THE TRIASSIC PERIOD.
We come now to the consideration of the great _Mesozoic_, or
Secondary series of formations, consisting, in ascending order,
of the Triassic, Jurassic, and Cretaceous systems. The Triassic
group forms the base of the Mesozoic series, and corresponds
with the higher portion of the New Red Sandstone of the older
geologists. Like the Permian rocks, and as implied by its name,
the _Trias_ admits of a subdivision into three groups--a Lower,
Middle, and Upper Trias. Of these sub-divisions the middle one
is wanting in Britain; and all have received German names, being
more largely and typically developed in Germany than in any other
country. Thus, the Lower Trias is known as the _Bunter Sandstein_;
the Middle Trias is called the _Muschelkalk_; and the Upper Trias
is known as the _Keuper_.
I. The lowest division of the Trias is known as the _Bunter
Sandstein_ (the _Grès bigarré_ of the French), from the generally
variegated colours of the beds which compose it (German, _bunt_,
variegated). The Bunter Sandstein of the continent of Europe
consists of red and white sandstones, with red clays, and thin
limestones, the whole attaining a thickness of about 1500 feet.
The term "marl" is very generally employed to designate the clays
of the Lower and Upper Trias; but the term is inappropriate, as
they may contain no lime, and are therefore not always genuine
marls. In Britain the Bunter Sandstein consists of red and mottled
sandstones, with unconsolidated conglomerates, or "pebble-beds,"
the whole having a thickness of 1000 to 2000 feet. The Bunter
Sandstein, as a rule, is very barren of fossils.
II. The Middle Trias is not developed in Britain, but it is largely
developed in Germany, where it constitutes what is known as the
_Muschelkalk_ (Germ. _Muschel_, mussel; _kalk_, limestone), from
the abundance of fossil shells which it contains. The Muschelkalk
(the _Calcaire coquillier_ of the French) consists of compact
grey or yellowish limestones, sometimes dolomitic, and including
occasional beds of gypsum and rock-salt.
III. The Upper Trias, or _Keuper_ (the _Marnes irisées_ of the
French), as it is generally called, occurs in England; but is
not so well developed as it is in Germany. In Britain, the Keuper
is 1000 feet or more in thickness, and consists of white and
brown sandstones, with red marls, the whole topped by red clays
with rock-salt and gypsum.
The Keuper in Britain is extremely unfossiliferous; but it passes
upwards with perfect conformity into a very remarkable group of
beds, at one time classed with the Lias, and now known under the
names of the Penarth beds (from Penarth, in Glamorganshire), the
Rhætic beds (from the Rhætic Alps), or the _Avicula contorta_ beds
(from the occurrence in them of great numbers of this peculiar
Bivalve). These singular beds have been variously regarded as the
highest beds of the Trias, or the lowest beds of the Lias, or as
an intermediate group. The phenomena observed on the Continent,
however, render it best to consider them as Triassic, as they
certainly agree with the so-called Upper St Cassian or Kössen
beds which form the top of the Trias in the Austrian Alps.
The Penarth beds occur in Glamorganshire, Gloucestershire,
Warwickshire, Staffordshire, and the north of Ireland; and they
generally consist of a small thickness of grey marls, white
limestones, and black shales, surmounted conformably by the lowest
beds of the Lias. The most characteristic fossils which they contain
are the three Bivalves _Cardium Rhoeticum, Avicula contorta_, and
_Pecten Valoniensis_; but they have yielded many other fossils,
amongst which the most important are the remains of Fishes and
small Mammals (_Microlestes_).
In the Austrian Alps the Trias terminates upwards in an extraordinary
series of fossiliferous beds, replete with marine fossils. Sir
Charles Lyell gives the following table of these remarkable
deposits:--
_Strata below the Lias in the Austrian Alps, in descending order._
/ Grey and black limestone, with calcareous
| marls having a thickness of about 50
| feet. Among the fossils, Brachiopoda
1. Koessen beds. | very numerous; some few species common
(Synonyms, Upper | to the genuine Lias; many peculiar.
St Cassian beds of < _Avicula contorta, Pecten Valoniensis_,
Escher and Merian.) | _Cardium Rhoeticum, Avicula_
| _inoequivalvis, Spirifer Münsteri_,
| Dav. Strata containing the above fossils
| alternate with the Dachstein beds, lying
\ next below.
/ White or greyish limestone, often in beds
| three or four feet thick. Total thickness
| of the formation above 2000 feet. Upper
| part fossiliferous, with some strata
2. Dachstein beds. < composed of corals (_Lithodendron_.)
| Lower portion without fossils. Among the
| characteristic shells are _Hemicardium_
| _Wulfeni, Megalodon triqueler_, and
\ other large bivalves.
/ Red, pink, or white marbles, from 800 to
| 1000 feet in thickness, containing more
| than 800 species of marine fossils, for
3. Hallstadt beds | the most part mollusca. Many species of
(or St Cassian). < _Orthoceras_. True _Ammonites_,
| besides _Ceratites_ and
| _Goniatites, Belemnites_ (rare),
| _Porcellia, Pleurotomania, Trochus_,
\ _Monotis salinaria_, &c.
/ A. Black and grey \ Among the fossils
4. A. Guttenstein beds. | limestone 150 feet | are _Ceratites_
B. Werfen beds, base | thick, alternating | _cassianus_,
of Upper Trias? | with the underlying | _Myacites_
Lower Trias of < Werfen beds. > _fassaensis_,
some geologists. | B. Red and green | _Naticella_
| shale and sandstone, | _costata_, &c.
