a numerous family of sauroid fishes, that have
derived their name, _hollow-spine_, from the central cavity in the
fin-rays, which, however, may have had originally cartilaginous
cores. They are found from the Devonian to the Cretaceous series. In
the former, one of the most remarkable is the genus _Holoptychius_,
distinguished by the peculiar structure of the scales; the enamelled
surface of which is covered by undulated furrows. The whole body is
covered by thick enamelled scales of this kind. A splendid specimen,
twenty-eight inches long, and twelve wide, is figured _Murch. Sil.
Syst._ pl. ii.^{_bis._} Scales have been found exceeding three inches
in length, by two and a half in width; which must have belonged to a
fish of great magnitude. _Ly._ fig. 395.
In the Old Red Sandstone of Elgin, at a quarry at Scat-craig, some
peculiar teeth occur, which possess a very remarkable structure, and
have been referred to a genus of sauroid fishes, which, from the
dendritical or arborescent disposition of the calcigerous tubes,
Prof. Owen has named _Dendrodus_. These teeth are of a conical form,
slightly curved, and solid throughout. On the external surface they
are finely striated longitudinally, and have two opposite vertical
ridges; the base is rough, and its margin rounded, as if for attachment
to a shallow socket. The largest specimen is one and a half inch in
length. In thin sections, viewed microscopically by transmitted light,
there is a central pulp-cavity, of small size; the medullary canals
pass into a few short ramifications, like the branches of a shrub, and
these are distributed into irregular dilatations, simulating leaves,
which resolve themselves into radiating bundles of calcigerous tubes; a
portion of a transverse section[553] is shown _Pl. VI. fig. 8_.
[553] Odontography, pl. lxii. B _fig._ 2; and Cycl. Anat. _Art._ Teeth.
[Illustration: Lign. 202. Asterolepis. _Devonian._ (1/2 _nat. size_)
Inner side of portion of the lower jaw.
(After Miller.)]
[Sidenote: ASTEROLEPIS.]
In Mr. H. Miller’s charming work just referred to we have a full
and clear account of the singular fossil fish the Asterolepis.
Remains of this gigantic Ganoid were first found in Russia.[554]
Its name is derived from the stellate markings on the dermal plates
of the head, which are of great size, and form a strong expanded
buckler, the orbits of the eyes being situated near the anterior
border. (See Miller’s _Asterolepis_, pp. 74, _et seq._ figs. 27-29.)
_Lign. 202_ shows a part of the lower jaw of this fish, seen on the
inside. Along the upper margin are seen a "thickly set row of small
broadly-based teeth,"--these are ordinary _fish_-teeth; and behind this
edge-row of small teeth, _b_, there occur "a thinly set row of huge
_reptile_-teeth, based on an interior platform of bone, which formed
the top of the cartilage enclosing box composing the jaw." (Miller.)
These large teeth, _a a_, are longitudinally striated, and generally
bear two sharp lateral cutting edges.[555]
[554] Casts of the fossil bones from Russia are in the British Museum;
_Petrif._ p. 435.
[555] The microscopic structure of both kinds of teeth is elegantly
figured in Mr. Miller’s work, pp. 81, 82.
Macropoma Mantelli. _Wond._ p. 348. (_Foss. South D._ tab. xxxvii.
xxxviii.; _Petrif._ p. 436, _Lign._ 89.)--This Cœlacanth fish is
from one to two feet in length, of an elongated fusiform shape, with
a large head and two dorsal fins; the anterior fin is imbedded, and
has seven or eight strong spinous rays, the first two of which have
numerous spines. The opercula are very long and large (hence its
name); the scales[556] are garnished with adpressed spines, disposed
in semicircular rows (see _Lign. 185, fig. 2_). The teeth are small,
conical, and numerous.
[556] See Prof. Williamson’s Memoir, Philos. Trans. 1849, p. 435; pl.
xliii. figs. 27, 28.
Several specimens of this fish are almost perfect. The bones of the
cranium, the jaws, teeth, opercula, branchial rays, palatine arches,
the surface of the body covered with scales, all the fins, the pelvic
bones, the vertebræ and their apophyses, all remain.
In one example, the vomer, covered with minute teeth, is exposed.
But the most extraordinary fact relating to these Ichthyolites, is
the preservation, in every specimen, of the air-bladder;[557] even
its membranes remain, and separate in flakes; and the ramification
of the minute vessels is visible under a high magnifying power. In
some instances this bladder is displaced and much distended; but in
general it occupies its natural position, and retains its elongated,
sub-cylindrical form, with a few annular constrictions or folds.
[557] See Williamson, _op. cit._ pp. 462-165, and figs. 29, 30.
[Sidenote: COPROLITES. COLOLITES.]
Coprolites. _Lign. 139, figs. 1, 2._--In more than one example
the solid earthy residue of digestion, in small lumps or pellets,
of a conical form and spirally convoluted, lies in the abdomen of
these fossil fishes. Fossil excrementitious substances of this kind
are termed _Coprolites_ (_Bd._ p. 198, pl. xv.); they occur in many
deposits, and belong not only to fishes, but to large reptiles and
other animals. _Lign. 139_, p. 432, _fig. 1_, represents the coprolite
of a _Macropoma_; and _fig. 2_, that of a species of _Shark_, from
Hamsey. The convoluted appearance of these bodies arises from the
peculiar organization of the intestinal canal of the original fishes,
in which, as in the recent Dog-fish, a portion of the intestine was
spirally twisted, the tube forming several gyrations; and the passage
of the calcareous substance through this constricted canal gave rise
to the structure observable in the coprolites. In the Macropoma the
gyrations appear to have been few; seldom more than five or six
turns being apparent. In the fossil Sharks the convolutions are more
numerous, ten or twelve occurring in the length of an inch. In many
of the coprolites, the impression of the mucous or lining membrane of
the intestinal canal may be detected. Some of the coprolites of the
Macropoma are not convoluted; probably from having occupied the upper
part of the digestive tube, and therefore not having been moulded in
the spiral part. (See _Geol. S. E._ p. 145. _Foss. South D._ tab. ix.)
Minute scales and bones of fishes are occasionally imbedded in the
substance of the coprolites, affording evidence of the carnivorous
habits of the Macropoma.
Cololites. _Bd._ pl. xv^_a_--It will be convenient to notice in this
place those curious fossils which occur in detached masses in the
limestone of Solenhofen, and used to be known to collectors by the
term _lumbricaria_, from the supposition that they were petrified
earth-worms. An excellent representation of a fine specimen is given
by Dr. Buckland in the plate referred to above. These convoluted
bodies M. Agassiz, with his wonted sagacity, has ascertained to be
the intestines of fishes; and has therefore named them _Cololites_.
