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Richard Lydekker.

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rangular bones, which
are believed to have been
arranged in a vertical
position down the middle
of the back, while the tail
was protected by some
formidable spines, as
shown in the greatly
reduced restoration of
the skeleton given on
p. 4. Still more strange
were the somewhat later

horned dinosaurs (Ceratops, etc.), of which two views of the skull and a more
reduced restoration of the skeleton are here given. In these extraordinary
creatures the hinder part of the head was provided with a pair of bony horn-
like projections, which were doubtless ensheathed during life with hollow horns,
like those of oxen; and there w;is also a single horn of variable si/e on the
nose. The skull was further remarkable for the expansion of its hinder extremity
into a fan-like shield overhanging and protecting the vertebrae of the neck. Some
idea of the huge dimensions attained by these dinosaurs will be conveyed by the




UPPER AND SIDE VIEWS OK THE SKULL OF A HORNED DINOSAUR.

a, nostrils ; f, brain ; h, horn ; n, nasal bones ; p, chin-bone ; r, extremity
of upper jaw. After Marsh.



FLYING DRAGONS.



39



statement that an immature skull of one of the species measures upwards of 6 feet,

while fully adult ones must have been considerably larger. The extraordinarily

small size of the brain of these creatures is indicated in the lower figure of

the skull. Externally the bodies of these dinosaurs were protected by granules

and plates of bones, which,

like those of crocodiles, were

probably overlain with horny

shields. It has yet to be

mentioned that in the horned

dinosaurs, as shown in the

figure of the skeleton, the

posterior bar of the pubis has

disappeared, and only the

front branch remains, thus

causing the whole pelvis to

simulate that of the carnivorous group, to which it has no real resemblance.

We have yet to learn the reason why, at the close of the Secondary period,
these mighty dinosaurs, together with the flying dragons which at the same time
tenanted the air, and the fish-lizards and plesiosaurs which peopled the sea, should,
one and all, disappear and that apparently suddenly to make way for mammals
and birds, which henceforth became the lords of creation.




RESTORATION OF THE SKELETON OF A HORNED DINOSAUR.

pd, chin-bone. Other letters as in the figure on p. 4. After Marsh.



FLYING DRAGONS, OR PTERODACTYLES.
Order ORNITHOSAURIA.

At the present day bats and birds are the only Vertebrates endued with the
power of true flight, but during the Secondary period, when the former were
unknown and the latter but poorly represented, the place of both was taken by
the flying dragons, or, as they are called, from the structure of their wings,
Pterodactyles. While agreeing with crocodiles in the essential structure of their
skulls and in their two-headed ribs, these curious reptiles have the other portions
of their skeleton more or less specially modified for the purposes of flight. In the
relatively large size of the brain which is doubtless essential for a flying animal
and general bird-like form of the skull, as well as in the keeled breast-bone and
general form of the collar-bones (although these are not welded together into a
furcula), the pterodactyles present a curious similarity to birds. Misled by these
resemblances, some anatomists have, indeed, been induced to consider that the
two groups are nearly related, although a more mistaken notion never existed.
Such resemblances as do exist between the two groups are due, indeed, to that
parallelism in development to which we have already had occasion to call atten-
tion as existing between totally different groups of animals whose mode of life
is similar.

The most distinctive feature of the pterodactyles is to be found in the
modifications of the bones of the fore-limbs for the purpose of supporting a wing,
which took the form of a membranous expansion of skin analogous to that con-



FLYING DRAGONS.



stituting the wings of bats. This wing was mainly supported by the great
elongation of the bones of the fifth digit or finger of the fore-limb, as shown in
the accompanying figure of the skeleton, and likewise in the restored representation
of one of these reptiles. The membrane thus supported seems to have extended
backwards along the sides of the body to include the upper portions of the legs,
between which it was extended to embrace the base of the tail in those forms in

which the latter appendage was
fully developed. Moreover, in
the long -tailed species, the
extremity of the tail itself was
provided with a racket- shaped
expansion of membrane, which
may have served the purpose of
a rudder in flight. If it be
asked how the presence of such
membranes is known, it may be
answered that in many of the
specimens of these reptiles en-
tombed in the fine-grained litho-
graphic limestones of Bavaria
the actual impressions of these
membranes have been preserved.
The elongated fifth finger of
the wing had no claw at the
extremity, although the three
middle fingers were thus pro-
vided. With regard to the first
finger, or the one corresponding
to the human thumb, this may
have been represented by the