\ with salt and gypsum./
In the United States, rocks of Triassic age occur in several
areas between the Appalachians and the Atlantic seaboard; but
they show no such triple division as in Germany, and their exact
place in the system is uncertain. The rocks of these areas consist
of red sandstones, sometimes shaly or conglomeratic, occasionally
with beds of impure limestone. Other more extensive areas where
Triassic rocks appear at the surface, are found west of the
Mississippi, on the slopes of the Rocky Mountains, where the
beds consist of sandstones and gypsiferous marls. The American
Trias is chiefly remarkable for having yielded the remains of a
small Marsupial (_Dromatherium_), and numerous footprints, which
have generally been referred to Birds (_Brontozoum_), along with
the tracks of undoubted Reptiles (_Otozoum, Anisopus_, &c.)
The subjoined section (fig. 139) expresses, in a diagrammatic
manner, the general sequence of the Triassic rocks when fully
developed, as, for example, in the Bavarian Alps:--
[Illustration: Fig. 139. GENERALIZED SECTION OF THE TRIASSIC ROCKS
OF CENTRAL EUROPE.]
With regard to the _life_ of the Triassic period, we have to
notice a difference as concerns the different members of the group
similar to that which has been already mentioned in connection
with the Permian formation. The arenaceous deposits of the series,
namely, resemble those of the Permian, not only in being commonly
red or variegated in their colour, but also in their conspicuous
paucity of organic remains. They for the most part are either
wholly unfossiliferous, or they contain the remains of plants or
the bones of reptiles, such as may easily have been drifted from
some neighbouring shore. The few fossils which may be considered
as properly belonging to these deposits are chiefly Crustaceans
(_Estheria_) or Fishes, which may well have lived in the waters
of estuaries or vast inland seas. We may therefore conclude,
with considerable probability, that the barren sandy and marly
accumulations of the Bunter Sandstein and Lower Keuper were not
laid down in an open sea, but are probably brackish-water deposits,
formed in estuaries or land-locked bodies of salt water. This at
any rate would appear to be the case as regards these members
of the series as developed in Britain and in their typical areas
on the continent of Europe; and the origin of most of the North
American Trias would appear to be much the same. Whether this view
be correct or not, it is certain that the beds in question were laid
down in _shallow_ water, and in the immediate vicinity of _land_,
as shown by the numerous drifted plants which they contain and
the common occurrence in them of the footprints of air-breathing
animals (Birds, Reptiles, and Amphibians). On the other hand, the
middle and highest members of the Trias are largely calcareous,
and are replete with the remains of undoubted marine animals. There
cannot, therefore, be the smallest doubt but that the Muschelkalk
and the Rhætic or Kössen beds were slowly accumulated in an open
sea, of at least a moderate depth; and they have preserved for
us a very considerable selection from the marine fauna of the
Triassic period.
[Illustration: Fig. 140.--_Zamia spiralis_, a living Cycad.
Australia.]
The _plants_ of the Trias are, on the whole, as distinctively
Mesozoic in their aspect as those of the Permian are Palæozoic.
In spite, therefore, of the great difficulty which is experienced
in effecting a satisfactory stratigraphical separation between
the Permian and the Trias, we have in this fact a proof that the
two formations were divided by an interval of time sufficient
to allow of enormous changes in the terrestrial vegetation of the
world. The _Lepidodendroids, Asterophyllites_, and _Annularioe_,
of the Coal and Permian formations, have now apparently wholly
disappeared: and the Triassic flora consists mainly of Ferns,
Cycads, and Conifers, of which only the two last need special
notice. The _Cycads_ (fig. 140) are true exogenous plants, which
in general form and habit of growth present considerable resemblance
to young Palms, but which in reality are most nearly related to
the Pines and Firs (_Coniferoe_). The trunk is unbranched, often
much shortened, and bears a crown of feathery pinnate fronds.
The leaves are usually "circinate"--they unroll in expanding,
like the fronds of ferns. The seeds are not protected by a
seed-vessel, but are borne upon the edge of altered leaves, or
are carried on the scales of a cone. All the living species of
Cycads are natives of warm countries, such as South America, the
West Indies, Japan, Australia, Southern Asia, and South Africa.
The remains of Cycads, as we have seen, are not known to occur
in the Coal formation, or only to a very limited extent towards
its close; nor are they known with certainty as occurring in
Permian deposits. In the Triassic period, however, the remains
of Cycads belonging to such genera as _Pterophyllum_ (fig. 141,
b), _Zamites_, and _Podozamites_ (fig. 141, c), are sufficiently
abundant to constitute quite a marked feature in the vegetation;
and they continue to be abundantly represented throughout the
whole Mesozoic series. The name "Age of Cycads," as applied to
the Secondary epoch, is therefore, from a botanical point of
view, an extremely appropriate one. The _Conifers_ of the Trias
are not uncommon, the principal form being _Veltzia_ (fig. 141,
a), which possesses some peculiar characters, but would appear
to be most nearly related to the recent Cypresses.
[Illustration: Fig. 141.--Triassic Conifers and Cycads. a, _Voltzia_
(_Schizoneura_) _heterophylla_, portion of a branch, Europe and
America; b, Part of the frond of _Pterophyllum Joegeri_, Europe;
c, Part of the frond of _Podozamites lanceolatus_, America.]
