is an English provincial name given to an argillaceous limestone, which,
with marl and clay, forms the base of the Jurassic formation, and passes
almost imperceptibly into the Lower Oolite in some places, where the
Marlstone of the Lias partakes of the mineral character, as well as the
fossil remains of the Lower Oolite; and it is sometimes treated of as
belonging to that formation. “Nevertheless, the Lias may be traced
throughout a great part of Europe as a separate and independent group,
of considerable thickness, varying from 500 to 1,000 feet, containing
many peculiar fossils, and having a very uniform lithological
aspect.”[61] The rocks which represent the Liassic period form the base
of the Jurassic system, and have a mean thickness of about 1,200 feet.
In the inferior part we find argillaceous sandstones, which are called
the sandstones of the Lias, and comprehend the greater part of the
_Quadersandstein_, or building-stone of the Germans, above which comes
compact limestone, argillaceous, bluish, and yellowish; finally, the
formation terminates in the marlstones which are sometimes sandy, and
occasionally bituminous.
[61] Lyell, “Elements of Geology,” p. 413.
The Lias, in England, is generally in three groups: 1, the upper, clays
and shales, underlying sands; 2, the middle, lias or marlstone; and 3,
the lower, clays and limestone; but these have been again
sub-divided--the last into six zones, each marked by its own peculiar
species of Ammonites; the second into three zones; the third consists of
clay, shale, and argillaceous limestone. For the purposes of description
we shall, therefore, divide the Lias into these three groups:--
1. _Upper Lias Clay_, consists of blue clay, or shale, containing
nodular bands of claystones at the base, crowded with _Ammonites
serpentinus_, _A. bifrons_, _Belemnites_, &c.
2. The _Middle Lias_, commonly known as the Marlstone, is surmounted by
a bed of oolitic ironstone, largely worked in Leicestershire and in the
north of England as a valuable ore of iron. The underlying marls and
sands, the latter of which become somewhat argillaceous below, form beds
from 200 to 300 feet thick in Dorsetshire and Gloucestershire; the
fossils are _Ammonites margaritaceus_, _A. spinatus_, _Belemnites
tripartitus_. The upper rock-beds, especially the bed of ironstone on
the top, is generally remarkably rich in fossils.
[Illustration: Fig. 88.--Gryphæa incurva.]
3. _Lower Lias_ (averaging from 600 to 900 feet in thickness) consists,
in the lower part, of thin layers of bluish argillaceous limestone,
alternating with shales and clays; the whole overlaid by the blue clay
of which the lower member of the Liassic group usually consists. This
member of the series is well developed in Yorkshire, at Lyme Regis and
Charmouth in Dorsetshire, and generally over the South-West and Midland
Counties of England. _Gryphæa incurva_ (Fig. 88), with sandy bands,
occurs at the base, in addition to which we find _Ammonites planorbis
Bucklandi_, _A. Ostrea liassica_, _Lima gigantea_, _Ammonites
Bucklandi_, &c., in the lower limestones and shales.
Above the clay are yellow sands from 100 to 200 feet thick, underlying
the limestone of the Inferior Oolite. These sands were, until lately,
considered to belong to the latter formation--as they undoubtedly do
physically--until they were shown, by Dr. Thomas Wright, of Cheltenham,
to be more nearly allied, by their fossils, to the Lias below than to
the Inferior Oolite above, into which they form the passage-beds.
In France the Lias abounds in the Calvados, in Burgundy, Lorraine,
Normandy, and the Lyonnais. In the Vosges and Luxembourg, M. Elie de
Beaumont states that the Lias containing _Gryphæa incurva_ and _Lima
gigantea_, and some other marine fossils, becomes arenaceous; and around
the Harz mountains, in Westphalia and Bavaria, in its lower parts the
formation is sandy, and is sometimes a good building-stone.
“In England the Lias constitutes,” says Professor Ramsay, “a
well-defined belt of strata, running continuously from Lyme Regis, on
the south-west, through the whole of England, to Yorkshire on the
north-east, and is an extensive series of alternating beds of clay,
shale, and limestone, with occasional layers of jet in the upper part.
The unequal hardness of the clays and limestones of the Liassic strata
causes some of its members to stand out in the distinct minor
escarpments, often facing the west and north-west. The Marlstone forms
the most prominent of these, and overlooks the broad meadows of the
lower Lias-clay, that form much of the centre of England.” In Scotland
there are few traces of the Lias. Zoophytes, Mollusca, and Fishes of a
peculiar organisation, but, above all, Reptiles of extraordinary size
and structure gave to the sea of the Liassic period an interest and
features quite peculiar. Well might Cuvier exclaim, when the drawings of
the Plesiosaurus were sent to him: “Truly this is altogether the most
monstrous animal that has yet been dug out of the ruins of a former
world!” In the whole of the English Lias there are about 243 genera, and
467 species of fossils. The whole series has been divided into zones
characterised by particular Ammonites, which are found to be limited to
them, at least locally.
Among the Echinodermata belonging to the Lias we may cite _Asterias
lumbricalis_ and _Palæocoma Furstembergii_, which constitutes a genus
not dissimilar to the star-fishes, of which its radiated form reminds
us. The Pentacrinites, of which _Pentacrinites Briareus_ is a type,
ornaments many collections by its elegant form, and is represented in
Figs. 79 and 89. It belongs to the order of Crinoidea, which is
represented at the present time by a single living species, _Pentacrinus
caput-Medusæ_, one of the rare and delicate Zoophytes of the Caribbean
sea.