SKELETON OK A PTERODACTYLE. SllUlll Splint - HlvC bone Seen

The creature is lying on its back, with the head bent to the left dependino* from the Wrist in the
side, a indicates the left pubic bone ; the haunch-bone, or ilium. ,_. i i i j. mi i i

being shown on the opposite*,,!,. n g ured skeleton. The Innd-

limbs present no special peculiar-
ities, but, as most of the bones of the skeleton were hollow and permeated by air,
like those of birds, we may infer that the lungs were probably also constructed after
the avian fashion. The vertebra3 of the neck resembled those, of living crocodiles
in having a ball at the hinder end of the body and a cup in front. In general
conformation the skull was remarkably bird-like, the snout being produced into a
beak, which in some cases was provided with teeth, while in others, as shown
in the figure on p. 5, it was toothless, and probably ensheathed during life, with
horn. Bird-like features are likewise shown by the large size of the brain-case.
of which the component bones were fused together, and also by the union of the
extremities of the two branches of the lower jaw.

Pterodactyles flourished during the greater part of the Secondary period, dating
from the epoch of the Lias, and continuing to the close of the one during which the




FLYING DRAGONS. 4I

Chalk was deposited. The}' are represented by several well-marked types, which
my be arranged under three family groups. Of these the most specialised forms
re the toothless pterodactyles, or pteranodonts, from the Cretaceous rocks of North
;rica ; some of these toothless members of the order far exceeded any flying
)ird in point of size; the estimated span of wing in the largest species being
ipvvards of five-and-twenty feet. This group may be distinguished not only by the
)tal absence of teeth, but likewise by the great backward extension of the hinder
itremity of the skull.

In the typical pterodactyles (Pterodactylus. etc.) the jaws were provided with




RESTORATION OP A LONG-TAILED PTERODACTYLE ($ Iiat. size). After Marsh.

3th, which may, however, have been very small in size and few in number,
the skull, as shown in the figure of the skeleton on p. 40, was not produced
jkwardly, and the tail was reduced to a rudiment. The members of this group,
rhich are common in the Oolitic rocks of the Continent, vary in size from the
limensions of a sparrow to those of an eagle. Lastly, we have the long -tailed
pterodactyles (Rliamphorhynchus, etc.), which are likewise of Oolitic and Liassic
re, and are at once distinguished, as shown in the restoration, from the members
}f the preceding group by the fully developed tail. These long-tailed species are
evidently the most generalised members of the order ; and in the retention of the
lil in the generalised group, and its loss in the more specialised one, the reader
not fail to notice an exact parallelism between ordinary bats and the more
lighly-developed fruit-bats.



CHAPTER III.



TORTOISES, TURTLES, AND PLESIOSAURS,
Orders CHELONIA AND SAUROPTERYGIA.

AMONG all existing reptiles the most easily defined are those commonly known as
tortoises and turtles, and technically as Chelonians, since the presence of a more or
less fully developed bony shell investing the body, and containing within it the
upper portions of the limbs, at once separates them from all other members of the
class. Indeed, so utterly strange is the conformation of these extraordinary





UPPER SHELL OF THE CHAIBASSA TERRAPIN, AN1> A FOSSIL SPECIMEN OF THE SAME IN WHICH THE HORNY

SHIELDS ARE WANTING.

reptiles, that if they were met with only in the fossil state they would inevitably
be regarded as among the most marvellous of all creatures. Here however, as
elsewhere, the time-honoured proverb holds good, and our very familiarity from
childhood with the common European land - tortoise undoubtedly tends to
render us inappreciative of the marvellous bodily conformation of this group
of reptiles.

Although the presence of a bony .shell is of itself sufficient to distinguish the



GENERAL CHARACTERISTICS.