As regards the _Invertebrate animals_ of the Trias, our knowledge
is still principally derived from the calcareous beds which
constitute the centre of the system (the Muschelkalk) on the
continent of Europe, and from the St Cassain and Rhætic beds
still higher in the series; whilst some of the Triassic strata
of California and Nevada have likewise yielded numerous remains
of marine Invertebrates. The _Protozoans_ are represented by
_Foraminifera_ and _Sponges_, and the _Coelenterates_ by a small
number of _Corals_; but these require no special notice. It may be
mentioned, however, that the great Palæozoic group of the _Rugose_
corals has no known representative here, its place being taken
by corals of Secondary type (such as _Montlivaltia, Synastoea_,
&c.)
The _Echinoderms_ are represented principally by _Crinoids_,
the remains of which are extremely abundant in some of the
limestones. The best-known species is the famous "Lily-Encrinite"
(_Encrinus liliiformis_, fig. 142), which is characteristic of the
Muschelkalk. In this beautiful species, the flower-like head is
supported upon a rounded stem, the joints of which are elaborately
articulated with one another; and the fringed arms are composed
each of a double series of alternating calcareous pieces. The
Palæozoic Urchins, with their supernumerary rows of plates, the
Cystideans, and the Pentremites have finally disappeared; but
both Star-fishes and Brittle-stars continue to be represented.
One of the latter--namely, the _Aspidura loricata_ of Goldfuss
(fig. 143)--is highly characteristic of the Muschelkalk.
[Illustration: Fig. 142.--Head and upper part of the column of
_Encrinus liliiformis_. The lower figure shows the articulating
surface of one of the joints of the column. Muschelkalk, Germany.]
[Illustration: Fig. 143.--_Aspidura loricata_, a Triassic Ophiuroid.
Muschelkalk, Germany.]
The remains of _Articulate Animals_ are not very abundant in the
Trias, if we except the bivalved cases of the little Water-fleas
(_Ostracoda_), which are occasionally very plentiful. There are
also many species of the horny, concentrically-striated valves
of the _Estherioe_ (see fig. 122, b), which might easily be
taken for small Bivalve Molluscs. The "Long-tailed" Decapods
of the type of the Lobster, are not without examples but they
become much more numerous in the succeeding Jurassic period.
Remains of insects have also been discovered.
Amongst the _Mollusca_ we have to note the disappearance, amongst
the lower groups, of many characteristic Palæozoic types. Amongst
the _Polyzoans_, the characteristic "Lace-corals," _Fenestella,
Retepora_,[22] _Synocladia, Polypora_, &c., have become apparently
extinct. The same is true of many of the ancient types of
_Brachiopods_, and conspicuously so of the great family of the
_Productidoe_, which played such an important part in the seas
of the Carboniferous and Permian periods.
[Footnote 22: The genus _Retefora_ is really a recent one,
represented by living forms; and the so-called _Reteporoe_ of the
Palæozoic rocks should properly receive another name (_Phyllopora_),
as being of a different nature. The name _Retepora_ has been here
retained for these old forms simply in accordance with general
usage.]
[Illustraton: Fig. 144. Triassic Lamellibranchs. a, _Daonella_
(_Halobia_) _Lommelli_; b, _Pecten Valoniensis_; c, _Myophoria
lineata_; d. _Cardium Rhoeticum_; e. _Avicula contorta_; f. _Avicula
socialis_.]
_Bivalves_ (_Lamellibranchiata_) and _Univalves_ (_Gasteropoda_)
are well represented in the marine beds of the Trias, and some of the
former are particularly characteristic either of the formation as a
whole or of minor subdivisions of it. A few of these characteristic
species are figured in the accompanying illustration (fig. 144).
Bivalve shells of the genera _Daonella_ (fig. 144, a) and _Halobia_
(_Monotis_) are very abundant, and are found in the Triassic
strata of almost all regions. These groups belong to the family
of the Pearl-oysters (_Aviculidoe_), and are singular from the
striking resemblance borne by some of their included forms to
the _Strophomenoe amongst the Lamp-shells, though, of course, no
real relation exists between the two. The little Pearl-oyster,
_Avicula socialis_ (fig. 144, f), is found throughout the greater
part of the Triassic series, and is especially abundant in the
Muschelkalk. The genus _Myophoria_ (fig. 144, c), belonging
to the _Trigoniadoe_, and related therefore to the Permian
_Schizodus_, is characteristically Triassic, many species of the
genus being known in deposits of this age. Lastly, the so-called
"Rhætic" or "Kössen" beds are characterised by the occurrence
in them of the Scallop, _Pecten Valoniensis_ (fig. 144, b);
the small Cockle, _Cardium Rhoeticum_ (fig. 144, d); and the
curiously-twisted Pearl-oyster, _Avicula contorta_ (fig. 144,
e)--this last Bivalve being so abundant that the strata in
question are often spoken of as the "Avicula contorta beds."
[Illustration: Fig. 145.--_Ceratites nodosus_, viewed from the
side and from behind. Muschelkalk.]
