REPTILES--MONARCHS OF THE MESOZOIC WORLD
What is a reptile? It is a cold-blooded, air-breathing vertebrate, with
one occipital condyle, complete right and left aortic arches, red blood
and a covering of scales. The classification of the class (Reptilia)
recognizes the existence of many distinct subdivisions, as follows:
_Proreptilia_ (extinct).
_Prosauria_ (extinct, except the tuatara).
_Theromorpha_ (extinct).
_Chelonia_--Turtles; tortoises.
_Dinosauria_ (extinct; dinosaurs).
_Crocodilia_--Crocodiles; alligators.
_Plesiosauria_ (extinct).
_Ichthyosauria_ (extinct; fish lizards).
_Pterosauria_ (extinct; pterodactyls).
_Pythonomorpha_ (extinct; mososaurs, etc.).
_Sauria_--Lizards; snakes.
This surprising diversity of groups, each so widely isolated, as is
implied by separation as subclasses--divisions of almost the highest
rank--shows that the class developed in favorable circumstances that
stimulated enterprise, so to speak, and resulted in rapid variation of
habits, terrestrial, aquatic, arboreal, and aerial, and consequently of
adaptive structure. The fact that most of the subclasses are extinct
also shows us that the story of the Reptilia is mainly a tale of the
departed glory recorded in the archives of the rocks; and we shall
hardly be able to understand living reptiles properly without knowing
something of their prehistoric development into the dominance to which
they rose in the Mesozoic era, which we call Age of Reptiles, and their
subsequent decadence.
The first subclass covers certain most ancient skeletons and parts
of skeletons that naturalists are not yet agreed are true reptiles,
some considering them stegocephalian amphibians. Anyway, they
indicate plainly that it was from that group of Amphibia that the
variety sprang that developed into what, in time, became the distinct
reptilian type. The first distinct product of this departure from
the stegocephalian stock appears in the fossils of a division of
the second subclass, the Prosauria (_pro_, "before"; _saurus_, a
"lizard"), named Rhynchocephalia ("beakheads"), which, although
lizardlike in general form, retain many amphibian characteristics of
structure. Now the amazing and extremely interesting thing about this
is that a representative of this earliest of true reptiles is still
living--probably the premier peer among all vertebrates, reckoned by
length of ancestry. This most primitive of reptiles, illustrating how
hundreds of ancient species known to us only by a few bones must have
appeared and acted in life, is the tuatara of New Zealand, catalogued
in science as _Sphenodon punctatum_.
It has the shape and general appearance of a big lizard, dull in color
and with a granulated rather than scaly hide, and an oddly shaped
head, toothless in the adult, when the jaws become somewhat like a
horny beak. Yet it is not a lizard any more than it is a crocodile or
a turtle, but combines features of all three in its anatomy. Hence it
is what naturalists term a synthetic or generalized race (as is the
case with all very primitive creatures) out of which more and more
specialized groups and species may be, and are, developed, each sorting
out and strengthening some particular characteristic of structure,
continuously modified by adaptations to habits and environment until
a separate type results. The ribs, for example, in the tuatara are
remarkable for the presence of hooklike processes that project backward
from each rib over the next rib behind it; such processes occur
elsewhere only in the crocodiles and the birds. Behind the breastbone
are rodlike bones embedded in the muscles of the belly; they occur
again in the ancient fish lizards and modern crocodiles, and probably
gave rise to the under shield of the turtles. And so on.
The tuatara is verging on extinction. It has nearly disappeared from
the mainland of New Zealand, but is now protected on some small
adjacent islands where it dwells in burrows which it digs and then
shares with petrels. During the greater part of the day the tuataras
sleep; and are fond of lying in the water, being able to remain
submerged for hours without breathing. They feed only upon other
animals.
The third subclass (Theromorpha, "beast-shaped") comprises very ancient
reptiles whose remains lie in the rocks of Permian and Triassic age,
principally in South Africa, and exhibit a skull, and especially teeth,
so much resembling those of carnivorous mammals (for instance, those of
a dog) that at first their true nature was mistaken. These creatures
have excited the most profound interest, not only because they present
so many differences from the Prosauria, but also, and chiefly, because
it is from their ranks that we are able to trace, with no small degree
of certainty, the origin of the Mammalia.