Although generally found isolated, specimens occur in which they are
imbedded, like the coprolites of the Macropoma, in the abdominal
region of fishes. The frequent occurrence of the _Cololites_ apart
from the body, is explained by the usual process of decomposition in
fishes. M. Agassiz remarks that dead fish always float on the surface
of the water with the belly uppermost, until the abdomen bursts from
distention. The small intestines are then expelled by the evolved gases
through the aperture, and soon become detached from the body. I have
observed indistinct traces of similar remains in the beds of chalk in
which fossil fishes most prevail. Dr. Buckland mentions the discovery,
by Lord Greenock, of a mass of petrified intestines distended with
coprolite, and surrounded by the scales of a fish, in a block of
coal-shale from the neighbourhood of Edinburgh (_Bd._ p. 199).
Dercetis elongatus. _Wond._ p. 349.--Before proceeding to the
investigation of examples of the next order, I will describe a highly
interesting Ichthyolite, which in a mutilated state is extremely
common in some of the chalk strata of the South-east of England; it is
noticed in _Foss. South D._ p. 232. This fish is placed by M. Agassiz
in his family of ganoidians, termed _Scleroderms_; and he mentions
that another species has been found in the chalk of Westphalia. The
_Dercetis_ has a very elongated body, with a short head terminating in
a pointed beak; the upper jaw is a little longer than the lower, and
both jaws are armed with long, conical, elevated teeth, and several
rows of very small ones. On each side of the fish there are three rows
of osseous scutcheons like those of the Sturgeon (see _Wond._ p. 349);
the body was also covered with numerous small scales. From the form
of the body somewhat resembling that of the eel, being very long, and
sub-cylindrical in uncompressed examples, the specimens are generally
called "_petrified eels_" by the quarry-men. The examples usually found
consist of the elongated body, more or less compressed, and irregularly
covered with patches of scales confusedly intermingled; among which
traces of the scutcheons may sometimes be distinguished. These
specimens occasionally exceed two feet in length, by one or two inches
in breadth; with neither extremity perfect, and without any vestige
of the fins.[558] The example figured _Wond._ _Lign. 74_, is the only
instance in which I have seen the cranium perfect. The scutcheons in
the Westphalian species have a prominent longitudinal ridge or keel,
and their surface finely granulated; they are so large that the whole
body of the fish is covered with them.
[558] See _Foss. South D._ pl. xl. _fig._ 2, and pl. xxxiv. figs. 10
and 11.
[Sidenote: CTENOID FISHES.]
Fossil Ctenoid Fishes (_Poiss. Foss._ tom. iv.).--The fishes of this
order have imbricated laminated scales, the posterior margins of
which are round and finely pectinated; _i. e._ divided into little
teeth, like a comb. These scales are nearly circular, but more or less
elongated; and, as the laminæ of which they are composed successively
diminish from the lowermost to the uppermost, the pectinated margin of
each being apparent, the surface is very scabrous; the front edge is
sinuous. The common Perch is the type of the Ctenoidians. The teeth of
these fishes are invariably small, and either villous or brush-like.
From the numerous fossil genera I select, in illustration of the
characters of this order, the _Beryx_; of which four species occur
in the English Chalk, and three others in the Chalk of Bohemia and
Westphalia. Of this genus, which is closely related to the Perch
(_Perca_), two living species inhabit the seas of Australia. The bones
of the skull have dentated crests; the dorsal fin has spinous rays in
front, which are united to the soft rays; the margin of the caudal fin
has little spinous rays.
The Beryx is one of the most ancient representatives of the Perch
tribe, and of the Ctenoid order.
Beryx Lewesiensis.[559] _Wond._ p. 351; _Petrif._ _Lign. 90._--This
is one of the most common of the Ichthyolites of the Chalk of the
South-east of England; it is called "_Johnny Dory_" by the quarry-men;
the specimens are from six to twelve inches long. It occurs also in the
Chalk of Westphalia. The outline of the perfect form of this species,
_Wond._ p. 351, by Mr. Dinkel, conveys an accurate idea of its external
characters. It has one dorsal fin, with several spinous rays in front
of the soft ray. The head is very large, and the opercular pieces are
ornamented with sculptured rays; the margins of the jaws are covered
with a broad band of brush-teeth. The orbit is large, and often
contains the capsule (_sclerotica_) of the eye. The rays of the gills
are short and thick, five are preserved in some examples. The scales
are very large; about twenty-five in the median row; their posterior
margins have several concentric rows of spines (see _Lign. 185, fig.
3_, p. 567). The lateral line is often distinctly apparent, in the form
of a tube, contracted behind and expanded in the centre of the scale.
The vertebral column is composed of large short vertebræ, with very
long apophyses; the ribs are slight.
[559] The fossil discovered by me, and figured in _Foss. South D._ tab.
xxxvi. was the first perfect fish obtained from the Chalk. This fish
was first described by me, _Foss. South D._ tab. xxxv. xxxvi. as Zeus
_Lewesiensis_; M. Agassiz has very properly referred it to the genus
_Beryx_; but he has also substituted another specific name; which is
wholly unwarrantable, for that first imposed ought to be retained; see
p. 518, note.
Beryx superbus.--This is a larger species, sometimes thirteen inches
long, with very large and broad scales. It has been found in the lower
chalk at Lewes. See Dixon’s _Foss. Sussex_, tab. xxxvi. _fig._ 5.
Beryx radians. _Wond._ p. 350.--This species is smaller, and relatively
longer, than _B. Lewesiensis_; it generally occurs in the Chalk-marl,
and is invariably of a very dark colour, the scales having a polished
or glossy aspect. The scales are small, with a simple row of diverging
spines on the posterior edge. The scales of the lateral line are
peculiar; the mucous canal is not formed of a series of simple tubular
cylinders, as in _B. Lewesiensis_, but is divided into several
branches, as may be seen with a lens of moderate power. There are more
than thirty scales in the length of the lateral line.
Beryx microcephalus (_Poiss. Foss._ tom. iv. tab. iv^_c_.; and Dixon,
_Foss. Sussex_, tab. xxiv. _fig._ 3).--This fish is distinguished by
its slender form, and the extreme smallness of the head, as the name
implies. The scales have one row of very thick spines on the posterior
margin; they are more elevated, and shorter than in _B. radians_;
those of the lateral line are pierced by an elongated conical tube,
and are not ramified as in the last species. This ichthyolite, like
the _B. radians_, occurs in the Chalk-marl, and in a similar state of
mineralization.
Smerdis minutus. _Lign. 203._--A pretty ctenoidian fish, from one to
three inches long, about the dimensions of a perch a year old, is very
common in the marls of Aix in Provence, _Wond._ p. 260; and many are
often found grouped together in every variety of position. This species
is characterised by the elevated anterior rays of the dorsal, and the
wide and very forked caudal fin.