Passing over the groups of the _Heteropods_ and _Pteropods_, we
have to notice the _Cephalopoda_, which are represented in the
Trias not only by the chambered shells of _Tetrabranchiates_, but
also, for the first time, by the internal skeletons of _Dibranchiate_
forms. The Trias, therefore, marks the first recognised appearance
of true Cuttle-fishes. All the known examples of these belong
to the great Mesozoic group of the _Belemnitidoe_; and as this
family is much more largely developed in the succeeding Jurassic
period, the consideration of its characters will be deferred till
that formation is treated of. Amongst the chambered _Cephalopods_
we find quite a number of the Palæozoic _Orthoceratites_, some of
them of considerable size, along with the ancient _Cyrtoceras_
and _Goniatites_; and these old types, singularly enough, occur
in the higher portion of the Trias (St Cassian beds), but have,
for some unexplained reason, not yet been recognised in the lower
and equally fossiliferous formation of the Muschelkalk. Along
with these we meet for the first time with true _Ammonites_,
which fill such an extensive place in the Jurassic seas, and
which will be spoken of hereafter. The form, however, which is
most characteristic of the Trias is _Ceratites_ (fig. 145). In
this genus the shell is curved into a flat spiral, the volutions of
which are in contact; and it further agrees with both _Goniatites_
and _Ammonites_ in the fact that the septa or partitions between
the air-chambers are not simple and plain (as in the _Nautilus_
and its allies), but are folded and bent as they approach the
outer wall of the shell. In the _Goniatite_ these foldings of
the septa are of a simply lobed or angulated nature, and in the
_Ammonite_ they are extremely complex; whilst in the _Ceratite_
there is an intermediate state of things, the special feature
of which is, that those foldings which are turned towards the
mouth of the shell are merely rounded, whereas those which are
turned away from the mouth are characteristically toothed. The
genus _Ceratites_, though principally Triassic, has recently
been recognised in strata of Carboniferous age in India.
From the foregoing it will be gathered that one of the most important
points in connection with the Triassic _Mollusca_ is the remarkable
intermixture of Palæozoic and Mesozoic types which they exhibit.
It is to be remembered, also, that this intermixture has hitherto
been recognised, not in the Middle Triassic limestones of the
Muschelkalk, in which--as the oldest Triassic beds with marine
fossils--we should naturally expect to find it, but in the St
Cassian beds, the age of which is considerably later than that
of the Muschelkalk. The intermingling of old and new types of
Shell-fish in the Upper Trias is well brought out in the annexed
table, given by Sir Charles Lyell in his 'Student's Elements of
Geology' (some of the less important forms in the table being
omitted here):--
GENERA OF FOSSIL MOLLUSCA IN THE ST CASSIAN AND HALLSTADT BEDS.
Common to | Characteristic of | Common to
Older Rocks. | Triassic Rocks | Newer Rocks.
| |
Orthoceras. | Ceratites. | Ammonites.
Bactrites. | Cochloceras. | Chemnitzia.
Macrocheilus. | Rhabdoceras. | Cerithium.
Loxonema. | Aulacoceras. | Monodonta.
Holopella. | Naticella. | Sphoera.
Murchisonia. | Platystoma. | Cardita.
Porcellia. | Halobia. | Myoconcha.
Athyris. | Hörnesia. | Hinnites.
Retzia. | Koninckia. | Monotis.
Cyrtina. | Scoliostoma. | Plicatula.
Euomphalus. | Myophoria. | Pachyrisma.
|(The last two are | Thecidium.
|principally but not |
|exclusively Triassic.)|
Thus, to emphasise the more important points alone, the Trias
has yielded, amongst the Gasteropods, the characteristically
Palæozoic _Loxonema, Holopella, Murchisonia, Euomphalus_, and
_Porcellia_, along with typically Triassic forms like _Platystoma_
and _Scoliostoma_, and the great modern groups _Chemnitzia_ and
_Cerithium_. Amongst the Bivalves we find the Palæozoic _Megalodon_
side by side with the Triassic _Halobia_ and _Myophoria_, these
being associated with the _Carditoe, Hinnites, Plicatuloe_, and
_Trigonioe_ of later deposits. The Brachiopods exhibit the Palæozoic
_Athyris, Retzia_, and _Cyrtina_, with the Triassic _Koninckia_
and the modern _Thecidium_. Finally, it is here that the ancient
genera _Orthoceras, Cyrtoceras_, and _Goniatites_ make their last
appearance upon the scene of life, the place of the last of these
being taken by the more complex and almost exclusively Triassic
_Ceratites_, whilst the still more complex genus _Ammonites_ first
appears here in force, and is never again wanting till we reach
the close of the Mesozoic period. The first representatives of
the great Secondary family of the _Belemnites_ are also recorded
from this horizon.
[Illustration: Fig. 146.--a, Dental plate of _Ceratodus serratus_,
Keuper; b, Dental plate of _Ceratodus altus_, Keuper; (After
Agassiz.)]
[Illustration: Fig 147.--_Ceratodus Fosteri_, the Australian
Mud-fish, reduced in size.]
Amongst the _Vertebrate Animals_ of the Trias, the _Fishes_ are
represented by numerous forms belonging to the _Ganoids_ and the
_Placoids_. The Ganoids of the period are still all provided
with unsymmetrical ("heterocercal") tails, and belong principally
to such genera as _Paloeoniscus_ and _Catopterus_. The remains of
Placoids are in the form of teeth and spines, the two principal
genera being the two important Secondary groups _Acrodus_ and
_Hybodus_. Very nearly at the summit of the Trias in England, in
the Rhætic series, is a singular stratum, which is well known as the
"bone-bed," from the number of fish-remains which it contains. More
interesting, however, than the above, are the curious palate-teeth
of the Trias, upon which Agassiz founded the genus _Ceratodus_.