43




' group from other living reptiles, it is necessary to add somewhat to this in order
to give a comprehensive definition. As regards the skull, this resembles that of
the crocodiles, in that the quadrate-bone, with which the lower jaw articulates, is
firmly wedged in among the adjacent bones, to which its relations are, however,
somewhat different. Unlike all crocodiles the jaws are, however, entirely devoid
of teeth, and are encased with horn, so as to form a cutting beak, which is invari-
ably short. A further peculiarity in the skull of a tortoise is to be found in the
presence of a greatly developed median spine (sup)
projecting backwards from the hinder region ; exter-
nally to which are a pair of shorter processes. In
other respects, the skull is extremely variable, the
sockets of the eyes being sometimes, as in the figure
on p. 47, surrounded by bone, while in other cases
they are open behind. Sometimes, moreover, the bony
roof behind the eye-socket in the figure on p. 47 may
be prolonged backwards so as to cover the whole
of the region marked par in the annexed figure.
There is an equal amount of variation in regard
to the position of the nostrils, which sometimes open
on the palate close behind the beak, while they may
be situated, as in living crocodiles, close to the hinder
extremity of the skull. A most important feature in
the structure of these animals is to be found in the
circumstance that the ribs have but a single head

, apiece, and that the more anterior ones articulate at

the junction between two of the vertebrae, so that one portion 01 the head is
applied to one vertebra and the other portion to the adjacent vertebra. This

j forms an important distinction from the whole of the orders treated in the
preceding chapter, in all of which the anterior ribs are provided with two heads,
both of which articulate to the sides of one and the same vertebra. Passing on to
the consideration of the bony shell, we find this to consist of an upper portion
or carapace, shown in the figure at the commencement of the chapter, and of an
inferior portion, covering the lower aspect of the body, which is termed the
plastron. When this shell attains its fullest development, the upper and lower
moieties are completely connected together, as shown in the accompanying figure
of the skeleton of a land -tortoise; but in certain groups the two remain more
or less separate, and in some cases the lower shell is but very slightly developed.
Moreover, while the carapace is generally immovably welded to the vertebrae of
the back and the ribs, in the so-called leathery turtle it is separate from both.
In its fullest developed form, the shell consists of a series of bones articulating
witli one another at their edges by finely denticulated sutures, and thus forming
a continuous whole, capable of increasing in sixe by growth at the edges of its
component elements. In the carapace, the bones forming the middle of the back
are formed by expansions growing from the spines of the vertebrae, while the large
lateral plates grow upon the ribs, from which they are inseparable. Within the
cavity thus formed are placed the bones of the shoulder and pelvis, to which are



UPPER VIEW OP THE SKULL OF THE
SOFT-TORTOISE OF THE GANGES.



44



TORTOISES AND TURTLES,




SKELETON OP TORTOISE IN LONGITUDINAL SECTION.



respectively articulated the arm-bone and thigh-bone, so that, as shown in the
figure of the skeleton, these bones actually come within the ribs, instead of being
external to them, as in all other living animals. At the fore and hinder extrem-
ities of the shell are left large apertures, through which are protruded the head
and neck, the fore and hind-limbs, and the tail. A large number of tortoises art-
able to retract both the
head, limbs, and tail
within the margins of
the shell, the apertures
of which are then filled
up ; such portions of the
head and limbs as are
exposed being protected
by horny shields.

With the exception
of the marine leathery
turtles and the fresh-
water soft-tortoises, in
which it is invested merely with a continuous leathery skin, the shell of
Chelonians is covered with a number of horny plates, which, in the adult state at
least, are in contact with one another by their edges. As these horny shields are
very important in determining the different species of tortoises, it is essential to enter
in some detail into their mode of arrangement, and the names by which they are
known. In the carapace of any ordinary tortoise, such as the one represented in
the left-hand figure at the head of the chapter, we shall find that the middle line
of the back, exclusive of the margins, is occupied by a single row of large polygonal
shields, symmetrical in themselves ; these shields, which are marked v in the
accompanying diagram, being known as the vertebrals. On either side of this
median series is another row of shields c, which arc not symmetrical in themselves,
and are termed costals. The extreme margins of the carapace are formed by a
large series of much smaller shields, of which the anterior unpaired one (nu) is
termed the nuchal, and the posterior (ca\ which may be either single or double,
the caudal. Between the nuchal and the caudal are a series, generally eleven in
number on each side, designated marginals (m). These same marginal shields,
being angulated, pass over the edges of the middle portion of the shell, and thus
cover the sides of the middle of the plastron, or lower shell, as shown in the right-
hand figure of the accompanying diagram. The shields of the plastron proper are
generally arranged in pairs, which may be termed, commencing anteriorly, gulor*
(gu), humerals (hit,), pectorals (pc), abdominals (ab), femorals (fe), and anals (n).
In some cases, as will be illustrated in the sequel, the two gulars may, however, be
separated by a single intergular; while, as in the accompanying diagram, there is
frequently an inguinal shield immediately in advance of each notch for the
hind-limbs.