Several ctenoidian and cycloidian fishes have been found in the north
of the Brazils, by Mr. Gardiner, in strata probably of the Cretaceous
epoch.
Fossil Cycloid Fishes. (_Poiss. Foss._ tom. v.)--This order comprises
the fishes possessing scales of a cycloid, or circular, form, with
smooth margins, and composed of plates of horn or bone, without
enamel. It contains numerous families, including the _Scaroids_, or
Parrot-fishes, and the _Scomberoids_, or Mackerel tribe, which are
Acanthopterygians, the _Lucioids_, or Pikes, _Clupeoids_, or Herrings,
_Salmonoids_, or Salmon tribe, and the _Cyprinoids_, or Carps, which
are Malacopterygians, as well as other families. The fossil remains of
this order are exceedingly numerous, particularly in the Tertiary and
upper Secondary deposits. A genus of _Salmonidæ_, discovered in the
White Chalk of Sussex, will serve to exemplify the characters of the
fossil cycloidian fishes.
[Illustration: Lign. 203. Smerdis minutus. _Eocene._ (_nat. size_.)
_Aix in Provence._]
Osmeroides. _Plate II._ and _Wond._ p. 344, 347.--Two species of
this genus occur in the Chalk, near Lewes; and principally, if not
exclusively, in the Lower Chalk, without flints. They are exceedingly
beautiful Ichthyolites, and are almost invariably found with the body
but little compressed; the fish, in many examples, is as round and
perfect as when living. The entire cranium, the opercula and branchial
rays, and all the fins are preserved in some examples. These fishes
belong to the Salmon family,[560] and are nearly related to the Smelt
(_Osmerus_); whence the name of the genus. There are two species,
easily distinguishable. The first (_O. Mantelli_, _Pl. II._) has a
short, sub-cylindrical body, and seldom exceeds eight or nine inches in
length; the other (_O. Lewesiensis_) has an elongated and elliptical
body, and sometimes attains a length of fourteen inches. The dorsal fin
too in this species has more rays than in the other. The fossil figured
in _Pl. II_. is a very remarkable specimen of the first species. It
is nine inches in length; and the chalk has been cleared away, so as
to expose the entire fish, six inches in relief above the surface of
the block, _Petrif._ _Lign._ 92, p. 445. The fish is lying on its
back, with the mouth open, and the opercula, or gill-covers, and the
branchial arches expanded; the pectoral and ventral fins, and the
dorsal fin, are in their natural position; the five rays of the dorsal
are erect; of the caudal fin, or tail, but slight indications remain.
There is but one dorsal fin; but in a specimen of _O. Lewesiensis_
there is a trace of the little adipose process observable between the
dorsal fin and the tail, as in the recent species of _Salmonidæ_. A
magnified view of one of the scales is represented _Lign. 185, fig.
4_, p. 567.
[560] They were first described by me in _Foss. South D._ p. 235, tab.
xxxiii. and xl. as _Salmo Lewesiensis_.
Of the Cyprinoids, or fishes of the Carp family (Malacopterygians), the
recent species of which are inhabitants either of fresh-water, or the
brackish waters of the mouths of rivers, many fossil species occur in
the fluviatile and lacustrine deposits of the Tertiary formations. In
their character of omnivorous fishes, the Carps then, as now, formed
the principal mass of the finny population of the lakes, and in their
turn served as food to the carnivorous tribes, as the pikes, eels,
&c. Several species are found in a beautiful state in the schists of
Œningen, and in the Tertiary marls at Aix. Many of the layers of marl
at the latter locality are covered with groups of fishes of the family
_Cyprinodonts_, the recent species of which are of a small size, and
inhabit the fresh-water lakes of temperate zones. _Lign. 184_, p. 562,
represents a portion of a large slab of marl in the cabinet of Sir
R. Murchison, which is covered with scores of a species resembling a
recent fish (_Lebias_) in the profile of its head, and the form of its
fins. It is named Lebias cephalotes, from the relative largeness of its
head. The black appearance of the abdomen in many of these Ichthyolites
indicates the original situation of the intestines and of the liver,
which is largely developed in the fishes of this family, and contains
much colouring matter.
Saurocephalus and Saurodon. _Lign. 204._--In the same quarry, near
Lewes, from which the first entire fish of the Sussex Chalk was
obtained, teeth of a very peculiar character were, many years since,
occasionally discovered.[561] These teeth are of a lanceolate form,
much compressed; with entire, sharp edges, terminating in a point;
the fang is single, and broad; the surface of the crown is glossy,
and marked with fissures filled with chalk (see _Lign. 204, fig.
1_). Teeth of this kind, attached to portions of the jaw, were
subsequently found in the Chalk at Brighton and Lewes. Similar remains
were collected from the Cretaceous marls of Missouri and New Jersey,
in the United States. The American specimens comprised two closely
allied genera, which, from the supposition that the fossils were the
relics of reptiles, were respectively designated _Saurocephalus_ and
_Saurodon_.[562] Examples of the teeth and jaws of both genera have
been discovered in the Sussex Chalk (see _Lign. 204_).
[561] Foss. South D. tab. xxxiii. p. 228.
[562] American Phil. Trans, vol. iii. new series, pl. xvi. on the
Saurodon, by Dr. Hays; and Journal Acad. Sciences, Philadelphia, vol.
iii. on the _Saurocephalus_, by Dr. Harlan.
[Illustration: Lign. 204. Fossil Teeth and Jaws of Fishes. _Chalk._
_Sussex._]
Fig. 1.--Tooth of Saurocephalus lanciformis. _Lewes._
2.--Teeth of Saurocephalus striatus. _Brighton._
Portion of the jaw, with five teeth.
3.--Fragment of a jaw, with two perfect teeth, and the base
of another, of Saurodon Leanus. _Kemptown, Brighton._
4.--Enchodus halocyon. Left branch of the lower jaw,
with teeth; and one front tooth of the opposite portion.
_Lewes._
M. Agassiz retains the names imposed by the American naturalists, and
has placed these genera in the family of Scomberoids (_Mackerel_,
_Swordfish_). They belong to the _Pharyngognathi_ of Muller. The teeth
are disposed in a single row, and fixed in deep sockets by a simple
root, or fang, which is frequently somewhat excavated by the pressure
of a successional tooth. In _Saurodon Leanus_ the crown of the tooth is
angular, and barbed, and supported on a sub-cylindrical shank, or stem
(see _Lign. 204, fig. 3_). The microscopical structure of these teeth
presents that peculiar reticulated disposition of the medullary canals
throughout the entire body of the tooth, which is only found in the
dental organs of fishes.