The teeth of Ceratodus (fig. 146) are singular flattened plates,
composed of spongy bone beneath, covered superficially with a
layer of enamel. Each plate is approximately triangular, one
margin (which we now know to be the outer one) being prolonged
into prongs or conical prominences, whilst the surface is more or
less regularly undulated. Until recently, though the master-mind
of Agassiz recognised that these singular bodies were undoubtedly
the teeth of fishes, we were entirely ignorant as to their precise
relation to the animal, or as to the exact affinities of the fish
thus armed. Lately, however, there has been discovered in the
rivers of Queensland (Australia) a living species of _Ceratodus_
(_C. Fosteri_, fig. 147), with teeth precisely similar to those
of its Triassic predecessor; and we thus have become acquainted
with the use of these structures and the manner in which they
were implanted in the mouth. The palate carries two of these
plates, with their longer straight sides turned towards each
other, their sharply-sinuated sides turned outwards, and their
short straight sides or bases directed backwards. Two similar
plates in the lower jaw correspond to the upper, their undulated
surfaces fitting exactly to those of the opposite teeth. There
are also two sharp-edged front teeth, which are placed in the
front of the mouth in the upper jaw; but these have not been
recognised in the fossil specimens. The living _Ceratodus_ feeds
on vegetable matters, which are taken up or tom off from plants
by the sharp front teeth, and then partially crushed between
the undulated surfaces of the back teeth (Günther); and there
need be little doubt but that the Triassic _Ceratodi_ followed
a similar mode of existence. From the study of the living
_Ceratodus_, it is certain that the genus belongs to the same
group as the existing Mud-fishes (_Dipnoi_); and we therefore
learn that this, the highest, group of the entire class of Fishes
existed in Triassic times under forms little or not at all different
from species now alive; whilst it has become probable that the
order can be traced back into the Devonian period.
[Illustration: Fig. 148.--Footprints of a Labyrinthodont
(_Cheirotherium_), from the Triassic Sandstones of Hessberg, near
Hildburghausen, Germany, reduced one-eighth. The lower figure
shows a slab, with several prints, and traversed by reticulated
sun-cracks: the upper figure shows the impression of one of the
hind-feet, one-half of the natural size. (After Sickler.)]
[Illustration: Fig. 149.--Section of the tooth of _Labryinthodon
(Mastodonsaurus) Joegeri_, showing the microscopic structure.
Greatly enlarged. Trias.]
[Illustration: Fig. 150.--a, Skull of _Labyrinthodon Joegeri_,
much reduced in size; b, Tooth of the same. Trias Württemberg.]
The _Amphibians_ of the Trias all belong to the old order of
the _Labyrinthodonts_, and some of them are remarkable for their
gigantic dimensions. They were first known by their footprints,
which were found to occur plentifully in the Triassic sandstones
of Britain and the continent of Europe, and which consisted of
a double series of alternately-placed pairs of hand-shaped
impressions, the hinder print of each pair being much larger
than the one in front (fig. 148). So like were these impressions
to the shape of the human hand, that the at that time unknown
animal which produced them was at once christened _Cheirotherium_,
or "Hand-beast." Further discoveries, however, soon showed that
the footprints of _Cheirotherium_ were really produced by species
of Amphibians which, like the existing Frogs, possessed hind-feet
of a much larger size than the fore-feet, and to which the name
of _Labyrinthodonts_ was applied in consequence of the complex
microscopic structure of the teeth (fig. 149). In the essential
details of their structure, the Triassic Labyrinthodonts did not
differ materially from their predecessors in the Coal-measures
and Permian rocks. They possessed the same frog-like skulls (fig.
150), with a lizard-like body, a long tail, and comparatively
feeble limbs. The hind-limbs were stronger and longer than the
fore-limbs, and the lower surface of the body was protected by an
armour of bony plates. Some of the Triassic Labyrinthodonts must
have attained dimensions utterly unapproached amongst existing
Amphibians, the skull of _Labyrinthodon Joegeri_ (fig. 150) being
upwards of three feet in length and two feet in breadth. Restorations
of some of these extraordinary creatures have been attempted in
the guise of colossal Frogs; but they must in reality have more
closely resembled huge Newts.
Remains of _Reptiles_ are very abundant in Triassic deposits,
and belong to very varied types. The most marked feature, in
fact, connected with the Vertebrate fauna of the Trias, and of
the Secondary rocks in general, is the great abundance of Reptilian
life. Hence the Secondary period is often spoken of as the "Age
of Reptiles." Many of the Triassic reptiles depart widely in
their structure from any with which we are acquainted as existing
on the earth at the present day, and it is only possible here to
briefly note some of the more important of these ancient forms.
Amongst the group of the Lizards (_Lacertilia_), represented by
_Protorosaurus_ in the older Permian strata, three types more
or less certainly referable to this order may be mentioned. One
of these is a small reptile which was found many years ago in
sandstones near Elgin, in Scotland, and which excited special
interest at the time in consequence of the fact that the strata
in question were believed to belong to the Old Red Sandstone
formation. It is, however, now certain that the Elgin sandstones
which contain _Telerpeton Elginense_, as this reptile is termed,
are really to be regarded as of Triassic age. By Professor Huxley,
_Telerpeton_ is regarded as a Lizard, which cannot be considered
as "in any sense a less perfectly-organised creature than the
Gecko, whose swift and noiseless run over walls and ceilings
surprises the traveller in climates warmer than our own." The
"Elgin Sandstones" have also yielded another Lizard, which was
originally described by Professor Huxley under the name of
_Hyperodapedon_, the remains of the same genus having been
subsequently discovered in Triassic strata in India and South
Africa. The Lizards of this group must therefore have at one
time enjoyed a very wide distribution over the globe; and the
living _Sphenodon_ of New Zealand is believed by Professor Huxley
to be the nearest living ally of this family. The _Hyperodapedon_
of the Elgin Sandstones was about six feet in length, with limbs
adapted for terrestrial progression, but with the bodies of the
vertebræ slightly biconcave, and having two rows of palatal teeth,
which become worn down to the bone in old age. Lastly, the curious
_Rhynchosaurus_ of the Trias is also referred, by the eminent
comparative anatomist above mentioned, to the order of the Lizards.