Oysters (_Ostrea_) made their appearance in the Muschelkalk of the last
period, but only in a small number of species; they increased greatly in
importance in the Liassic seas.
[Illustration: Fig. 89.--Pentacrinites Briareus. Half natural size.]
The _Ammonites_, a curious genus of Cephalopoda, which made their first
appearance in small numbers towards the close of the preceding Triassic
period, become quite special in the Secondary epoch, with the close of
which they disappear altogether. They were very abundant in the Jurassic
period, and, as we have already said, each zone is characterised by its
peculiar species. The name is taken from the resemblance of the shell to
the ram’s-horn ornaments which decorated the front of the temple of
Jupiter Ammon and the bas-reliefs and statues of that pagan deity. They
were Cephalopodous Mollusca with circular shells, rolled upon themselves
symmetrically in the same plane, and divided into a series of chambers.
The animal only occupied the outer chamber of the shell; all the others
were empty. A siphon or tube issuing from the first chamber traversed
all the others in succession, as is seen in all the Ammonites and
Nautili. This tube enabled the animal to rise to the surface, or to sink
to the bottom, for the Ammonite could fill the chambers with water at
pleasure, or empty them, thus rendering itself lighter or heavier as
occasion required. The Nautilus of our seas is provided with the same
curious organisation, and reminds us forcibly of the Ammonites of
geological times.
Shells are the only traces which remain of the Ammonites. We have no
exact knowledge of the animal which occupied and built them. The attempt
at restoration, as exhibited in Fig. 91, will probably convey a fair
idea of the Ammonite when living. We assume that it resembled the
Nautilus of modern times. What a curious aspect these early seas must
have presented, covered by myriads of these Molluscs of all sizes,
swimming about in eager pursuit of their prey!
The Ammonites of the Jurassic age present themselves in a great variety
of forms and sizes; some of them of great beauty. _Ammonites bifrons_,
_A. Noditianus_, _A. bisulcatus_, _A. Turneri_ (Fig. 90), and _A.
margaritatus_, are forms characteristic of the Lias.
[Illustration: Fig. 90.--Ammonites Turneri, from the Lower Lias.]
The _Belemnites_, molluscous Cephalopods of a very curious organisation,
appeared in great numbers, and for the first time, in the Jurassic seas.
Of this Mollusc we only possess the fossilised internal “bone,”
analogous to that of the modern cuttle-fish and the calamary of the
present seas. This simple relic is very far from giving us an exact idea
of what the animal was to which the name of Belemnite has been given
(from Βελεμνον, _a dart_) from their supposed resemblance to the head of
a javelin. The slender cylindrical bone, the only vestige remaining to
us, was merely the internal skeleton of the animal. When first
discovered they were called, by the vulgar, “Thunder-stones” and
“Ladies’ fingers.” They were, at last, inferred to be the shelly
processes of some sort of ancient cuttle-fish. Unlike the Ammonite,
which floated on the surface and sunk to the bottom at pleasure, the
Belemnite, it has been thought, swam nearer the bottom of the sea, and
seized its prey from below.
[Illustration: Fig. 91.--Ammonite restored.]
[Illustration: Fig. 92.--Belemnite restored.]
In Fig. 92 is given a restoration of the living Belemnite, by Dr.
Buckland and Professor Owen, in which the terminal part of the animal is
marked in a slightly darker tint, to indicate the place of the bone
which alone represents in our days this fossilised being. A sufficiently
exact idea of this Mollusc may be arrived at from the existing
cuttle-fish. Like the cuttle-fish, the Belemnite secreted a black
liquid, a sort of ink or sepia; and the bag containing the ink has
frequently been found in a fossilised state, with the ink dried up, and
elaborate drawings have been made with this fossil pigment.
The beaks, or horny mandibles of the mouth, which the Belemnite
possessed in common with the other naked Cephalopoda, are represented in
Fig. 78, p. 181.
As Sir H. De la Beche has pointed out, the destruction of the animals
whose remains are known to us by the name of Belemnites was exceedingly
great when the upper part of the Lias of Lyme Regis was deposited.
Multitudes seem to have perished almost simultaneously, and millions are
entombed in a bed beneath Golden Cap, a lofty cliff between Lyme Regis
and Bridport Harbour, as well as in the upper Lias generally.[62]
[62] De la Beche’s “Geological Manual,” 3rd ed., p. 447.
Among the Belemnites characteristic of the Liassic period may be cited
_B. acutus_ (Fig. 93), _B. pistiliformis_, and _B. sulcatus_.
[Illustration: Fig. 93.--Belemnites acutus.]
The seas of the period contained a great number of the fishes called
_Ganoids_; which are so called from the splendour of the hard and
enamelled scales, which formed a sort of defensive armour to protect
their bodies. _Lepidotus gigas_ was a fish of great size belonging to
this age. A smaller fish was the _Tetragonolepis_, or _Æchmodus Buchii_.