Hypsodon Lewesiensis. (_Foss. South D._ tab. xlii.)--The Sussex
and Kentish Chalk also contain the remains of a very large fish,
belonging to the Pharyngognathi, with extremely upright, long, conical,
compressed, pointed teeth, which, like those of the Saurodon, are
implanted in sockets. These teeth are commonly of a delicate fawn
colour externally and of a dark brown internally; having a large simple
pulp-cavity. In _Foss. South D._ (tab. xlii.) are represented portions
of an intermaxillary and jaw-bone with teeth; a vertebra, deeply
biconcave; and a large bone, apparently a branch of the _os hyoides_;
all found in the same block of chalk.[563]
[563] A magnificent specimen (now in the British Museum) displays,
on the same slab of chalk, a large portion of the cranium, teeth,
several vertebræ, ribs, and many other bones, belonging to a fish of
considerable magnitude. _Petrif._ p. 444.
Enchodus (_sword-tooth_) halocyon. _Lign. 204, fig. 4._ (Poiss.
Foss. tom. v. tab. xxv^_c_.)--The specimen figured is a portion of
the lower jaw, with one row of elongated, conical, slightly curved,
pointed teeth; the two anterior teeth being much longer and larger
than the others; it affords a good illustration of the dental organs
of _Enchodus_; a genus of Acanthopterygian fishes, the jaws and teeth
of which are often found in the Sussex Chalk. The teeth are of various
sizes, and attached by anchylosis, one row on the premandibular bone,
and another irregular row of smaller teeth to the inside of the lower
jaw. The two anterior teeth are very large, and of a peculiar form:
their base is wide and solid, and the shank of the tooth is suddenly
contracted immediately above, and becomes elongated into a point. These
teeth are generally of a dark colour, have a glossy aspect, and are
very brittle; differing so remarkably in this respect from the shark’s
teeth, with which they are usually collocated, that mere fragments can
be readily identified. The external surface of the lower jaw is marked
with finely granulated, longitudinal ridges or striæ.[564]
[564] A fine example of the lower jaw, with twelve teeth, is figured
_Foss. South D._ tab. xli. and another, with the upper jaw and
teeth, _Geol. S. E._ p. 140. Beautiful figures of the remains of
Saurocephalus, Enchodus, Hypsodon, and many other fine Chalk fishes,
are given in Dixon’s _Fossils of Sussex_, 4to. 1850.
Mr. Toulmin Smith, of Highgate, has in his Museum a portion of the
lower jaw with fifteen teeth of a small individual, imbedded in the
centre of a flint nodule, from Gravesend, which was discovered by
accidentally breaking the stone. The bone of the jaw and the teeth are
of a dead white colour, and appear not to be in the slightest degree
silicified; but in those teeth which are broken the pulp-cavity is
filled with quartz, which must have transuded through the walls of the
teeth.
Ichthyolites of recent species.--The distinguished naturalist to
whose labours in fossil Ichthyology we have been so largely indebted,
states, that of the many hundred species submitted to his notice, but
one can be identified with any fish now living. This conclusion must,
however, be received with some reservation; for, among the fossil
genera, founded on the teeth, there are species which certainly cannot
be distinguished from recent forms. And in the diluvial drift at
Breslau, associated with the bones of the fossil elephant (_Elephas
primigenius_), the remains of a pike, closely resembling the common
European species, have lately been discovered.[565]
[565] Agassiz, _Poiss. Foss._ tom. v. p. 68.
The exception above alluded to, is a little Malacopterygian fish,
rather larger than a Sprat, called the Capelan (Mallotus villosus),
which inhabits the banks of Newfoundland, and other parts of the coasts
of the northern seas. Fossil specimens of this fish.[566] occur in
nodules of indurated marl or clay, on the coast of Greenland.[567] It
is supposed that these Ichthyolites are of very recent date: and that
similar fossils are in the progress of formation.
[566] See _Poiss. Foss._ tom. v. pl. lx., in which the skeleton of the
recent fish, and specimens of the fossil species, are represented.
[567] Similar fossils have been obtained from the "Drift" on the Saco
River, thirty miles north of Portsmouth, New Hampshire. See Lyell’s
Second Visit to the United States, vol. i. p. 29.
Ichthyopatolites, or imprints of the pectoral fin-rays of certain
fishes. Under this name Dr. Buckland described certain problematical
markings observed on a flag-stone from a coal-pit at Mostyn, in
Flintshire, and now in the Geological Society’s Museum. It consists of
curvilinear scratches or imprints, disposed symmetrically at regular
intervals on each side a smooth level space, about two inches wide,
which may correspond to the body of a fish, the pectoral fins of which
Dr. Buckland suggests were the instruments by which the markings in
question were formed.
These scratches follow each other in nearly equidistant rows of three
in a row, and at intervals of about two inches from the point of each
individual scratch to the points of those next succeeding and preceding
it; they are slightly convex outwards, three on each side the median
space, or supposed track of the body of the fish. Dr. Buckland, in
the memoir referred to, shows that these markings cannot be referable
to the imprint of the feet or claws of reptiles, and points out the
structure of the bony anterior rays of the pectoral fins, as in certain
Siluroid and Lophoid fishes, and in the Climbing Perch (_Anabas
scandens_), or the _Hassar_ (_Doras costata_), and refers also to the
ambulatory movements of the common Gurnard, in corroboration of this
opinion.[568]
[568] Proceedings of Geol. Society, vol. iv. p. 204.
* * * * *
_Geological Distribution of Fossil Fishes._--From the incidental
notices of the geological habitats of the fossil fishes enumerated in
our survey of this class of beings, the reader cannot fail to have
remarked, that the most recent strata abounded in forms related to the
inhabitants of the existing seas and rivers; while the most ancient
teemed with species and genera of families altogether extinct, or of
prodigious rarity in the recent fauna.
In general terms, it may be stated, upon the authority of M. Agassiz,
that the Ichthyolites of the Tertiary deposits approach in their
characters to the living genera, but all the species are extinct. The
newer Tertiary, as the Crag, contain genera common to tropical seas,
as the large sharks (_Carcharias_), and eagle-rays (_Myliobates_),
&c. In the Eocene, or most ancient Tertiary, as the London and Paris
basins, Monte Bolca, &c., many of the Ichthyolites are closely related
to recent genera. Of the Chalk fishes, a few only are of recent genera,
but the majority are still allied to Tertiary forms. In the Chalk,
the _Pharyngognathi_, _Acanthopteri_, and _Malacopteri_ are met with
as new types; and indications of the _Hybodontidæ_, _Sauroidei_, and
_Cœlacanthi_ (the last derived from the Devonian, and the other two
from the Carboniferous Limestone) appear for the last time.