In this singular reptile (fig. 151) the skull is somewhat bird-like,
and the jaws appear to have been destitute of teeth, and to have
been encased in a horny sheath like the beak of a Turtle or a
Bird. It is possible, however, that the palate was furnished
with teeth.
[Illustration: Fig. 151.--Skull of _Rhynchosaurus articeps_. Trias.
(After Owen.)]
The group of the Crocodiles and Alligators (_Crocadilia_),
distinguished by the fact that the teeth are implanted in distinct
sockets and the skin more or less extensively provided with bony
plates, is represented in the Triassic rocks by the _Stagonolepis_
of the Elgin Sandstones. The so-called "Thecodont" reptiles (such
as _Belodon, Thecodontosaurus_, and _Paloeosaurus_, fig. 152,
c, d, e) are also nearly related to the Crocodiles, though
it is doubtful if they should be absolutely referred to this
group. In these reptiles, the teeth are implanted in distinct
sockets in the jaws, their crowns being more or less compressed
and pointed, "with trenchant and finely serrate margins" (Owen).
The bodies of the vertebræ are hollowed out at both ends, but
the limbs appear to be adapted for progression on the land. The
genus _Belodon_ (fig. 152, c) is known to occur in the Keuper
of Germany and in America; and _Paloeosaurus_ (fig. 153. e)
has also been found in the Trias of the same region. Teeth of the
latter, however, are found, along with remains of _Thecodontosaurus_
(fig. 153, d), in a singular magnesian conglomerate near Bristol,
which was originally believed to be of Permian age, but which
appears to be undoubtedly Triassic.
[Illustration: Fig. 152.--Triassic Reptiles. a, Skull of
_Nothosaurus mirabilis_, reduced in size--Muschelkalk, Germany; b,
Tooth of _Simosaurus Gaillardoti_, of the natural size--Muschelkalk,
Germany; c, Tooth of _Beladon Carolinensis_--Trias, America; d,
Tooth of _Thecodontosaurus antiquus_, slightly enlarged--Britain;
e, Tooth of _Paloeosaurus platyodon_, of the natural
size--Britain.]
The Trias has also yielded the remains of the great marine reptiles
which are often spoken of collectively as the "Enaliosaurians"
or "Sea-lizards," and which will be more particularly spoken
of in treating of the Jurassic period, of which they are more
especially characteristic. In all these reptiles the limbs are
flattened out, the digits being enclosed in a continuous skin,
thus forming powerful swimming-paddles, resembling the "flippers"
of the Whales and Dolphins both in their general structure and
in function. The tail is also long, and adapted to act as a
swimming-organ; and there can be no doubt but that these
extraordinary and often colossal reptiles frequented the sea,
and only occasionally came to the land. The Triassic Enaliosaurs
belong to a group of which the later genus _Plesiosaurus_ is
the type (the _Sauropterygia_). One of the best known of the
Triassic genera is _Nothosaurus_ (fig. 152, a), in which the
neck was long and bird-like, the jaws being immensely elongated,
and carrying numerous powerful conical teeth implanted in distinct
sockets. The teeth in _Simosaurus_ (152, b) are of a similar
nature; but the orbits are of enormous size, indicating eyes of
corresponding dimensions, and perhaps pointing to the nocturnal
habits of the animal. In the singular _Placodus_, again, the
teeth are in distinct sockets, but resemble those of many fishes
in being rounded and obtuse (fig. 153), forming broad crushing
plates adapted for the comminution of shell-fish. There is a
row of these teeth all round the upper jaw proper, and a double
series on the palate, but the lower jaw has only a single row of
teeth. _Placodus_ is found in the Muschelkalk, and the characters
of its dental apparatus indicate that it was much more peaceful
in its habits than its associates the Nothosaur and Simosaur.
[Illustration: Fig. 153.--Under surface of the upper jaw and palate
of _Placodus gigas_. Muschelkalk, Germany.]
The Triassic rocks of South Africa and India have yielded the
remains of some extraordinary Reptiles, which have been placed by
Professor Owen in a separate order under the name of _Anomodontia_.
The two principal genera of this group are _Dicynodon_ and
_Oudenodon_, both of which appear to have been large Reptiles,
with well-developed limbs, organised for progression upon the
dry land. In _Oudenodon_ (fig. 154, B) the jaws seem to have
been wholly destitute of teeth, and must have been encased in
a horny sheath, similar to that with which we are familiar in
the beak of a Turtle. In _Dicynodon_ (fig. 154, A), on the other
hand, the front of the upper jaw and the whole of the lower jaw
were destitute of teeth, and the front of the mouth must have
constituted a kind of beak; but the upper jaw possessed on each
side a single huge conical tusk, which is directed downwards,
and must have continued to grow during the life of the animal.
[Illustration: Fig. 154.--Triassic Anomodont Reptiles. A, Skull
of _Dicynodon lacerticeps_, showing one of the great maxillary
tusks; B, Skull of _Oudenodon Bainii_, showing the toothless,
beak-like jaws. From the Trias of South Africa. (After Owen.)]