The _Acrodus nobilis_, of which the teeth are still preserved, and
popularly known by the name of _fossil leeches_, was a fish of which an
entire skeleton has never been met with. Neither are we better informed
as to the _Hybodus reticulatus_. The bony spines, which form the
anterior part of the dorsal fin of this fish, had long been an object of
curiosity to geologists, under the general name of _Ichthyodorulites_,
before they were known to be fragments of the fin of the _Hybodus_. The
Ichthyodorulites were supposed by some naturalists to be the jaw of some
animal--by others, weapons like those of the living _Balistes_ or
_Silurus_; but Agassiz has shown them to be neither the one nor the
other, but bony spines on the fin, like those of the living genera of
_Cestracions_ and _Chimæras_, in both of which the concave face is armed
with small spines like those of the _Hybodus_. The spines were simply
imbedded in the flesh, and attached to it by strong muscles. “They
served,” says Dr. Buckland, “as in the _Chimæra_, to raise and depress
the fin, their action resembling that of a movable mast lowering
backward.”
[Illustration: Fig. 94.--Ichthyosaurus communis.]
Let us hasten to say, however, that these are not the beings that
characterised the age, and were the salient features of the generation
of animals which existed during the Jurassic period. These
distinguishing features are found in the enormous reptiles with lizard’s
head, crocodile’s conical teeth, the trunk and tail of a quadruped,
whale-like paddles, and the double-concave vertebræ of fishes; and this
strange form, on such a gigantic scale that even their inanimate remains
are examined with a curiosity not unmixed with awe. The country round
Lyme Regis, in Dorsetshire, has long been celebrated for the curious
fossils discovered in its quarries, and preserved in the muddy
accumulations of the sea of the Liassic period. The country is
hilly--“up one hill and down another,” is a pretty correct provincial
description of the walk from Bridport to Lyme Regis--where some of the
most frightful creatures the living world has probably ever beheld,
sleep the sleep of stones. The quarries of Lyme Regis form the cemetery
of the Ichthyosauri; the sepulchre where lie interred these dragons of
the ancient seas.
In 1811 a country girl, who made her precarious living by picking up
fossils for which the neighbourhood was famous, was pursuing her
avocation, hammer in hand, when she perceived some bones projecting a
little out of the cliff. Finding, on examination, that it was part of a
large skeleton, she cleared away the rubbish, and laid bare the whole
creature imbedded in the block of stone. She hired workmen to dig out
the block of Lias in which it was buried. In this manner was the first
of these monsters brought to light: “a monster some thirty feet long,
with jaws nearly a fathom in length, and huge saucer-eyes; which have
since been found so perfect, that the petrified lenses have been split
off and used as magnifiers,” as a writer in _All the Year Round_ assures
us.
[Illustration: Fig. 95.--Head of Ichthyosaurus platydon.]
In Fig. 95 the head of _I. platydon_ is represented. As in the Saurians,
the openings of the nostrils are situated near the anterior angle of the
orbits of the eyes, while those of the Crocodile are near the snout;
but, on the other hand, in its osteology and its mode of dentition it
nearly resembles the Crocodile; the teeth are pointed and conical--not,
however, set in deep or separate sockets, but only implanted in a long
and deep continuous groove hollowed in the bones of the jaw. These
strong jaws have an enormous opening; for, in some instances, they have
been found eight feet in length and armed with 160 teeth. Let us add
that teeth lost through the voracity of the animal, or in contests with
other animals, could be renewed many times; for, at the inner side of
the base of every old tooth, there is always the bony germ of a new one.
The eyes of this marine monster were much larger than those of any
animal now living; in volume they frequently exceed the human head, and
their structure was one of their most remarkable peculiarities. In front
of the sclerotic coat or capsule of the eye there is an annular series
of thin bony plates, surrounding the pupil. This structure, which is now
only met with in the eyes of certain turtles, tortoises, and lizards,
and in those of many birds, could be used so as to increase or diminish
the curvature of the transparent cornea, and thus increase or diminish
the magnifying power, according to the requirements of the
animal--performing the office, in short, of a telescope or microscope at
pleasure. The eyes of the Ichthyosaurus were, then, an optical apparatus
of wonderful power and of singular perfection, enabling the animal, by
their power of adaptation and intensity of vision, to see its prey far
and near, and to pursue it in the darkness and in the depths of the sea.
The curious arrangement of bony plates we have described furnished,
besides, to its globular eye, the power necessary to bear the pressure
of a considerable weight of water, as well as the violence of the waves,
when the animal came to the surface to breathe, and raised its head
above the waves. This magnificent specimen of the fish-lizard, or
Ichthyosaurus, as it was named by Dr. Ure, now forms part of the
treasures of the British Museum.
At no period in the earth’s history have Reptiles occupied so important
a place as they did in the Jurassic period. Nature seems to have wished
to bring this class of animals to the highest state of development. The
great Reptiles of the Lias are as complicated in their structure as the
Mammals which appeared at a later period. They probably lived, for the
most part, by fishing in shallow creeks and bays defended from heavy
breakers, or in the open sea; but they seem to have sought the shore
from time to time; they crawled along the beach, covered with a soft
skin, perhaps not unlike some of our Cetaceæ. The Ichthyosaurus, from
its form and strength, may have braved the waves of the sea as the
porpoise does now. Its destructiveness and voracity must have been
prodigious, for Dr. Buckland describes a specimen which had between its
ribs, in the place where the stomach might be supposed to have been
placed, the skeleton of a smaller one--a proof that this monster, not
content with preying on its weaker neighbours, was in the habit of
devouring its own kind. In the same waters lived the Plesiosaurus, with
long neck and form more strange than that of the Ichthyosaurus; and
these potentates of the seas were warmed by the same sun and tenanted
the same banks, in the midst of a vegetation not unlike that which the
climate of Africa now produces.