The ichthyic fauna of the Cretaceous deposits is closely related by
the majority of its _family_ groups with that of the series of strata
from the Lias to the Wealden, inclusive. In and above the Lias all
the ganoid fishes are _homocercal_. Below the Lias, the genera and
species are far more removed from existing types, and almost all are
_heterocercal_.
Of the eight thousand living fishes known to naturalists, three-fourths
belong to the Cycloid and Ctenoid orders, and of these no species are
known below the Chalk; the other fourth is referable to the Placoids
and Ganoids, of which there are comparatively but few existing
species. Yet fishes of these two orders almost solely flourished
during the ancient Secondary formations; for below the Lias, the
predominant recent orders are altogether absent. Beneath the Coal,
true carnivorous fishes, with trenchant teeth, are almost unknown;
but omnivorous species, with either brush or obtusely conical teeth,
and great sauroid fishes, are the prevailing representatives of the
class.[569] In fine, the Ichthyolites of the different formations
constitute two grand groups, which have their boundary line at the base
of the Cretaceous deposits. The first and most ancient comprises the
Ganoids and Placoids; the second, more intimately related to existing
types, comprehends forms more diversified; these are principally
Ctenoid and Cycloid, with a small number of the two preceding orders,
which insensibly disappear; and their few living analogues are very
distinct from the ancient species. Now, although deductions of this
nature may require to be modified with the progress of knowledge,
yet the generalizations thus obtained are founded on so vast an
accumulation of facts and observations, as to render it improbable that
they will be materially invalidated by future discoveries; for they
remarkably accord with the results derived from the investigation of
the fossil remains of all the other classes of animals. The most modern
deposits contain the remains of animals allied to the existing species;
the most ancient, of forms altogether extinct, or of excessive rarity
in the recent faunas. The discovery of existing species, or genera, in
the most ancient strata, would modify, but not destroy, the inferences
deduced from the facts hitherto obtained; and every geologist is
prepared to find that such may be the case.
[569] In the several chapters on the different formations, as arranged
in the _Wonders_, the student will find succinct notices of the
distribution of the _genera_ of fishes throughout the fossiliferous
deposits. A list of the Chalk species known in 1848 is given at pp.
356-359, _Wond._
Thus of the Sharks, with triangular notched teeth, which are so common
in the Tertiary formations, and were formerly unknown in the ancient
Secondary, one representative has been found in the Carboniferous
system (see p. 595). But, if teeth of this type should hereafter be
discovered in every Secondary deposit, the great preponderance of these
fishes over the Sauroid in the Tertiary, and in the existing seas,
would not be the less remarkable.
* * * * *
On Collecting and Developing Fossil Fishes.--From what has been
advanced, the reader will have obtained a general knowledge of the
fossil remains of this class that are likely to be met with in
particular deposits. Thus, he will expect to find the teeth of large
sharks and rays in the Tertiary clays and sands; and skeletons and
perfect specimens of numerous Ctenoid and Cycloid fishes in the
laminated marls and fine limestones of the same formations. In the
Chalk, with numerous teeth of sharks, he may discover splendid examples
of Cycloid and Ctenoid fishes; and, in the Wealden, large Ganoidian
forms. Passing to the ancient Secondary strata, the extraordinary
buckler-headed and Sauroid fishes will arrest his attention; and
their vestiges will be found, more or less perfect, in the shales and
limestones, and in the indurated nodules of clay and sandstone.
The detached teeth of fishes in Tertiary sands and clays may be easily
obtained entire, and should be arranged in the same manner as the
shells (see p. 442), either in trays, or on boards. The triangular
teeth, with lateral denticles, must be carefully extracted, so as
to preserve those appendages on which the specific and generic
distinctions of many Ichthyolites depend. M. Agassiz particularly
recommends the preservation of all the specimens collected together in
the same locality, as many may probably belong to the same individual,
and thus the dental organization of the original be determined.
Teeth collected from the same stratum in different places, should
not, therefore, be mixed together. Several series of the same kind of
teeth should be preserved, and as many as possible of each kind; for
specimens apparently identical may prove to be highly instructive as a
series. I have often had occasion to regret the disposal of supposed
duplicates, in my earlier researches, which would have tended to
elucidate the characters of those specimens which were retained.
The Ichthyolites, and their detached teeth and fins, in the Chalk and
other soft limestones, may be cleared by means of a penknife or graver
and small sharp chisels. It is preferable to leave the teeth attached
to small blocks of the chalk; as in the examples, figured _Lign.
193_. But to develop the beautiful Chalk Ichthyolites, particularly
those of the Osmeroides, Macropoma, &c. some practice and considerable
dexterity are required. The compressed fishes, as the Beryx, like
those in the Tertiary limestones, often lie in the sedimentary plane
of the stone, and may be sufficiently exposed, by a blow of a hammer
or a pick, to show the nature of the fossil, and admit of being easily
developed. But the fishes with sub-cylindrical bodies very commonly
split asunder in a transverse direction: and those with spinous scales,
as the Macropoma, adhere so firmly to the chalk, that, to display the
external surface of their scales, the surrounding stone must be removed
piecemeal, in the manner described for the Chalk crustaceans (see p.
544). The collector who sees the splendid Chalk fishes in the British
Museum,[570] and learns that they were found in the Chalk of Kent and
Sussex, will be grievously disappointed, upon visiting the quarries
from which they were obtained, if he expects to discover specimens with
any considerable portion of the scales, or body, exposed. It was many
years before the quarry-men acquired the tact they now possess, of
detecting, from very slight evidence, the presence of an Ichthyolite
in a block of chalk: patches of scales, which the quarry-men called
"_bran_," and detached sharks’ teeth, "_birds beaks_," and "_snakes'
tongues_," and teeth of Ptychodus, "_slugs_," being the only remains of
fishes generally observed and laid aside by the workmen.
[570] _Petrifactions_, pp. 441, 444.
The fossil _Salmon_ or _Smelt_ (see p. 626), which may be considered
as one of the most extraordinary of the Chalk fishes found in England,
affords an excellent illustration of the mode of developing the
Ichthyolites of this formation. This interesting fossil is delineated
on a small scale, in three different states, in _Plate II._; and
affords a good practical lesson for the young collector. Among some
blocks of chalk which a recent fall in one of the quarries near Lewes
had brought to light, was a large mass split asunder, and exposing on
each corresponding surface an irregular oval marking of a yellowish
brown colour; this appearance is represented _Pl. II. _fig._ 1_.
Presuming that these markings were produced by a transverse section of
the body of a fish, the two blocks were trimmed into a portable size,
and accurately cemented together with very _hot, thin, fresh_ glue.