THE SOURCES OF TORTOISE SHELL AND TERRAPIN STEW
The turtles and tortoises are of a very ancient group (Chelonia) and
one very distinct among reptiles, by reason of their armor. What is
known as tortoise shell is the series of horny plates, in some species
of beautiful texture, in others thin and dull, or even leathery
in character, that covers the underlying bones that form the real
protection to the animal's body. In embryo (unhatched) turtles the
skeleton is much like the ordinary four-footed type, with the vertebræ
separate, a full series of ribs, and the limb bones in their proper
places. As growth proceeds, however, changes occur rapidly, but least
in the oceanic "leathery" turtle, in whose skin nodules of bone expand
and join into a mosaic of plates covered with a thick, coriaceous
hide. But this skin remains quite separate from the skeleton beneath,
which fact places this animal in an order Athecæ ("lacking a case"),
quite by itself. All other chelonians are classified in a second order
Thecophora ("case-bearing"), and in them the changes that go on in the
skin to produce the turtle's shell are far more complete.
If you peel off the horny shields on the upper shell, or "carapace,"
you will find beneath them a central, lengthwise row of squarish plates
of bone, on each side of these a row of similar plates, and outside of
these a marginal row of small plates--all knit together at the edges,
the zigzag lines of juncture, or "sutures," being plainly visible.
When we dissect a turtle we find no layer of skin or flesh beneath
these plates, but discover that they lie directly on the bones of
the skeleton and are a part of it. This is what has happened: The
vertebræ have grown together, and the backbone is a tube upon which
the original nodules in the skin have become fixed, and have broadened
into the central line of plates. Those nodules that lay above the
ribs have become fused with them so that no trace of ribs is left,
except where their heads have become fused with the backbone, and they
have broadened into the side rows of plates; and the marginal skin
has become transformed into the marginal plates. Similar alterations
have produced the under shell, or "plastron," replacing the skin; and
adaptive changes have altered the usual relations of the limb bones
to the rest of the external skeleton. The carapace and plastron are
usually connected by a "bridge" of bone.
Into the space within this shell most tortoises may withdraw the head
and tail which, like the feet, are covered with horny scales. The head
has good eyes, and a nose with a lively sense of smell, which the
creature utilizes in selecting its food; but its hearing appears to
be dull. The mouth has no teeth, but the lips are coated with horn,
making a parrotlike beak that can inflict a severe bite. Horny spines
often grow on the legs, or tail, or both, assisting in both defense and
offense.
The chelonians are a very ancient race, and one that has changed
remarkably little since its beginning. The great age accounts for the
very wide distribution of turtles closely related, and also for the
fact that they inhabit land, fresh and salt water; those of the land
being, no doubt, the oldest. All turtles lay eggs, the shell of which
varies, according to kind, from a parchmentlike envelope to a hard,
shining shell; but the process of generation is slow and curiously
complicated.
The respiration of the Chelonia is interesting. The lungs are spongy
masses, attached to the upper shell. As the rigid case does not permit
of their expansion by breathing, the necessary vacuum is made partly
by the neck and limbs, which act like pistons as they are drawn in and
out, the air being swallowed or pumped into the lungs. Most chelonians
may exist for a very long time without breathing, and can stay for
hours or even days under water. No animal, perhaps, is harder to kill;
and all turtles have long lives, the giant turtles of the Galapagos and
their kin living more than 100 years.
The list of Thecophora begins with the suborder Cryptodira, whose
members have the carapace covered with horny shields, and consists
of the family Chelydridæ, composed of our two snapping turtles, the
familiar northern one, and the southern alligator snapper. They inhabit
stagnant pools, especially deep channels in swamps and slow rivers such
as the bayous of the lower Mississippi Valley, and often show only the
tip of the nose as they prowl about close beneath the surface in search
of prey--anything they can seize. They take the hook readily if baited
with fish or flesh, but stout tackle and a strong arm are needed to
land one when full grown; and the act is dangerous to the catcher, for
they are the ugliest brutes in the country, and to be bitten by one
is a very serious experience. Nevertheless, the young are caught for
market in large numbers, for they are excellent food. One curious fact
about them is not generally known, namely, that when lying still, like
a piece of old log covered with mud and moss, they protrude a pair of
wormlike filaments from the tip of the tongue, whose wavering attracts
fishes to their doom. Louis Agassiz says of the great alligator snapper
of the Southern States, which when walking on land carries its body
high on the long legs, much like an alligator:
"They are as ferocious as the wildest beast of prey, but the slowness
of their motions, their inability to repeat the attack immediately,
their awkwardness in attempting to recover their balance when they have
missed their object, their haggard look, and the hideous appearance of
their gaping mouth, constitute at such times a picture as ludicrous
as it is fearful and revolting. Their strength is truly wonderful. I
have seen a large specimen bite off a piece of plank more than an inch
thick.... Fishes, salamanders and young ducks are their ordinary prey.
They lay from twenty to forty or more round eggs, only about the size
of a small walnut, in holes which they dig in sloping banks not far
from the water."
These snapping turtles probably represent well the disposition and
habits of the extinct predatory reptiles; and give us a hint of why the
race succumbed to the more active and intelligent mammals that were
growing up around them toward the close of the Mesozoic.