The great Saurians in the Lias of Lyme Regis seem to have suffered a
somewhat sudden death, partly in consequence of a series of small
catastrophes suddenly destroying the animals then existing in particular
spots. “In general the bones are not scattered about, and in a detached
state, as would happen if the dead animal had descended to the bottom of
the sea, to be decomposed, or devoured piecemeal, as, indeed, might also
happen if the creature floated for a time on the surface, one animal
devouring one part, and another carrying off a different portion; on the
contrary, the bones of the skeleton, though frequently compressed, as
must arise from the enormous pressure to which they have so long been
subjected, are tolerably connected, frequently in perfect, or nearly
perfect, order, as if prepared by the anatomist. The skin, moreover, may
sometimes be traced, and the compressed contents of the intestines may
at times be also observed--all tending to show that the animals were
suddenly destroyed, and as suddenly preserved.”[63]
[63] “Geological Manual,” by H. T. De la Beche, 3rd ed., p. 346.
These strange and gigantic Saurians seem almost to disappear during the
succeeding geological periods; for, although they have been discovered
as low down as the Trias in Germany, and as high up as the Chalk in
England, they only appear as stragglers in these epochs; so, too, the
Reptiles, the existing Saurians are, as it were, only the shadowy,
feeble representatives of these powerful races of the ancient world.
Confining ourselves to well-established facts, we shall consider in some
detail the best known of these fossil reptiles--the _Ichthyosaurus_,
_Plesiosaurus_, and _Pterodactyle_.
The extraordinary creature which bears the name of _Ichthyosaurus_ (from
the Greek words Ιχθυς σαυρος, signifying fish-lizard), presents certain
dispositions and organic arrangements which are met with dispersed in
certain classes of animals now living, but they never seem to be again
reunited in any single individual. It possesses, as Cuvier says, the
snout of a dolphin, the head of a lizard, the jaws and teeth of a
crocodile, the vertebræ of a fish, the head and sternum of a lizard, the
paddles like those of a whale, and the trunk and tail of a quadruped.
Bayle appears to have furnished the best idea of the Ichthyosaurus by
describing it as the Whale of the Saurians--the Cetacean of the
primitive seas. It was, in fact, an animal exclusively marine; which, on
shore, would rest motionless like an inert mass. Its whale-like paddles,
and fish-like vertebræ, the length of the tail and other parts of its
structure, prove that its habits were aquatic; as the remains of fishes
and reptiles, and the form of its teeth, show that it was carnivorous.
Like the Whale, also, the Ichthyosaurus breathed atmospheric air; so
that it was under the necessity of coming frequently to the surface of
the water, like that inhabitant of the deep. We can even believe, with
Bayle, that it was provided, like the Whale, with vents or blowers,
through which it ejected, in columns into the air, the water it had
swallowed.
The dimensions of the Ichthyosaurus varied with the species, of which
five are known and described. These are _Ichthyosaurus communis_, _I.
platydon_, _I. intermedius_, _I. tenuirostris_, and _I. Cuvierii_, the
largest being more than thirty feet in length.
[Illustration: Fig. 96.--Ichthyosaurus platydon.]
[Illustration: Fig. 97.--Lower jaw of Ichthyosaurus. (Dr. Buckland.)]
[Illustration: Fig. 98.--Skeleton of Ichthyosaurus.
Containing teeth and bones of Fishes in a coprolitic form. One-fifteenth
natural size.]
The short, thick neck of the Ichthyosaurus supported a capacious head,
and was continued backwards, from behind the eyes, in a column composed
of more than a hundred vertebræ. The animal being adapted, like the
whale, for rapid movement through the water, its vertebræ had none of
the invariable solidity of those of the Lizard or Crocodile, but rather
the structure and lightness of those of Fishes. The section of these
vertebræ presents two hollow cones, connected only by their summits to
the centre of the vertebræ, which would permit of the utmost flexibility
of movement. The ribs extended along the entire length of the vertebral
column, from the head to the pelvis. The bones of the sternum, or that
part of the frame which supported the paddles, present the same
combinations with those of the sternum in the Ornithorhynchus, or
Duck-billed Platypus, of New Holland, an animal which presents the
singular combination of a mammalian furred quadruped having the bill of
a duck and webbed feet; which dived to the bottom of the water in search
of its food, and returned to the surface to breathe the air. In this
phenomenon of living Nature the Creator seems to have repeated, in our
days, the organic arrangements which he had originally provided for the
Ichthyosaurus.
In order that the animal should be able to move with rapidity in the
water, both its anterior and posterior members were converted into fins
or paddles. The anterior fins were half as large again as the posterior.