When consolidated, some of the chalk was chiselled off in the supposed
longitudinal direction of the enclosed fish, and part of the body,
covered with scales, was exposed, as _Pl. II. fig. 2_. With the view
of ascertaining the extent of the Ichthyolite, some of the surrounding
stone was then removed towards each extremity of the block, and traces
of the fish were discovered, as shown in the same figure. The task of
completely developing the fossil was thus rendered comparatively easy;
the chalk was chiselled, cut, and scraped away, till the perfect fish,
as seen in _fig._ 3, was developed.[571] The block was then reduced to
a convenient size, and the edges sawn smooth. The chalk is easily cut
with a carpenter’s saw; the instrument should be short and strong, and
the teeth of moderate size.
[571] The figure in _Pl. II._ is too small to convey an accurate
idea of this Ichthyolite, which is now in the British Museum; see
_Petrifactions_, pp. 445, 446. M. Agassiz’s figure very inaccurately
represents the original. A beautiful lithograph of this fish, by Mr.
Pollard, of Brighton, was published in the Catalogue of the Mantellian
Museum, 1836.
When a _portion_ of the body of an Ichthyolite of this kind is found in
a block of chalk, and the fracture of the block appears to be recent,
diligent search should be made for the corresponding piece; for it may
probably be found to contain the other part of the fish. A splendid
specimen of _Osmeroides Lewesiensis_, more than a foot long, was thus
obtained. The quarry-men, in a block of chalk which a recent fall had
thrown down, discovered a few inches of the caudal portion of the
body of a fish; on the broken surface of the stone, a section of the
body was distinctly seen, as in the specimen previously described.
Search was made among the fallen masses for the corresponding piece,
but without success. Upon observing the face of the quarry exposed by
the recent fall, on a projecting block, many yards above our reach, a
discoloured spot was indistinctly seen, and it was conjectured that
this might prove to be the other moiety of the Ichthyolite. The workmen
were directed to preserve this block if possible; but it remained _in
situ_ several months, and until the rock was again blasted; when the
stone so long coveted rolled away from the fallen mass, and fortunately
was soon discovered. It proved to be the corresponding portion of the
fish; with the head, opercula, branchial arches, pectoral fins, and
the anterior part of the body covered with beautiful cycloid scales.
In the preparation of fossils of this kind, glue as the cement, and a
paste made of plaster of Paris with thin glue, to fill up the crevices
and strengthen the block, are the materials I have employed. The fossil
remains of fishes in other rocks require to be extracted and developed
in the manner previously directed for the Echinoderms, Cephalopoda,
&c. (pp. 332, 497.)
The collector may be reminded, that _Otolithes_, or ear-stones (p.
574), are found in the Crag of Norfolk, and other Tertiary strata;
and that Coprolites, associated with minute scales, bones, &c. of
small fishes, constitute, in some localities, layers of considerable
thickness and of great extent. The "_bone-bed_" of the Lias, near
Westbury, and that of the Ludlow series on the banks of the Teme, near
Ludlow,[572] are well-known examples of such a deposit.
[572] See Mr. Strickland’s interesting notice of the distribution and
contents of this "bone-bed," in the Quart. Geol. Journ. vol. ix. p. 8
Microscopical Examination.--A few words on the microscopical
examination of the remains of fishes may be useful. The structure of
the large, and the forms of the minute scales, may be seen by a common
lens, and without preparing the specimens. But for the examination
of the intimate organization of scales, teeth, &c. the microscope is
required; and the method directed for the investigation of flint (p.
373) should be employed. The scales, portions of the membranes of
the air-bladder, stomach, &c. and thin chips of the teeth, rendered
temporarily transparent by oil of turpentine, or permanently so
by Canada balsam, should be viewed by transmitted light. But the
intricate structure of the dental organs, the medullary canals, and the
calcigerous tubes, cannot be successfully investigated without the aid
of the lapidary, or the adoption of the process described at page 67
for the preparation of fossil wood for microscopical examination.
BRITISH LOCALITIES OF FOSSIL FISHES.
⁂ The detached teeth, scales, vertebræ, &c. of fishes are so
extensively distributed, that there is scarcely a cliff or quarry
of fossiliferous rock in Great Britain, that does not contain some
examples. The following list of localities must, therefore, be
regarded as merely directing the student to a few places, in which
particular fossils of this class have been discovered.
Abergavenny. _Mt. L._ Teeth of _Psammodus_, _Orodus_, &c.
Armagh, Ireland. _Mt. L._ Numerous teeth and spines.
Arundel, Sussex. _Cret._ Quarries in the neighbourhood; beautiful
Chalk fishes.
Aust Cliff, near Westbury, Somersetshire. _Lower Lias._
_Pholidophorus_, &c. _Base of Lias._ In a layer called the bone-bed,
containing bones, scales, teeth, and Coprolites of fishes. Teeth of
_Ceratodus_, &c.
Axmouth. _Base of Lias: Bone-bed._ Numerous scales, bones, and teeth.
_Saurichthys_, &c.
Barrow-on-Soar. _Lias._ _Dapedius._
Bracklesham Bay, Sussex. _Eocene._ Magnificent specimens of Rays, as
_Myliobatis_, _Aëtobatis_, and of _Chimæroids_ were collected by the
late F. Dixon, Esq., and are now in the British Museum.
Brighton. Cret. Chalk quarries in the vicinity. _Beryx_, _Dercetis_,
_Saurocephalus_, _Saurodon_, and the common species of teeth, &c.
Bristol. _Mt. L._ The usual species of _Psammodus_, _Orodus_,
_Onchus_, &c.
Burdie-house, near Edinburgh. _Carb._ _Palæoniscus_, _Megalichthys_,
_Holoptychius_, &c.
Caithness, Scotland. _Old Red._ _Dipterus_, &c.
Charing, Kent. Many fishes in the Chalk.
Chatham, Kent. _Cret._ _Beryx_, _Hypsodon_, and the usual teeth, &c.
Cheltenham. _Base of Lias._ In the bone-bed teeth, scales, Coprolites.
Clayton, Sussex. _Lower Chalk._ _Beryx microcephalus_, and other rare
Ichthyolites.
Clifton, near Bristol. _Mt. L._ _Psammodus_, _Orodus_, &c.
Cromarty, Scotland. _Old Red._ _Coccosteus_, _Pterichthys_, &c.
Cuckfield, Sussex. _Wealden._ _Lepidotus, Hybodus, Acrodus._
Cullercoats, Durham. _Permian._ _Palæoniscus_, &c.
Dinton, Vale of Wardour. _Purbeck._ _Leptolepis_, _Ceramurus_, &c.
Downton Hall, near Ludlow. _Devonian._ _Cephalaspis_, _Dipterus_, &c.
_U. Sil._ In a quarry on the banks of the Teme, a fish-bed composed of
scales, teeth, and Coprolites, in Upper Ludlow limestone.
Dudley. _Sil._ _Ichthyodorulites_.