This disposes of the external horny shields; but a few words are necessary
witli regard to the bony elements constituting the shell of a tortoise. On stripping
off these horny shields from the carapace of a tortoise, the underlying solid shell,



GENERAL CHARACTERISTICS.



45



as shown in the right-hand figure at the head of the chapter, will be seen to be
marked by a series of channels corresponding to the borders of these same shields,
it' the shell be not that of a very aged animal, there will be seen in addition a
number of finely jagged sutures, marking the divisions between the component
bones ; and it will be noticed that in their plan of arrangement, although not in
number, size, or shape, these underlying bones correspond very closely with the
overlying horny shields. Thus, in the middle line of the carapace we have a series
of polygonal plates, symmetrical in themselves, and attached to the summits of the
vertebrae, which are known as neurals; these being clearly indicated in the figure
referred to. In front, the series is completed by a large nuchal plate, having no
connection with the backbone, while behind it terminates in one or two pygals,





DIAGRAM OP THE HORNY PLATES ON A SHKLL OP A FRESH-WATER TORTOISE. After Giinther.

are likewise perfectly distinct from the vertebrae. Externally to the neurals
are placed on either side the eight costal plates, so named from being attached to
the ribs ; the inner halves of these plates being alone visible in the shell figured at
the head of the chapter, which belonged to a rather aged animal. Finally, the
edges of the carapace are formed by the 'marginal plates, which, like the horny
shields similarly named, are angulated, and form the lateral borders of the middle

* ' ~ '

portion of the plastron. In the plastron itself, we find its anterior portion formed
by a pair of plates, known as the epiplastrals, corresponding to the collar-bones, or
clavicles, of other Vertebrates ; while between or behind these is a single unpaired
entoplastral element, which may be either dagger-shaped or rhomboidal, and which
represents the interclavicle of less specially modified reptiles. The remainder of
the plastron is formed by three pairs of plates, respectively known as the hyo, hypo,
and xiphiplastrals, of which the latter or hindmost are generally more or less
deeply notched or forked. These three elements appear to correspond to the so-
called abdominal ribs of crocodiles ; and it will thus be evident that Chelonians have



46 TORTOISES AND TURTLES.

no representative of the breast-bone, or sternum, which is so commonly present in
other groups of Vertebrates.

As regards their limbs, the members of this order present a great amount of
variation, some of them, like the laud-tortoises, having the feet adapted for walking,
while in the turtles the entire limbs are modified into paddles for swimming. In
some cases, each of the five toes may be furnished with strong, curved claws, but in
others, like the so ft- tortoises, only three are thus armed. As a general rule, the
number of joints in the toes of the fore-limb, counting from within outwards, is
2, 3, 3, 3, 3, while in the hind-limb they are more generally 2, 3, 3, 3, 2, although
in a few species the number is the same as in the fore-limb. In both limbs the
number of these joints may, however, be reduced, but, except among the soft-
tortoises, they are never augmented. Very generally, the surfaces of the limbs,
especially the anterior ones of the front pair, are protected by horny plates of
variable size, which, among the land-tortoises, may be underlaid by nodules of
bone.