In some species each paddle was made up of nearly a hundred bones, of
polygonal form, and disposed in series representing the phalanges of the
fingers. This hand, jointed at the arm, bears resemblance, in
osteological construction, to the paddles, without distinct fingers, of
the Porpoise and the Whale. A specimen of the posterior fin of _I.
communis_, discovered at Barrow-on-Soar, in Leicestershire, in 1840, by
Sir Philip Egerton, exhibited on its posterior margin the remains of
cartilaginous rays, which bifurcated as they approached the edge, like
those in the fins of a fish. “It had previously been supposed,” says
Professor Owen, “that the locomotive organs were enveloped, while
living, in a smooth integument, like that of the turtle and porpoise,
which has no other support than is afforded by the bones and ligaments
within; but it now appears that the fin was much larger, expanding far
beyond the osseous frame-work, and deviating widely in its fish-like
rays from the ordinary reptilian type.” The Professor believes that,
besides the fore-paddles, these stiff-necked Saurians were furnished at
the end of the tail with a fin to assist them in turning, not placed
horizontally, as in the whale, but vertically, forming a powerful
instrument of progression and motion. It is obvious that the
Ichthyosaurus was an animal powerfully armed for offence and defence. We
cannot say, with certainty, whether the skin was smooth, like that of
the whale or lizard, or covered with scales, like the great reptiles of
our own age. Nevertheless, as the scales of the Fishes and the cuirass
and horny armour of other Reptiles of the Lias are preserved, and as no
such defensive scales have been found belonging to the Ichthyosaurus, it
is probable that the skin was naked and smooth. The tail, composed of
from eighty to eighty-five vertebræ, was provided with large and long
paddles, arranged vertically as in the Whale.
It is curious to see to what a degree of perfection has been carried, in
our days, the knowledge of the antediluvian animals, their habits, and
their economy. Fig. 98 represents the skeleton of an Ichthyosaurus found
in the Lias of Lyme Regis, which still retains in its abdominal cavity
coprolites, that is to say, the residue of digestion. The soft parts of
the intestinal canal have disappeared, but the _fæces_ themselves are
preserved, and their examination informs us as to the alimentary
regimen of this animal which has perished from the earth many thousands,
perhaps millions, of years. Mary Anning, to whom we owe many of the
discoveries made in the neighbourhood of Lyme Regis, her native place,
had in her collection an enormous coprolite of the Ichthyosaurus. This
coprolite (Fig. 99) contained some bones and scales of Fishes, and of
divers Reptiles, well enough preserved to have their species identified.
It only remains to be added that, among the bones, those of the
Ichthyosaurus were often found, especially those of young individuals.
The presence of the undigested remains of vertebræ and other bones of
animals of its own species in the coprolites of the Ichthyosaurus
proves, as we have already had occasion to remark, that this great
Saurian must have been a most voracious monster, since it habitually
devoured not only fish, but individuals of its own race--the smaller
becoming the prey of the larger. The structure of the jaw of the
Ichthyosaurus leads us to believe that the animal swallowed its prey
without dividing it. Its stomach and intestines must, then, have formed
a sort of pouch of great volume, filling entirely the abdominal cavity,
and corresponding in extent to the great development of the teeth and
jaws.
[Illustration: Fig. 99.--Coprolite, enclosing bones of small
Ichthyosaurus.]
[Illustration: Fig. 100.--Coprolite of Ichthyosaurus.]
The perfection with which its contents have been preserved in the
fossilised coprolites, furnishes indirect proofs that the intestinal
canal of the Ichthyosaurus resembled closely that of the shark and the
dog-fish--fishes essentially voracious and destructive, which have the
intestinal canal spirally convoluted, an arrangement which is exactly
that indicated in some of the coprolites of the Ichthyosaurus, as is
evident from the impressions which the folds of the intestine have left
on the coprolite, of which Fig. 100 is a representation. In the cliffs
near Lyme Regis coprolites are abundant in the Liassic formation, and
have been found disseminated through the shales and limestones along
many miles of that coast.
What an admirable privilege of science, which is able, by an examination
of the simplest parts in the organisation of beings which lived ages
ago, to give to our minds such solid teachings and such true enjoyments!
“When we discover,” says Dr. Buckland, “in the body of an Ichthyosaurus
the food which it has engulfed an instant before its death, when the
intervals between its sides present themselves still filled with the
remains of fishes which it had swallowed some ten thousand years ago, or
a time even twice as great, all these immense intervals vanish, time
disappears, and we find ourselves, so to speak, thrown into immediate
contact with events which took place in epochs immeasurably distant, as
if we occupied ourselves with the affairs of the previous day.”
[Illustration: Fig. 101.--Skull of Plesiosaurus restored. (Conybeare.)
_a_, profile; _b_, seen from above.]
The name of _Plesiosaurus_ (from the Greek words πλησιος, _near_, and
σαυρος, _lizard_) reminds us that this animal, though presenting many
peculiarities of general structure, is allied by its organisation to the
Saurian or Lizard family, and, consequently, to the Ichthyosaurus.
The Plesiosaurus presents, in its organic structure, the most curious
assemblage we have met with among the organic vestiges of the ancient
world. The Plesiosaurus was a marine, air-breathing, carnivorous
reptile, combining the characters of the head of a Lizard, the teeth of
a Crocodile, a neck of excessive length resembling that of a Swan, the
ribs of a Chameleon, a body of moderate size, and a very short tail,
and, finally, four paddles resembling those of a Whale. Let us bestow a
glance upon the remains of this strange animal which the earth has
revealed, and which science has restored to us.
The head of the Plesiosaurus presents a combination of the characters
belonging to the Ichthyosaurus, the Crocodile, and the Lizard. Its
enormously long neck comprises a greater number of vertebræ than the
neck of either the Camel, the Giraffe, or even the Swan, which of all
the feathered race has the longest neck in comparison to the rest of the
body. And it is to be remarked, that, contrary to what obtains in the
Mammals, where the vertebræ of the neck are always seven, the vertebræ
in birds increase in number with the length of the neck.