It may be mentioned that the above-mentioned Triassic sandstones
of South Africa have recently yielded to the researches of Professor
Owen a new and unexpected type of Reptile, which exhibits some
of the structural peculiarities which we have been accustomed
to regard as characteristic of the Carnivorous quadrupeds. The
Reptile in question has been named _Cyanodraco_, and it is looked
upon by its distinguished discoverer as the type of a new order,
to which he has given the name of _Theriodontia_. The teeth of
this singular form agree with those of the Carnivorous quadrupeds
in consisting of three distinct groups--namely, front teeth or
_incisors_, eye teeth or _canines_, and back teeth or _molars_.
The canines also are long and pointed, very much compressed, and
having their lateral margins finely serrated, thus presenting a
singular resemblance to the teeth of the extinct "Sabre-toothed
Tiger" (_Machairodus_). The bone of the upper arm (humerus) further
shows some remarkable resemblances to the same bone in the
Carnivorous Mammals. As has been previously noticed, Professor
Owen is of opinion that some of the Reptilian remains of the
Permian deposits will also be found to belong to this group of
the "Theriodonts."
[Illustration: Fig. 155.--Supposed footprint of a Bird, from
the Triassic Sandstones of the Connecticut River. The slab shows
also numerous "rain-prints."]
Lastly, we find in the Triassic rocks the remains of Reptiles
belonging to the great Mesozoic order of the _Deinosauria_. This
order attains its maximum at a later period, and will be spoken of
when the Jurassic and Cretaceous deposits come to be considered.
The chief interest of the Triassic Reptiles of this group arises
from the fact that they are known by their footprints as well as
by their bones; and a question has arisen whether the supposed
footprints of _birds_ which occur in the Trias have not really
been produced by Deinosaurs. This leads us, therefore, to speak
at the same time as to the evidence which we have of the existence
of the class of Birds during the Triassic period. No actual bones
of any bird have as yet been detected in any Triassic deposit;
but we have tolerably clear evidence of their existence at this
time in the form of _footprints_. The impressions in question
are found in considerable numbers in certain red sandstones of
the age of the Trias in the valley of the Connecticut River, in
the United States. They vary much in size, and have evidently been
produced by many different animals walking over long stretches of
estuarine mud and sand exposed at low water. The footprints now
under consideration form a double series of _single_ prints, and
therefore, beyond all question, are the tracks of a _biped_--that
is, of an animal which walked upon two legs. No living animals,
save Man and the Birds, walk habitually on two legs; and there
is, therefore, a _primâ facie_ presumption that the authors of
these prints were Birds. Moreover, each impression consists of
the marks of three toes turned forwards (fig. 155), and therefore
are precisely such as might be produced by Wading or Cursorial
Birds. Further, the impressions of the toes show exactly the
same numerical progression in the number of the joints as is
observable in living Birds--that is to say, the innermost of the
three toes consists of three joints, the middle one of four, and
the outer one of five joints. Taking this evidence collectively,
it would have seemed, until lately, quite certain that these
tracks could only have been formed by Birds. It has, however,
been shown that the Deinosaurian Reptiles possess, in some cases
at any rate, some singularly bird-like characters, amongst which
is the fact that the animal possessed the power of walking,
temporarily at least, on its hind-legs, which were much longer and
stronger than the fore-limbs, and which were sometimes furnished
with no more than three toes. As the bones and teeth of Deinosaurs
have been found in the Triassic deposits of North America, it
may be regarded as certain that _some_ of the bipedal tracks
originally ascribed to Birds must have really been produced by
these Reptiles. It seems at the same time almost a certainty
that others of the three-toed impressions of the Connecticut
sandstones were in truth produced by Birds, since it is doubtful
if the bipedal mode of progression was more than an occasional
thing amongst the Deinosaurs, and the greater number of the many
known tracks exhibit no impressions of fore-feet. Upon the whole,
therefore, we may, with much probability, conclude that the great
class of Birds (_Aves_) was in existence in the Triassic period.
If this be so, not only must there have been quite a number of
different forms, but some of them must have been of very large
size. Thus the largest footprints hitherto discovered in the
Connecticut sandstones are 22 inches long and 12 inches wide,
with a proportionate length of stride. These measurements indicate
a foot four times as large as that of the African Ostrich; and the
animal which produced them--whether a Bird or a Deinosaur--must
have been of colossal dimensions.
[Illustration: Fig. 156.--Lower jaw of _Dromatherium sylvestre_.
Trias, North Carolina. (After Emmons.)]
[Illustration: Fig. 157.--a, Molar tooth of _Micro estes antiquus_,
magnified; b, Crown of the same, magnified still further. Trias,
Germany.]
[Illustration: Fig. 158.--The Banded Ant-eater (_Myrmecobius
fasciatus_) of Australia.]
Finally, the Trias completes the tale of the great classes of the
Vertebrate sub-kingdom by presenting us with remains of the first
known of the true Quadrupeds or _Mammalia_. These are at present only
known by their teeth, or, in one instance, by one of the halves of
the lower jaw; and these indicate minute Quadrupeds, which present
greater affinities with the little Banded Anteater (_Myrmecobius
fasciatus_, fig. 158) of Australia than with any other living form.