In habits the members of the order display as much diversity as in structure ;
some being carnivorous and others herbivorous, while some are marine, others
fresh- water, and others, again, more or less exclusively inhabitants of dry land.
All, however, are fond of water, and even the most strictly terrestrial species can,
we believe, swim. With the exception of the turtles, the eggs are hard-shelled ;
and these are in all cases deposited on land, the turtles resorting to the shore at
certain seasons for this purpose. As regards distribution, tortoises are especially
characteristic of the warmer parts of the globe, only two species inhabiting Europe
and these confined to the more southern parts of the Continent. The various
groups and families are, however, by no means equally distributed over the
different regions of the globe. The side-necked tortoises, for instance, are now
exclusively confined to the Southern Hemisphere, and in Australia are the only
representatives of the order; whereas the S-necked group attains its greatest
development in the opposite half of the world, although represented in many
countries lying to the south of the Equator. The soft river-tortoises, again, are
confined to the waters of Asia, Africa, and North America, being totally unknown
both in South America and in Australasia, Giant land-tortoises within comparatively
recent times have been confined to what are known as oceanic islands, although
they formerly occurred on most of the large continents ; while the smaller members
of the same genus are far more numerous in South Africa than they are in Asia.
Geologically, the order is a very ancient one, being represented throughout the
whole of the Secondary period, and thus commencing at a date when true crocodiles
are not known to have come into existence.

According to our own views of their mutual relationships, the Chelonians may
be divided into three main groups, or suborders, which may be severally designated
S-necked tortoises (including the turtles), side-necked tortoises, and soft-tortoisea
Some writers would, however, remove from the first group the so-called leathery
turtle, to make it the type of a group equal in value to the whole of the other
three, which are thus collectively brigaded under a common title. Adopting tin;
former arrangement, we commence our survey of the various members of
the order with



LA ND- TOR TOISES



47



THE LAND-TORTOISES AND TERRAPINS,

Family TEVTUDINIDsE.

The land-tortoises, together with tin; greater number of the fresh -water
ises, or terrapins, of .the Northern Hemisphere, as well as their southern
allies, collectively constitute one of several families belonging to the first great
group of the order. From the circumstance that all its
mbers are so constructed as to be able to withdraw
ir heads within the margins of the shell by a bending
the neck in an S-like manner in a vertical plane, the
oip may be conveniently designated S-necked tortoises ;
their scientific designation being Cryptodira. Since, how-

tr, the soft-tortoises likewise retract their heads in a
ilar manner, it is obvious that this character alone will
not suffice to define the group, and it must accordingly be
supplemented by others. Although the degree of ossifi-
cation of the shell is very variable in the group, the
carapace and plastron being in some cases welded into a
complete box, and in other instances separate, yet there
is invariably a complete series of marginal bones, con-
iicfied with the ribs ; the presence of the full series of
marginals, together w r ith the S-like retraction of the neck,
g sufficient to distinguish the group. A peculiarity
which the members of the group differ from those of
e next one, is to be found in the circumstance that the
es of the pelvis remain throughout life unconnected
ith the plastron ; while in the greater number of cases
tin; latter, as shown in the accompanying figure, comprises
only six pairs of horny shields, their being no intergular

between the first pair, or gulars. The skull is characterised by the tympanic
g (t in the accompanying figure) having a notch in its hinder border, and also

by the condyle on its quadrate - bone
fitting into a hollow at the hinder end
of the lower jaw. This S-necked group
includes the marine turtles, and all the
tortoises of the Northern Hemisphere,
with the exception of the soft river-
tortoises, and thus comprises by far the
greater number of the living represent-
atives of the entire order. Although well

PTHE LOWER JA w REMOVED. represented in Africa and South America,

the group is quite unknown in Australia.
The land-tortoises and terrapins of the family Testudinidce have the shell
developed and of a more or less ovoid shape; the plastron being connected
with the carapace either by a straight articulation or by means of sutures, while




THE LEFT HALF OF THE PLAS-
TRON OF THE CHAIBASSA
TERRAPIN.




SIDE VIEW OF THE SKULL OF A LAND-TORTOISE, WITH
THE LOWER JAW REMOVED.






48 TORTOISES AND TURTLES.

it never has an intergular shield in front. The limbs are adapted more or less
completely for walking, and an- never modified into paddles; while the head is
capable of complete retraction within the margins of the shell. A very important
structural feature in the shell is that the nuchal, or unpaired median bone in the
front of the carapace, does not send back processes underlying the marginal bones
of the same ; while in the tail each vertebra has a cup in front of its body or
lower portion, and a ball behind. None of the members of the family are marine
but while some are inhabitants of the land, others are more or less exclusively
dwellers in fresh water. There are, moreover, equally important differences in



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 6 of 62)