Dungannon, Ireland. _Permian._ Quarry at Rhone-hill; numerous small
_Palæonisci_, _P. catopterus_.
East Thickley, Durham. _Magnesian Limestone._ _Palæonisci._
Glammis, Forfarshire. _Devon._ _Cephalaspis, Gyrolepis, Dipterus._
Gravesend and Northfleet. Chalk-pits rich in fish-teeth, &c.
Hastings. _Wealden._ _Lepidotus, Hybodus._
Ilminster, Somerset. _Upper Lias._ _Pachycormus_ and _Leptolepis_.
Leeds, Middleton Quarry. _Carb._ Layers of _fish-coal_, abundance of
remains of _Megalichthys_, _Holoptychius_, &c. (_Geol. Proc._ iii. p.
153.)
Lewes, Sussex. _Cret._ All the fishes of the British Chalk. See
_Wond._ pp. 356-359.
Lyme Regis. _Lias._ _Dapedius_, _Hybodus_, _Squaloraia_; and numerous
other species and genera.
Newhaven, near Leith. _Carb._ On the shore, nodules of ironstone with
fishes and Coprolites. _Amblypterus, Palæoniscus._
Sheppey, Isle of. _Tert._ Numerous teeth of Rays, Sharks, &c., and
other Ichthyolites in great abundance.
Shotover, near Oxford. _Kimmeridge Clay._ _Ischyodus_, _Hybodus_, &c.
Southend, Essex. _Eocene._ Fish-bones and teeth (_Pisodus_, &c.) are
found on the shore along the foot of the cliff.
Speeton, Yorkshire. _Galt._ _Macropoma Egertoni_; and many other
fishes.
Steyning, Sussex. _Cret._ In the marl-pits, Coprolites and teeth of
Sharks are abundant.
Stonesfield. _Great Oolite._ _Hybodus_, _Lepidotus_, _Leptacanthus_,
&c.
Swanage. _Purbeck._ _Lepidotus_, _Hybodus_, _Ophiopsis_, &c.
Thurso, Scotland. _Devonian._ _Asterolepis_, &c.
Westbury, near Bristol. _Base of Lias._ Bone-bed with numerous remains.
Worthing. _Cret._ Beautiful Chalk fishes in the neighbouring quarries.
FOREIGN LOCALITIES.
⁂ Although the present work is expressly designed as a guide to
the British collector, I am induced to subjoin a few foreign localities
of Ichthyolites, that lie within the reach of the continental tourist.
A detailed account of the most celebrated sites is given by M. Agassiz,
Poiss. Foss.
Aix, in Provence. _Tertiary._ Some of the beds of gypseous marl
contain numerous species in abundance.
Eisleben, Upper Saxony. _Permian._ Numerous Ichthyolites in dark shale.
Glaris, Switzerland. _Cret._ Immense numbers of fishes in dark schist.
The specimens are often contorted, from the contraction of their
bodies, during decomposition.
Maestricht (St. Peter’s Mountain). _Upper Cret._ Numerous teeth,
vertebræ, &c. of fishes of the Cretaceous epoch. See _Wond._ p. 309.
Mansfeld, in Thuringia. Permian. Fishes in copper-slate, in great
numbers; many extremely beautiful.
Monte Bolca, or Vestena Nova. _Tert._ The richest mine of Ichthyolites
in the world. A catalogue of the numerous genera and species found
in this celebrated locality, is given in _Poiss. Foss._ tom. iv. pp.
33-52.[573] See _Wond._ p. 265.
Mount Lebanon, Asia. _Tert._ Numerous Ichthyolites, in great
perfection.
Œningen. _Tert. fresh-water._ Many kinds of fishes of the same genera
as those which inhabit the great European lakes; as the Perch, Salmon,
Eel, Pike, Carp, &c. A list of these Ichthyolites will be found in
_Poiss. Foss._ tom. ii. part ii. p. 78. See _Wond._ p. 263.
Saarbrück, in Lorraine. _Carb._ _Amblypterus_, and other Carboniferous
fishes.
Seefeld, in the Tyrol; on the principal road from Insbruck to Munich.
_Lias._ Abundance of fish in bituminous slate.
Stabia, Italy, at Torre d’Orlando, near Castellamare. _Oolite._
Beautiful fishes in fissile limestone.
Solenhofen. _Oolite._ Numerous Ichthyolites; many in great perfection.
See _Wond._ p. 513.
[573] It is necessary to caution the collector against the frauds
practised by the quarry-men, and dealers in fossils, at this and other
celebrated foreign localities. Specimens, apparently perfect, are
ingeniously constructed from the fragments of various examples. The
head of one fish, the body of another, decorated with the fins of a
third, and perhaps the tail of a fourth, of different species, or even
genera, are dove-tailed together, coloured, and varnished, so as to
deceive the common observer, and, occasionally, even the experienced
collector. Sponging the specimens with cold water will often detect the
imposition; for the colour if artificial will be removed, or rendered
paler, while the same process will heighten the natural tints. At
Pappenheim, Solenhofen, and other places, where fossil crustaceans, as
Shrimps, Prawns, &c. are found in such perfection, the imprints of good
specimens are often coloured, and offered for sale; a wet sponge will
speedily detect the imposture.
CHAPTER XVI.
FOSSIL REPTILES; COMPRISING THE ENALIOSAURIANS AND CROCODILES.
"Nous remontons done à un autre âge du monde; à cet âge où la terre
n’étoit encore parcourue que par des reptiles a sang froid--où la mer
abondoit en ammonites, en bélemnites, en térébratules, en encrinites,
et où tous ces genres, aujourd’hui d’une rareté prodigieuse, faisoient
le fond de sa population."--Cuvier, _Oss. Foss._ tom. v. p. 10.
We advance now to the investigation of the fossil remains of the more
highly organized classes of the Vertebrata; the Fishes being the
lowest in the scale amongst the beings characterised by an osseous
skeleton, with a flexible spinal column, composed of articulated bones,
and presenting, in the various classes, orders, genera, and species,
numerous modifications of form and structure. The mineralized relics
of the vertebrated animals consist, for the most part, of single and
displaced bones, or groups of bones and teeth, and the durable portions
of the dermal integuments; entire skeletons being of rare occurrence.
A knowledge of anatomy and physiology, and access to anatomical and
zoological libraries and collections, are therefore indispensable for
the cultivation of this most attractive department of Palæontology.
Fortunately for the English student, this branch of the science, which
a few years since was but little cultivated in this country,[574] has
been greatly advanced, by the liberal support afforded by the British
Association of Science to Professor Owen, whose Reports on the British
Fossil Reptiles and Mammalia, published in the Transactions of the
Association,[575] should be referred to for more precise and detailed
information than can be given in these unpretending volumes. Our
remarks will be limited to a general notice of the fossil remains of
Reptiles, Birds, and Mammals; with descriptions of such characteristic
examples, as will serve to illustrate the nature of the specimens that
may probably come under the notice of the collector; or which, from
their peculiar characters, are objects worthy his special attention.