[Illustration: Fig. 102.--Skeleton of Plesiosaurus dolichodeirus
restored. (Conybeare principally.)]
The body is cylindrical and rounded, like that of the great marine
Turtles. It was, doubtless, naked, _i.e._, not protected with the scales
or carapace with which some authors have invested it; for no traces of
such coverings have been found near any of the skeletons which have been
hitherto discovered. The dorsal vertebræ are attached to each other by
nearly plane surfaces like those of terrestrial quadrupeds, a mode of
arrangement which must have deprived the whole of its vertebral column
of much of its flexibility. Each pair of ribs surrounded the body with a
complete girdle, formed of five pieces, as in the Chameleon and Iguana;
whence, no doubt, as with the Chameleon, great facilities existed for
the contraction and dilatation of the lungs.
[Illustration: Fig. 103.--Sternum and pelvis of Plesiosaurus. Pub.,
pubis; Isch., ischium; Il., ilium.]
The breast, the pelvis, and the bones of the anterior and posterior
extremities furnished an apparatus which permitted the Plesiosaurus,
like the Ichthyosaurus and existing Cetaceans, to sink in the water and
return to the surface at pleasure (Fig. 103). Prof. Owen, in his “Report
on British Reptiles,” characterises them as air-breathing and
cold-blooded animals; the proof that they respired atmospheric air
immediately, being found in the position and structure of the nasal
passages, and the bony mechanism of the thoracic duct and abdominal
cavity. In the first, the size and position of the external nostrils
(Fig. 102), combined with the structure of the paddles, indicate a
striking analogy between the extinct Saurians and the Cetaceans,
offering, as the Professor observes, “a beautiful example of the
adaptation of structure to the peculiar exigencies of species.” While
the evidence that they were cold-blooded animals is found in the
flexible or unanchylosed condition of the osseous pieces of the occiput
and other cranial bones of the lower jaw, and of the vertebral column;
from which the Professor draws the conclusion that the heart was adapted
for transmitting a part only of the blood through the respiratory
organs; the absence of the ball-and-socket articulations of the bones of
the vertebræ, the position of the nostrils near the summit of the head,
the numerous short and flat digital bones, which must have been
enveloped in a simple undivided integumentary sheath, forming in both
fore and hind extremities a paddle closely resembling that of the living
Cetacea. The paddles are larger and more powerful than those of the
Ichthyosaurus, to compensate for the slight assistance the animal
derived from the tail. The latter--shorter, as compared with the length
of the rest of the body, than in the Ichthyosaurus--was more calculated
to act the part of a rudder, in directing the course of the animal
through the water, than as a powerful organ of propulsion.
[Illustration: Fig. 104.--Remains of Plesiosaurus macrocephalus.
One-twelfth natural size.]
Such were the strange combinations of form and structure in the
Plesiosaurus and Ichthyosaurus--genera of animals whose remains have,
after an interment extending to unknown thousands of years, been
revealed to light and submitted to examination; nay, rebuilt, bone by
bone, until we have the complete skeletons before us, and the habits of
the animals described, as if they had been observed in life. Conybeare
thus speaks of the supposed habits of these extinct forms, which he had
built up from scanty materials: “That the Plesiosaurus was aquatic is
evident from the form of its paddles; that it was marine is equally so,
from the remains with which it is universally associated; that it may
have occasionally visited the shore, the resemblance of its extremities
to the turtle may lead us to conjecture; its motion, however, must have
been very awkward on land; its long neck must have impeded its progress
through the water, presenting a striking contrast to the organisation
which so admirably fits the Ichthyosaurus for cutting through the waves.
May it not, therefore, be concluded that it swam on or near the surface,
arching back its long neck like the swan, and occasionally darting it
down at the fish which happened to float within its reach? It may,
perhaps, have lurked in shallow water along the coasts, concealed among
the sea-weeds, and, raising its nostrils to the surface from a
considerable depth, may have found a secure retreat from the assaults of
dangerous enemies, while the length and flexibility of its neck may have
compensated for the want of strength in its jaws, and incapacity for
swift motion through the water, by the suddenness and agility of the
attack they enabled it to make on every animal fitted to become its
prey.”
The Plesiosaurus was first described by the Rev. W. D. Conybeare and Sir
Henry De la Beche, in the “Geological Society’s Transactions” for 1821,
and a restoration of _P. dolichodeirus_, the most common of these
fossils, appeared in the same work for 1824. The first specimen was
discovered, as the Ichthyosaurus had been previously, in the Lias of
Lyme Regis; since then other individuals and species have been found in
the same geological formation in various parts of England, Ireland,
France, and Germany, and with such variations of structure that
Professor Owen has felt himself justified in recording sixteen distinct
species, of which we have represented _P. dolichodeirus_ (Fig. 102), as
restored by Conybeare, and _P. macrocephalus_ (Fig. 104), with its
skeleton, as moulded from the limestone of Lyme Regis, which has been
placed in the Palæontological Gallery of the British Museum.
[Illustration: XV.--Ideal scene of the Lias with Ichthyosaurus and
Plesiosaurus.]