This brings us to the great family Testudinidæ, which is scattered over
the whole world except Australia, and contains almost all the ordinary
tortoises, mud turtles and terrapins, some of which are entirely
aquatic, others amphibious, others wholly terrestrial. Among the most
typical and widely distributed are those of the genus Chrysemys, to
which "mud turtles" belong. The commonest species in the Eastern
States is the painted turtle _Chrysemys picta_; in the West, _C.
marginata_. These and other species of North and South America are very
pretty when young, the ground color of the upper shields being green,
variegated with yellowish or blackish markings, often in delicate
patterns. They are carnivorous, depend mainly on fish, but eat many
insects and their larvæ. In winter they hibernate in holes in a bank of
their pond.
[Illustration: TERRAPIN
(_Malaclemys palustris_)
(After Babcock. Boston Society of Natural History)]
To the genus Clemmys is credited the "sculptured" wood tortoise, the
keeled plates of whose back are marked with fine concentric grooves
and radiating black lines; and the equally common speckled one, black
with round, orange spots. Both spend long periods wandering in woods
and fields in search of worms and insects. Closely related to them
are the salt-marsh tortoises known as terrapins, which are so much of
a luxury in the eyes of those fond of good dinners that probably the
favorite one, the "diamond back," would be extinct had not protective
measures, and cultivation in captivity, saved the life of the species.
Several other terrapins are to be found in the marshes of the Southern
States, but not in other countries. Another relative is the interesting
little "box tortoise," which is often kept as a pet, and will become
very tame; its highly convex shell is colored black and yellow, or
orange-brown, but no two are alike. The eyes of the male are red, those
of the female yellow. It is naturally enough a "box" tortoise, for,
by means of a flexible joint line across the plastron, the fore and
hinder halves can be brought up to the ends of the carapace, shutting
the whole body inside a tight box that will defy all enemies not strong
enough--as are wolves, bears, and big cats--to tear it to pieces. This
tortoise is exclusively American. It has become, as a species, wholly
terrestrial, so much so that, although it is fond of drinking often,
if it falls into the water it will drown. It thus leads us to the true
land tortoises that fill the remaining genera of this family.
[Illustration: BOX TORTOISE
(_Cistuda carolina_)
(After Babcock. Boston Society of Natural History)]
The typical and most numerous of these belong to the genus Testudo,
with about forty species scattered over all warm or temperate parts of
the world except Australasia. Typically grazers and fruit eaters, they
occasionally vary their diet with worms, snails, and insects. The eggs
are hard-shelled, and the males are usually smaller than their mates.
Most land tortoises hibernate in the ground during the cold half of
the year, or they æstivate during the hot and dry seasons when in the
tropics, but this is not an invariable rule. Several species of these
land tortoises are common and well known in Europe and also in India,
and are often kept as pets. They show considerable intelligence, and
are decidedly fond of listening to music. Our best known American
representative is the "gopher" (_Xerobates polyphemus_) of Florida,
Georgia, and Texas. This turtle is nearly a foot long, with a high,
rounded shell, dull brown in color, and the forefeet covered with
hornlike scales and some spines--an armature for digging. The deserts
along the Mexican border have several local species.
In this family belong the "gigantic" tortoises of the islands east of
Africa and west of South America, now all but extinct, save a few in
captivity in zoölogical gardens. In fact they differ from ordinary land
tortoises mainly in size and in such minor points as distinguish the
various species; some of them, indeed, are not excessive in bulk. The
largest on record is a male of _T. daudini_, of South Aldabra, whose
shell was sixty-seven inches long, and whose living weight was 500
pounds. A fossil species of the late Miocene in India had a shell six
feet long, and then and later tortoises almost as big inhabited both
Europe and North America, and more recently Madagascar. Their survivors
are now restricted to two widely separated regions--the Galapagos
Islands, 600 miles off the coast of Ecuador, and the Mascarenes and
other western islands in the Indian Ocean. The most interesting thing
about this matter is the presence of these tortoises on these widely
scattered islands, and the effects of their isolation. It must be noted
that when discovered by European voyagers no one of these islands,
except the Comoros, was inhabited by men, and none had any large or
harmful beasts of prey.
On these peaceful islands plenty of food, an equable climate, and
absence of enemies, enabled the tortoises in vast numbers to grow to a
size impossible to their relatives on the mainlands. "Scattered over
the many islands they were prevented from interbreeding, and thus it
has come to pass that not only every group of islands, but, in the case
of the Galapagos, almost every island has, or had, its own particular
kind." How did these huge chelonians get to these islands? None like
them is found on any continent at present, although they had a wide
distribution in geological ages. We must conclude that those of the
Madagascar region, at least, are the descendants of tortoises once
populating "Lemuria," that land area which until mid-Tertiary time
occupied the region of the western Indian Ocean, and of which the
existing islands are the remains. A similar theory, for which there
is geological evidence, may account for the survival of the Galapagos
giant tortoises after those of the mainland had died off.