If this conjecture be correct, these ancient Mammals belonged to
the order of the Marsupials or Pouched Quadrupeds (_Marsupialia_),
which are now exclusively confined to the Australian province,
South America, and the southern portion of North America. In the
Old World, the only known Triassic Mammals belong to the genus
_Microlestes_, and to the probably identical _Hypsiprymnopsis_ of
Professor Boyd Dawkins. The teeth of _Microlestes_ (fig. 157)
were originally discovered by Plieninger in 1847 in the "bone-bed"
which is characteristic of the summit of the Rhætic series both
in Britain and on the continent of Europe; and the known remains
indicate two species. In Britain, teeth of _Microlestes_ have been
discovered by Mr Charles Moore in deposits of Upper Triassic age,
filling a fissure in the Carboniferous limestone near Frome, in
Somersetshire; and a molar tooth of _Hypsiprymnopsis_ was found
by Professor Boyd Dawkins in Rhætic marls below the "bone-bed" at
Watchet, also in Somersetshire. In North America, lastly, there
has been found in strata of Triassic age one of the branches
of the lower jaw of a small Mammal, which has been described
under the name of _Dromatherium sylvestre_ (fig. 156). The fossil
exhibits ten small molars placed side by side, one canine, and
three incisors, separated by small intervals, and it indicates
a small insectivorous animal, probably most nearly related to
the existing _Myrmecobius_.
LITERATURE.
The following list comprises a few of the more important sources of
information as to the Triassic strata and their fossil contents:--
(1) 'Geology of Oxford and the Valley of the Thames.' Phillips.
(2) 'Memoirs of the Geological Survey of Great Britain and Ireland.'
(3) 'Report on the Geology of Londonderry,' &c. Portlock.
(4) "On the Zone of Avicula contorta," &c.--'Quart. Journ. Geol.
Soc.,' vol. xvi., 1860. Dr Thomas Wright.
(5) "On the Zones of the Lower Lias and the Avicula contorta
Zone"--'Quart. Journ. Geol. Soc.,' vol. xvii., 1861. Charles
Moore.
(6) "On Abnormal Conditions of Secondary Deposits," &c.--'Quart.
Journ. Geol. Soc.,' vol. xxiii., 1876-77. Charles Moore.
(7) 'Geognostische Beschreibung des Bayerischen Alpengebirges.'
Gümbel.
(8) 'Lethæa Rossica.' Pander.
(9) 'Lethæa Geognostica.' Bronn.
(10) 'Petrefacta Germaniæ.' Goldfuss.
(11) 'Petrefaktenkunde.' Quenstedt.
(12) 'Monograph of the Fossil Estheriæ' (Palæontographical Society).
Rupert Jones.
(13) "Fossil Remains of Three Distinct Saurian Animals, recently
discovered in the Magnesian Conglomerate near Bristol"--'Trans.
Geol. Soc.,' ser. 2, vol. v., 1840. Riley and Stutchbury.
(14) 'Die Saurier des Muschekalkes.' Von Meyer.
(15) 'Beiträge zur Palæontologie Württembergs.' Von Meyer and
Plieninger.
(16) 'Manual of Palæontology.' Owen.
(17) 'Odontography:' Owen.
(18) 'Report on Fossil Reptiles' (British Association, 1841). Owen.
(19) "On Dicynodon"--'Trans. Geol. Soc.,' vol. iii., 1845. Owen.
(20) 'Descriptive Catalogue of Fossil Reptilia and Fishes in the
Museum of the Royal College of Surgeons, England.' Owen.
(21) "On Species of Labyrinthodon from Warwickshire"--'Trans. Geol.
Soc.,' ser. 2, vol. vi. Owen.
(22) "On a Carnivorous Reptile" (Cynodraco major), &c.--'Quart.
Journ. Geol. Soc.,' vol. xxxii., 1876. Owen.
(23) "On Evidences of Theriodonts in Permian Deposits," &c.--'Quart.
Journ. Geol. Soc.,' vol. xxxii., 1876. Owen.
(24) "On the Stagonolepis Robertsoni," &c.--'Quart. Journ. Geol.
Soc.,' vol. xv., 1859. Huxley.
(25) "On a New Specimen of Telerpeton Elginense"--'Quart. Journ.
Geol. Soc.,' vol. xxiii., 1866. Huxley.
(26) "On Hyperodapedon"--'Quart. Journ. Geol. Soc.,' vol. xxv.,
1869. Huxley.
(27) "On the Affinities between the Deinosaurian Reptiles and
Birds"--'Quart. Journ. Geol. Soc.,' vol. xxvi., 1870. Huxley.
(28) "On the Classification of the Deinosauria," &c.--'Quart. Journ.
Geol. Soc.,' vol. xxvi., 1870. Huxley.
(29) "Palæontologica Indica"--'Memoirs of the Geol. Survey of India.'
(30) "On the Geological Position and Geographical Distribution of the
Dolomitic Conglomerate of the Bristol Area"--'Quart. Journ.
Geol. Soc.,' vol. xxvi., 1870. R. Etheridge, sen.
(31) "Remains of Labyrinthodonta from the Keuper Sandstone of
Warwick"--'Quart. Journ. Geol. Soc.,' vol. xxx., 1874 Miall.
(32) 'Manual of Geology.' Dana.
(33) 'Synopsis of Extinct Batrachia and Reptilia of North America.'
Cope.
(34) 'Fossil Footmarks.' Hitchcock.
(35) 'Ichnology of New England.' Hitchcock.
(36) 'Traité de Paléontologie Végétale.' Schimper.
(37) 'Histoire des Végétaux Fossiles.' Brongniart.
(38) 'Monographie der Fossilen Coniferen.' Goeppert.