The Plesiosaurus was scarcely so large as the Ichthyosaurus. The
specimen of _I. platydon_ in the British Museum probably belonged to an
animal four-and-twenty feet long, and some are said to indicate thirty
feet, while there are species of Plesiosauri measuring eighteen and
twenty, the largest known specimen of _Plesiosaurus Cramptoni_ found in
the lias of Yorkshire, and now in the Museum of the Royal Society of
Dublin, being twenty-two feet four inches in length. On the opposite
page (PLATE XV.) an attempt is made to represent these grand reptiles of
the Lias in their native element, and as they lived.
Cuvier says of the Plesiosaurus, “that it presents the most monstrous
assemblage of characteristics that has been met with among the races of
the ancient world.” This expression should not be understood in a
literal sense; there are no monsters in Nature; in no living creature
are the laws of organisation ever positively infringed; and it is more
in accordance with the general perfection of creation to see in an
organisation so special, in a structure which differs so notably from
that of the animals of our own days, the simple development of a type,
and sometimes also the introduction of beings, and successive changes in
their structure. We shall see, in examining the curious series of
animals of the ancient world, that the organisation and physiological
functions go on improving unceasingly, and that each of the extinct
genera which preceded the appearance of man, present, for each organ,
modifications which always tend towards greater perfection. The fins of
the fishes of Devonian seas become the paddles of the Ichthyosauri and
of the Plesiosauri; these, in their turn, become the membranous foot of
the Pterodactyle, and, finally, the wing of the bird. Afterwards comes
the articulated fore-foot of the terrestrial mammalia, which, after
attaining remarkable perfection in the hand of the ape, becomes,
finally, the arm and hand of man, an instrument of wonderful delicacy
and power, belonging to an enlightened being gifted with the divine
attribute of reason! Let us, then, dismiss any idea of monstrosity with
regard to these antediluvian animals; let us learn, on the contrary, to
recognise, with admiration, the divine proofs of design which they
display, and in their organisation to see only the handiwork of the
Creator.
Another strange inhabitant of the ancient world, the _Pterodactylus_
(from πτερον, _a wing_, and δακτυλος, _a finger_), discovered in 1828,
made Cuvier pronounce it to be incontestably the most extraordinary of
all the extinct animals which had come under his consideration; and such
as, if we saw them restored to life, would appear most strange and
dissimilar to anything that now exists. In size and general form, and in
the disposition and character of its wings, this fossil genus, according
to Cuvier, somewhat resembled our modern bats and vampyres, but had its
beak elongated like the bill of a woodcock, and armed with teeth like
the snout of a crocodile; its vertebræ, ribs, pelvis, legs, and feet
resembled those of a lizard; its three anterior fingers terminated in
long hooked claws like that on the fore-finger of the bat; and over its
body was a covering, neither composed of feathers as in the bird, nor of
hair as in the bat, but probably a naked skin; in short, it was a
monster resembling nothing that has ever been heard of upon earth,
except the dragons of romance and heraldry. Moreover, it was probably
noctivagous and insectivorous, and in both these points resembled the
bat; but differed from it in having the most important bones in its body
constructed after the manner of those of reptiles.
[Illustration: Fig. 105.--Pterodactylus crassirostris.]
“Thus, like Milton’s fiend, all-qualified for all services and all
elements, the creature was a fit companion for the kindred reptiles that
swarmed in the seas, or crawled on the shores, of a turbulent planet:
“The Fiend,
O’er bog, or steep, through strait, rough, dense, or rare,
With head, hands, wings, or feet, pursues his way,
And sinks, or swims, or wades, or creeps, or flies.
_Paradise Lost_, Book II., line 947.
“With flocks of such-like creatures flying in the air, and shoals of
Ichthyosauri and Plesiosauri swarming in the ocean, and gigantic
Crocodiles and Tortoises crawling on the shores of primæval lakes and
rivers--air, sea, and land must have been strangely tenanted in these
early periods of our infant world.”[64]
[64] Professor Buckland on the Pterodactylus. “Trans. Geol. Soc.,” 2nd
series, vol. iii., p. 217.
[Illustration: Fig. 106.--Pterodactylus brevirostris.]
The strange structure of this animal gave rise to most contradictory
opinions from the earlier naturalists. One supposed it to be a bird,
another a bat, and others a flying reptile. Cuvier was the first to
detect the truth, and to prove, from its organisation, that the animal
was a Saurian. “Behold,” he says, “an animal which in its osteology,
from its teeth to the end of its claws, presents all the characters of
the Saurians; nor can we doubt that their characteristics existed in its
integuments and softer parts, in its scales, its circulation, its
generative organs: it was at the same time provided with the means of
flight; but when stationary it could not have made much use of its
anterior extremities, even if it did not keep them always folded as
birds fold their wings. It might, it is true, use its small anterior
fingers to suspend itself from the branches of trees; but when at rest
it must have been generally on its hind feet, like the birds again, and
like them it must have carried its neck half-erect and curved backwards,
so that its enormous head should not disturb its equilibrium.” This
diversity of opinion need not very much surprise us after all, for, with
the body and tail of an ordinary mammal, it had the form of a bird in
its head and the length of its neck, of the bat in the structure and
proportion of its wings, and of a reptile in the smallness of its head
and in its beak, armed with at least sixty equal sharp-pointed teeth,
differing little in form and size.
Dr. Buckland describes eight distinct species, varying in size from a
snipe to a cormorant. Of these, _P. crassirostris_ (Fig. 105) and _P.
brevirostris_ (Fig. 106), were both discovered in the Lias of
Solenhofen. _P. macronyx_ belongs to the Lias of Lyme Regis.