The next family is that of the big sea turtles (Chelonidæ), such as the
green turtle, whose flesh is so highly prized a substance for delicate
soups (but almost all turtle flesh is good eating), the hawksbill and
the loggerhead. They abound in all warm seas, and reach a large size,
the green turtle often having a shell three to four feet long, but
smooth, while that of the hawksbill is covered with horny plates with
high keels and an overlapping arrangement, which are the tortoise shell
of commerce. The green turtle is wholly vegetarian in diet, feeding on
the large seaweeds, while the others are carnivorous, devouring fishes,
mollusks, etc. All three resort in summer to sandy beaches, dig holes,
and bury a great quantity of eggs.
There remains a large group of fresh-water turtles, distinguished,
in addition to other important structural peculiarities, by the fact
that they withdraw the head under the shell by a sidewise bending
of the long neck. They are entirely carnivorous, and occur in all
tropical and some temperate countries, the ferocious "soft shells"
of the Mississippi Valley and northeastward belonging here. A very
curious one is the matamata of Guiana and northern Brazil, the biggest
of its tribe, becoming more than three feet long. It gets its living
by stratagem rather than by activity. The back of its shell is so
roughened by coarse bosses that it looks like the bark on an old log,
and ragged flaps of skin project from head and neck. These are kept in
constant motion, and attract the attention of passing fishes and other
creatures, whose curiosity often takes them too near the treacherous
jaws of the concealed monster.
Our list of turtles ends with the one probably of most importance to
mankind of all the kinds in the world. This is the "arrau" of the
Amazon and Orinoco basins, where it is very abundant, and not only
an essential element in the subsistence of the native Indians, but
of great commercial importance on account of the eggs, which are
periodically collected in enormous quantities, chiefly for their oil.
This oil is eaten, like the eggs themselves, or is used for burning
in lamps, or as an addition to tar. The turtles are likewise eaten by
man and beast. This turtle is large, sometimes three feet long; and it
deposits a great number of soft-shelled eggs in the sand.
[Illustration: HORNED DINOSAUR
(_Monoclonius nasicornus_)
Skeleton restored from bones found in the Red Deer River region,
Canada. (American Museum of Natural History)]
DINOSAURS--ANCESTORS OF BIRDS
No class of the extinct reptiles is so familiar, by name at least, as
is that of the dinosaurs, mainly because of the enormous size of some
of them, and the fact that their prodigious skeletons are exhibited
complete in many museums. No other land animals ever approached some
of them in bulk. A great number of species have been exhumed, yet as
a group these reptiles are only imperfectly known, for the fossils
are not scattered throughout the whole extent of Mesozoic deposits,
but only in two limited periods of that era separated by two or
three millions of years. All of them had short, compact bodies, long
tails, and long legs for a reptile, and instead of crawling they
walked or ran, sometimes upon all fours, more generally on the hind
limbs, like ostriches. They ranged in size from that of a cat to the
prodigious bulk of the diplodocus or the brontosaurus, seventy feet
long and perhaps twenty feet high at the hips, while an East African
species appears to have been even far bigger. Some were herbivorous,
and dwellers mainly in marshes and swamps; others ranged the uplands,
armored for defense against huge predatory kinds, and still others had
horny beaks like birds. It is believed, in fact, that our birds are
descended from the same stock as these creatures, through an early
offshoot.
[Illustration: MONOCLONIUS RESTORATION (DECKERT) IN TYPICAL LANDSCAPE
(American Museum of Natural History)]
CROCODILES AND ALLIGATORS
These repulsive and ferocious reptiles (Crocodilia) are the bulkiest
of the whole class, and most resemble the ancient aquatic dinosaurs,
with which they are undoubtedly allied, although their precise
derivation is undetermined. Their general shape is in conformity with
the reptilian model, rather than indicative of any close relationship
to lizards; indeed their closest living relatives are the tuatara and
the chelonians. They have four legs of nearly equal size in modern
examples, but in some of the older extinct forms of the Lias and
Jurassic strata the hind legs were much longer than the fore pair, and
broadly webbed, while other features indicate a purely marine life;
but it appears plain that the crocodilians originated as land dwellers
whose descendants, early in the history of the group, took to an
amphibious method of life.
The eyes, nostrils, and external ears are situated on the upper surface
of the head, so that breathing, seeing, and hearing are unimpaired in
the water, the upper part of the head being usually raised above the
surface when swimming. The nostrils and ears have valves which are shut
when the animal is under water.