[574] See _Petrif._ p. 226, note.
[575] Report of the Brit. Assoc. 1839 and 1841; see also Trans. Geol.
Soc. 2d ser. vol. v. p. 515 (1838).
The Age of Reptiles.[576]--The announcement by the illustrious founder
of Palæontology, in the quotation prefixed to this chapter, that there
was a period when the lakes, rivers, and seas of our planet were
peopled by reptiles, and when cold-blooded oviparous quadrupeds, of
appalling magnitude, were the principal inhabitants of the dry lands,
was a proposition so novel and startling, as to require the prestige
of the name of Cuvier to obtain for it any degree of credence, even
with those who were prepared to admit that a universal deluge could
not account for the physical changes, which the crust of the earth had
evidently undergone. Subsequent observations and discoveries have,
however, fully confirmed the truth of this induction, and the "_Age of
Reptiles_" is no longer considered fabulous.
[576] "_The Age of Reptiles_" was the title given by the author to
a popular summary of the evidence bearing on this question: it was
published in the Edinburgh Philosophical Journal, 1831. This name is
now generally employed to designate the geological epochs characterised
by the predominance of oviparous quadrupeds; namely, from the Permian
to the Chalk, inclusive.
In some of the ancient fossiliferous deposits,[577] indications of
the existence of Reptiles are visible, in the indelible markings left
by their footsteps on the muddy banks of rivers, and on the wet sands
of the sea-shores, now in the state of layers of marl and sandstone.
Here and there in the Devonian,[578] Carboniferous, and New Red
formations, teeth and bones are found, presenting unequivocal proofs
of the presence of extinct forms of cold-blooded oviparous quadrupeds.
As we ascend in the secondary formations, we are suddenly surrounded
by innumerable marine and terrestrial reptiles, belonging to species
and genera, and even orders, of which no living representatives are
known. Throughout the Liassic, Oolitic, Wealden, and Cretaceous epochs,
the class of Reptiles was at its fullest development. In the Tertiary
periods which succeeded, the Reptiles approach the recent types, and
their relics are found intermingled with the bones of mammiferous
quadrupeds; thus indicating the commencement of the present condition
and relations of the animal kingdom. Referring the reader to _Bd._ p.
165, and _Wond._ pp. 409-444 and 567-588, for a more comprehensive view
of this subject, we advance to the examination of some of the fossil
genera and species; and we propose, in the first place, to explain a
few essential characters of form and structure observable in those
durable parts of the skeletons which are most frequently met with in a
fossil state; namely, the teeth, jaws, vertebræ, &c., and the osseous
appendages of the dermal system.
[577] Devonian rooks of Elgin, North Britain; and the Lower
Carboniferous of Pottsville, Pennsylvania.
[578] The most ancient Reptile hitherto discovered is the _Telerpeton
Elginense_, from the Old Red of Scotland, which will be described in
the sequel.
The animals comprehended in the Class of Reptilia constitute, according
to Prof. Owen’s arrangement, eight principal groups, or Orders, as
follow:--
The _Batrachia_; Frogs: the body naked, }
with only rudimentary ribs; and with }
two or four feet. Most of these reptiles }
breathe by branchiæ or gills in their }
young state, and by lungs in the adult }
(as for example the Frog); in some (the }
_perenni-branchiata_), the branchiæ are }
persistent through life. } Having a tripartite
} heart (_i. e._ with
The _Ophidia_; Serpents: the body } two auricles and
destitute of feet. } one ventricle), and
} simple transverse
The _Lacertia_ or _Sauria_; Lizards: the } processes to the
body supported by four or two feet, and } cervical and anterior
covered with scales. } dorsal vertebræ.
}
The _Chelonia_; Tortoises: the body }
supported by four feet or paddles, and }
enveloped in two osseous bucklers, }
composed of the expanded bones of the }
sternum and thorax. }
The _Enaliosauria_; Sea-saurians }
(_extinct_): body furnished with four }
paddles, and destitute of scaly covering. }
}
The _Pterosauria_; Wing-saurians }
(_extinct_): body supported on four } Having a quadripartite
feet, the outer finger of each fore-foot } heart (_i. e._ with two
greatly lengthened, and forming a support } auricles and two
for the wing. } ventricles),and double
} transverse processes to
The _Crocodilia_; Crocodiles: body } the cervical and anterior
supported on four partially webbed feet, } dorsal vertebræ.
and encased with an armour of bony plates }
or scutes. }
}
The _Deinosauria_; Great-saurians }
(_extinct_): body supported on four feet. }
Teeth of Reptiles.--The teeth of the animals of this class exhibit
considerable diversity of form, but the characteristic type is that
of a conical, pointed tooth, with a simple root or fang; for, _in no
reptile does the base of the tooth terminate in more than one fang,
and this is never branched_. "Any fossil, therefore, which exhibits a
tooth implanted by two fangs in a double socket, must be mammiferous,
since the socketed teeth of reptiles have but a single fang; and the
only fishes’ teeth which approach such a tooth in form, are those of a
bifurcate base, belonging to certain sharks." (_Owen._)
These dental organs are only fitted for seizing and retaining the
prey or food; for no living reptiles have the power of performing
mastication. In the Crocodiles the tooth has a cylindrical shank,
with a conical, longitudinally striated, enamelled crown, having a
ridge on each side (_Pl. VI. fig. 5_). In the _Labyrinthodon_ (a
fossil reptile), the cone is more curved and pointed (_Pl. VI. fig.
3_); in the _Hylæosaurus_, the shank is cylindrical, and the crown
expanded and lanceolate, with blunt margins (_Pl. VI. fig. 6_); in
the _Megalosaurus_, the tooth is laterally compressed, trenchant, and
slightly inclined backwards like a sabre, with serrated edges (_Pl. VI.
fig. 7_); in the _Iguanodon_, the shank is cylindrical, and the crown
of a prismatic form, greatly expanded, with broad denticulated edges,
and longitudinal ridges on one side (_Pl. VI. fig. 4_, and _Ligns._
221, 223). In the Serpents, the teeth are very long and pointed; in the
Crocodiles and Lizards, may be seen every modification of the conical
form, down to a mere hemispherical tubercle or plate. In the fossil
_Dicynodon_, to be hereafter described, the dental system consists of
but two tusks or canine teeth, like those of the Walrus, implanted in
the upper jaw. The Turtles and some fossil Lacertians are edentulous,
_i. e._ destitute of teeth; their dental organs consisting of the horny
trenchant sheaths with which the jaws are covered.