The Pterodactyle was, then, a reptile provided with wings somewhat
resembling those of Bats, and formed, as in that Mammal, of a membrane
which connected the body with the excessively elongated phalanges of the
fourth finger, which served to expand the membrane that answered the
purposes of a wing. The Pterodactyle of the Liassic period was, as we
have seen, an animal of small size; the largest species in the older
Lias beds did not exceed ten or twelve inches in length, or the size of
a raven, while the later forms found fossil in the Greensand and Wealden
beds must have measured more than sixteen feet between the tips of the
expanded wings. On the other hand, its head was of enormous dimensions
compared with the rest of the body. We cannot admit, therefore, that
this animal could really fly, and, like a bird, beat the air. The
membranous appendage which connected its long finger with its body was
rather a parachute than a wing. It served to moderate the velocity of
its descent when it dropped on its prey from a height. Essentially a
climber, it could only raise itself by climbing up tall trees or rocks,
after the manner of lizards, and throw itself thence to the ground, or
upon the lower branches, by making use of its natural parachute.
The ordinary position of the Pterodactyle was probably upon its two hind
feet, the lower extremities being adapted for standing and moving on the
ground, after the manner of birds. Habitually, perhaps, it perched on
trees; it could creep, or climb along rocks and cliffs, or suspend
itself from trees, with the assistance of its claws and feet, after the
manner of existing Bats. It is even probable, Dr. Buckland thought, that
it had the power of swimming and diving, so common to reptiles, and
possessed by the Vampyre Bat of the island of Bonin. It is believed that
the smaller species lived upon insects, and the larger preyed upon
fishes, upon which it could throw itself like the sea-gull.
The most startling feature in the organisation of this animal is the
strange combination of two powerful wings attached to the body of a
reptile. The imagination of the poets long dwelt on such a combination;
the _Dragon_ was a creation of their fancy, and it played a great part
in fable and in pagan mythology. The Dragon, or flying reptile,
breathing fire and poisoning the air with his fiery breath, had,
according to the fable, disputed with man the possession of the earth.
Gods and demigods claimed, among their most famous exploits, the glory
of having vanquished this powerful and redoubtable monster.
Among the animals of our epoch, only a single reptile is found provided
with wings, or digital appendages analogous to the membranous wings of
the bats, and which can be compared to the Pterodactyle. This is called
the _Dragon_, one of the Draconidæ, a family of Saurians, which has been
described by Daudin, as distinguished by the first six ribs, instead of
hooping round the abdomen, extending in nearly a straight line, and
sustaining a prolongation of skin which forms a sort of wing analogous
to that of the Pterodactyle. Independent of the four feet, this wing
sustains the animal, like a parachute, as it leaps from branch to
branch; but the creature has no power to beat the air with it as birds
do when flying. This reptile lives in the forests of the hottest parts
of Africa, and in some isles of the Indian Ocean, especially in Sumatra
and Java. The only known species is that figured at page 238 (Fig. 107),
which comes from the East Indies.
What a strange population was that which occupied the earth at this
stage of its history, when the waters were filled with creatures so
extraordinary as those whose history we have traced! Plesiosauri and
Ichthyosauri filled the seas, upon the surface of which floated
innumerable Ammonites in light skiffs, some of them as large as a
good-sized cart-wheel, while gigantic Turtles and Crocodiles crawled on
the banks of the rivers and lakes. Only one genus of Mammals had yet
appeared, but no birds; nothing broke the silence of the air, if we
except the breathing of the terrestrial reptiles and the flight of
winged insects.
The earth cooled progressively up to the Jurassic period, the rains lost
their continuity and abundance, and the pressure of the atmosphere
sensibly diminished. All these circumstances favoured the appearance
and the multiplication of innumerable species of animals, whose singular
forms then showed themselves on the earth. We can scarcely imagine the
prodigious quantity of Molluscs and Zoophytes whose remains lie buried
in the Jurassic rocks, forming entire strata of immense thickness and
extent.
[Illustration: Fig. 107.--Draco volans.]
The same circumstances concurred to favour the production of plants. If
the shores and seas of the period received such a terrible aspect from
the formidable animals we have described, the vegetation which covered
the land had also its peculiar character and appearance. Nothing that we
know of in the existing scenery of the globe surpasses the rich
vegetation which decorated the continents of the Jurassic period. A
temperature still of great elevation, a humid atmosphere, and, we have
no reason to doubt, a brilliant sun, promoted the growth of a luxuriant
vegetation, such as some of the tropical islands, with their burning
temperature and maritime climate, can only give us an idea of, while it
recalls some of the Jurassic types of vegetation. The elegant Voltzias
of the Trias had disappeared, but the Horse-tails (_Equiseta_) remained,
whose slender and delicate stems rose erect in the air with their
graceful panicles; the gigantic rushes also remained; and though the
tree-ferns had lost their enormous dimensions of the Carboniferous age,
they still preserved their fine and delicately-cut leaves.
Alongside these vegetable families, which passed upwards from the
preceding age, an entire family--the Cycads (Fig. 72, p. 168)--appear
for the first time. They soon became numerous in genera, such as
Zamites, Pterophyllum (Williamsonia), and Nilssonia. Among the species
which characterise this age, we may cite the following, arranging them
in families:--