Crocodiles and alligators are mainly carnivorous, feeding on mammals
and waterfowl, for which they lie in wait close to the edge of the
water, sweeping them in by a blow of their tail, but the gavials
feed almost exclusively on fish. All are oviparous, laying oval,
hard-shelled eggs.
The order is represented by a single family, Crocodilidæ, including
six genera scattered through the tropical and subtropical parts of
the globe in the strange fashion that characterizes many of the
ancient groups of which present species are mere relics. Thus the
American genus of alligators has also a species in China; and the Old
World crocodiles are represented by a single, narrowly restricted
species in the region of the Gulf of Mexico. Our common alligator (_A.
mississippiensis_) inhabits the low coastal rivers and swamps from
North Carolina to the Rio Grande, and remains abundant in the steaming
bayous along the lower Mississippi, and in the swamps of Louisiana, but
in Florida has been killed off, not only by the demand for its hide (as
leather), but in a wanton way by tourists and sportsmen, until now its
numbers are greatly reduced. It would have become nearly extinct were
not its prolificness great, each female depositing thirty-five to forty
eggs in the layers of the cone-shaped heap of a nest she makes on the
bank.
Young alligators feed mainly on fish, but the old ones take more and
more to getting birds and beasts for their dinner, stealing on them
quietly as they swim, or when they approach the water to drink. The
prey is dragged down and drowned. In the crocodilian throat the passage
for air from the nostrils reaches much farther back above the mouth
than in other animals, and the entrance of the windpipe may be closed
by pressing together the base of the tongue and the soft palate,
enabling the alligator to drown its prey without drowning itself. In
two particulars our alligator is singular--its fear of man and its
voice. When surprised basking on shore, as it likes to do, it will
rush with awkward haste for the water; and there will get away or out
of sight whenever a man appears. Hence it is safe to bathe in waters
infested by alligators, which will retreat from the feared bather
as far as possible. Nevertheless when an alligator is cornered it
can and will make a very dangerous fight with jaws and tail that are
truly formidable. But it rarely attacks unprovoked, except where a
mother finds you tampering with her nest. As to its noise-making, the
alligator is unique among reptiles in giving voice to a really loud
noise, or bellow, which may sometimes be heard for a mile or more. It
varies according to the size of the reptile from the gentle "mooing" of
a small one to a "thundering and tremendous blast" by a big male.
In the half-submerged morasses of Florida, from Lake Worth southward,
dwells a true crocodile, closely allied to that of the Nile, and first
discovered there by William T. Hornaday in 1875. It differs from the
alligator in the pattern of scales, in the relative length and vertical
flatness of the tail, and especially in having a long, pointed snout
instead of the broad, spade-shaped head of the alligator. Its general
habits present no novelty, but it is more agile and, in captivity, more
vicious than its cousin, while showing a similar dread of man in its
wild home. This crocodile is found from northeastern Mexico south to
the coast of Ecuador, especially in salt marshes.
Central and South America are the habitat of several species of
caymans, which differ from alligators mainly in their teeth and the
fact that protective scales cover the belly; they are blackish in
color, and vary in size and markings, the largest, known on the Amazon
as the black cayman, or "jacare usassu," growing to be twenty feet
long; but the Indians pay little attention to it.
Crocodiles proper (genus Crocodilus) are distinguished by the fact that
some of their foremost teeth fit into a notch of the upper lip, and
are therefore exposed, as is not the case with alligators or gavials.
One species lives in West Africa, another in India, another is wholly
marine in habits (as were some of its extinct progenitors) and ranges
from eastern India and southern China to northern Australia, a fourth
is Australian, and a fifth Central American; but the best known of all
is the so-called Nilotic crocodile of the upper Nile and the rivers
of east central Africa. Formerly it occupied the whole course of the
Nile, and was one of the sacred animals of the priestcraft of ancient
Egypt. In Madagascar it is extraordinarily abundant, and has there the
peculiar habit of digging long, ventilated burrows in the river bank,
in which it lies, and where it stores its prey. Large old specimens
may become fifteen feet in length, and their life is probably very
long, for new teeth grow as fast as the old ones are lost, and when
adult they have no known enemies except one another, but their eggs are
sought for by several kinds of birds, lizards, and so forth, and the
old ones devour many infants.
Crocodiles abound in all the sluggish rivers and estuaries of central
Africa, and are more destructive of human life than even lions or
leopards, and kill much game and many domestic animals. Lying in wait
close to the bank, they make a rush, seize by the nose or leg any
animal as it stoops to drink; or, stealing close to an antelope or goat
standing at the edge of the river, they will, with a sweep of the tail,
knock it into the water, and grasping it with their jaws bear it down
to a horrible death. The crocodile does not at once tear its victim to
pieces, as do the alligators, but pushes it into some hole in the bank
to decompose before being consumed. Major J. Stevenson-Huntington says:
"At Sheshike, on the Zambezi, a paramount chief, who lived some forty
years ago, used to derive great amusement from watching slaves and
criminals being thrown to the crocodiles, his chair being brought
to the river's bank in the cool of the afternoon that he might
enjoy the spectacle in comfort. The crocodiles at this place never
forgot those halcyon days, and, until very recently, it was almost
certain death for anyone to drink at the river, or attempt to draw
water, except within one of the protecting screens of logs which
were erected for the purpose.... On the other hand there are some
large pans in Amatongaland, which, although full of the reptiles,
are said to be quite safe to bathe in, attacks on human beings being
unknown.... Always cunning and suspicious, the crocodile at times
evinces considerable audacity in the pursuit of his prey. Natives are
occasionally knocked off the gunwales of their canoes by a flick from
the tail. I recollect Major Gibbons, standing upright in the stern
of our little aluminum steam launch on the Zambezi, with the tiller
between his feet, nearly losing his balance through an attack of this
kind. I have heard of a native, sleeping on a hot night in the doorway
of a hut close to the river, being attacked and dragged in."
Despite this frequent attack on large prey, fishes are the main
reliance of the African crocodiles for subsistence.
As opposed to this terrifying record from eastern Africa, the
"long-snouted" crocodile of the west coast rivers offers a mild
reputation, since it is content with fish, frogs and water birds as
food, and fears men more than it is feared by them. The natives hunt it
for the sake of its flesh. Crocodile meat is considered good in all
uncivilized parts of the world, but most white men dislike its musky
flavor; the same may be said of the eggs of these reptiles.
The Orient possesses a variety of crocodiles, the best known of which
are the marsh crocodile, a near relative of the African species, and
the gavial, placed in the genus Gavialis, and distinguished by its
long, slender snout and weak teeth. This gavial abounds in the Ganges
and other rivers of northern India and Burma, where it is numerous,
and frequently exceeds twenty feet in length. A second species is
found in the Malayan archipelago. It feeds almost exclusively on fish,
and so rarely harms man or beast that it is regarded as harmless. The
marsh crocodile, or "mugger," is also of great size, and inhabits the
rivers and marshes of India, Ceylon, and the Malayan islands. It is
a fish eater and an arrant coward, feared by no one under ordinary
conditions. It was, perhaps, originally, as a matter of gratitude for
this harmlessness, that the custom arose among the Hindus of venerating
this reptile. In some places, as notably near Karachi, large numbers of
muggers are kept captive in ponds, and attended by priests and devotees
who guard and feed them.
A third species is the formidable "estuarine" crocodile, which
frequents the tidal portions of rivers from the Bay of Bengal to China
and Australia. It exceeds all of its race in stature, usually exceeding
twenty feet long, and one old specimen on record was thirty-three feet
from tip to tip. It is held in great fear by fishermen, for in many
cases it develops man-eater proclivities, and has all the ferocity
and resourcefulness of its Nilotic cousin. The salt-water habitat
of this species recalls the fact that among the many kinds of fossil
crocodilians known, from the Lias onward, one was a purely marine form.
The crocodiles are followed in the classification of the reptiles by
several extinct groups, known only as fossils of the Mesozoic Age.
The first of these is the subclass Plesiosauria, containing a series
of predatory creatures characterized by very long necks, short tails,
and feet that in the older forms indicate a terrestrial existence, but
later exhibit a progressive change to paddles, showing that finally
the plesiosaurs were wholly aquatic. This was accompanied by a steady
increase in size, until finally a length of at least forty-five feet
was reached--chiefly by extension of the neck--in the elasmosaurus of
the Cretaceous rocks of Kansas.
Another subclass, Ichthyosauria, restricted to the Mesozoic Age, were
large, swimming, marine "fish lizards" with a somewhat whalelike form,
the front limbs transformed into paddles, and the snout in the form of
a long bill filled with sharp teeth. They lived on fishes, cuttlefish,
mollusks, etc., and had the general habits of sharks. They died out
early in the Cretaceous epoch, and left no descendants.
A third extinct subclass is that of the pterodactyls, or "flying
dragons" (Pterosauria), which possessed the air throughout the Mesozoic
Age, and filled the place of birds in the fauna of that period,
although they had no relationship to the real birds that came later.
Some were no larger than sparrows, but later ones spread their leathery
wings twenty feet or more. The origin and real affinities of these
winged reptiles are unknown and they left no descendants.
We find in the Cretaceous formations skeletons of very long, slender
marine reptiles (Pythonomorpha) with a lizardlike head and all four
limbs in the form of paddles, of which the mososaurs are the best
known. These were the latest of the Mesozoic reptiles; and about the
time of their disappearance we begin to find the earliest fossil
suggestions of the subclass Sauria which contains our modern orders
Lacertilia, the lizards, and Ophidia, the serpents. Neither of these
owe their ancestry to any of the fossil groups just mentioned, in spite
of superficial resemblances, but "their origin has probably to be
looked for among the Prosauria, of which Sphenodon (the tuatara, see
page 183) is the only surviving member." They are also very distinct
from crocodiles in structure.
[Illustration: MESOZOIC FLYING REPTILE (PTERODACTYL)
(Restoration, after Owen)]
LIZARDS AND CHAMELEONS--TURNCOATS OF THE WOODS
Lizards (Lacertilia) are creatures of hot climates, and especially of
deserts, and they exhibit an almost endless variety of shape, size,
structure, and adaptations to their surroundings and a mode of life
that is primarily dictated by their food. The majority are terrestrial,
but some species are semiaquatic. There are climbing, swiftly running,
and even flying forms, while others lead a subterranean life like
earthworms. Most of them subsist on animal food, varying from tiny
insects and worms to birds and mammals, while others live upon a
vegetable diet.
Lizards, like snakes, have a scaly skin covered with a thin, horny
pellicle which is shed from time to time, flaking off in pieces except
in the wormlike species, where it is sloughed whole as by snakes. In
most lizards the scales are well developed, and "shingle" the back and
sides of the body, but in some they are like little tubercles, giving a
granular appearance--a good example of which is the "Gila monster" of
Arizona. Lizards are, as a rule, adaptively colored according to their
habitat, so that browns and grays prevail in the sand-running species
or those, like the monitors and iguanas, that are mostly aquatic; but
brilliant hues in varied, even fantastic, patterns adorn many of the
small, agile, tropical kinds, whose safety lies in their swiftness
of movement and cleverness in hiding. This is supplemented in most
species by the capability of changing color, a faculty that is most
serviceable in the chameleons, by rendering them more or less invisible
to the hawks and other animals that try to catch and eat them. Some of
the more sluggish, earth-dwelling kinds are further protected by many
spines sprouting from the skin, as is familiar in our western "horned
toad," and in the fearsome-looking "moloch" of Australia; and the
iguanas are provided with an erectile spiny crest along the ridge of
their backs, most notable in the basilisks.
A strange characteristic of most lizards with slender tails is the
power to part with them at a moment's notice. If an enemy seizes this
appendage, which often is held temptingly aloft, it breaks off and its
owner escapes before the would-be captor has had time to recover from
his surprise. Within a short time a new tail is developed, but it is
never so perfect as the original organ.
Most lizards lay eggs, few in number, and with shells hard in some
families, parchmentlike in others, that are hidden in a hole in a dead
stump or some similar place of concealment, and are left to be hatched
by the warmth of the sun. Many lizards retain their eggs until nearly
ready to hatch, and so are practically viviparous. The embryos have an
"egg tooth," as do turtles and snakes.
The Lacertilia are naturally divisible into three sections, namely,
geckos, typical lizards, and chameleons.
The geckos are a large and ancient family represented in all
tropical countries, and some species are common along both shores
of the Mediterranean, but none reach the United States. They are
small, plump, flat-headed, and mostly somber in color, but this is
changeable; the skin has a granular surface, but regular scales cover
the desert-dwelling species. One peculiarity of the group is the
adaptation of the foot to the habit of climbing about rocks and trees.
The undersurface of the toes has a series of plates, which serve as
adhesive pads wherewith the animal is enabled to climb not only trees
and the smooth rocks, but a windowpane or to run along the ceiling with
the ease of a fly. Another peculiarity is the fact that the eyeball is
covered by a "watch glass" of transparent skin, under which the little
animal rolls its eyes and stares at you with vigilant interest. Geckos
are nocturnal in habit, and as evening approaches come out from their
retreats and become active in hunting for insects, and in avoiding the
other lizards, snakes, and so forth, that would like to seize and eat
them; and it is then that are heard their low, two-syllabled, clucking
calls that give them the name "gec-ko." These funny little lizards
are utterly harmless, come into houses, and are easily tamed, yet are
regarded in many countries with superstitious dread and that foolish
fear of poison that is attached to most small lizards and newts. In the
Orient several strangely modified forms exist.
The lizards proper (Lacertæ) number several hundred species classified
in eighteen families, and differ vastly in size, shape, food, and place
and manner of life. Some, like the degraded slowworms, are limbless,
scaleless and in their serpentine form and underground life resemble
worms more than anything else. Others, such as the "flying dragons" of
Malayan forests, have developed great winglike expansions of the skin
on the sides, folded close to the body as they climb about the trees,
but capable of being spread as supports when they wish to take a long
gliding leap to some distant perch; and an Australian species has
similar skin expansions that can be raised into a broad ruff around the
neck that gives the little animal a terrifying aspect. The many kinds
that live in deserts have the dull hue of the ground, or may bristle
with spines, of which the squat "horned toad" of California is an
excellent example; while those that scamper about the trees and rocks
of the equatorial region are often brilliantly striped or spotted in
reds, greens and blues. Many are pugnacious and able to bite severely,
but the only one whose bite is poisonous is the heloderma of the
Mexican border. This is a fat, sluggish, black and yellow creature,
about a foot in length, that inhabits the hot desert sands. Fortunately
it is slow to anger, but when it does bite there flows into the wound
a poison which has the same effect as the venom of the rattlesnake,
although less copious and virulent. Severe illness, and in a few cases
death, have resulted from the bite of this ugly creature, which is more
commonly known as the "Gila monster," because it is prevalent in the
valley of the Gila River in southern Arizona.
As the great family Agamidæ is confined to the Old World, so the
Iguanidæ belongs to America, where several species are numerous in the
tropics, and reach a size of three to five feet, much of which is tail.
They live in trees, feed on vegetation, and haunt the banks of rivers
into which they jump on the slightest alarm. One traveler relates that
along the Mosquito Coast of Nicaragua, when a person is going in a
canoe up some of the narrow, unfrequented creeks, he encounters quite
a shower of iguanas, and runs some risk of getting his neck broken,
for a big iguana will weigh twenty-five pounds or more. Their flesh,
resembling that of chicken, is a favorite article of food and iguanas
are constantly brought to rural markets. The family contains about 300
species. Among them is the common little "chameleon" (Anolis) of our
Gulf States, so often sold to tourists as a curiosity, and brought
north to die of cold and neglect. It is golden green on the upper
surface, and white on the under, and the throat, when inflated, glows
with vermilion; it is a harmless, active little tree dweller, and will
change its colors to suit its surroundings with astonishing rapidity.
In another genus (Sceloporus) is placed the blue-tailed, variable,
"fence lizard," or "swift," which is known throughout the eastern
United States; but the common small lizards of the Pacific slope belong
to Gherronotus and other genera.
The largest lizards of all belong to the two families Varanidæ, the
"monitors" of Africa and eastward to Australia, and Teidæ, the "tejus"
of Central and South America. They are singularly alike in appearance
and habits--long-tailed, slender, smooth-skinned, carnivorous
creatures, living in all sorts of places, varying with the numerous
species, and both hated and utilized by the natives of the various
countries they inhabit. Some monitors are more than seven feet long.
The American tejus, such as the big "teguexin" of Brazil, frequent
forests and plantations, where their strength and speed enable them to
catch all kinds of animals, from insects to worms, frogs, snakes, mice,
and birds. "They take chickens and eggs from the farms, and they are
frequently hunted down by dogs for the sake of their flesh, which is
considered good to eat. They defend themselves with lashing strokes of
their long tail and with their powerful jaws."
The chameleons differ so much from other lizards that they have
been placed by some systemists in a different suborder. The chief
differences are three. First, the feet, terminating rather long legs,
have the fingers and toes so arranged that two digits oppose three
as do our thumbs the palm of the hand, and the animal can grasp a
branch just as we would, giving so firm a grip that chameleons are
exceedingly agile climbers, and may take as many odd attitudes among
the branches as would a monkey. Second, the eyes are very large, but
the eyelids have grown together over them, leaving only a small hole
out of which to look. The right and left eye roll about incessantly,
and independently, giving a most comical squinting effect--but no
lizard sees with both eyes at once! Third, the tongue has reached an
extraordinary development. When the mouth is shut it is withdrawn into
a tubular sheath at the back of the mouth; but when a fly is seen and
wanted it is shot out like a released spring, seizes the fly in the
flaps at its club-shaped extremity, and is quickly withdrawn. This
tongue may be thrust out to a distance equal to the length of the body,
less the long, tapering, prehensile tail, which is another important
part of the equipment of these active tree dwellers. The skin is not
scaly, but granular in appearance; and the skull is prolonged behind
into a pointed helmetlike form that is distinctive of the group.
Chameleons are most celebrated, however, for their remarkable power
of changing their color, but this is by no means always, or perhaps
often in direct response to the hue of their immediate surroundings.
Dr. Hans Gadow has made an extensive study of his captive specimens of
the common chameleon of the Mediterranean region, and confesses himself
baffled in the attempt to learn an explanation of the influences,
external or mental, that causes the alterations of hue. One judges
from his observations that they are mainly the expression of fleeting
emotions--but who can read the emotions of a lizard?
But if we do not know the _why_, the _how_ of these fluctuations of
color is well understood, and is briefly stated by Prof. Pycraft:
"The horny outermost layer of the skin is colorless; in the layer
beneath this are embedded iridescent cells with striated surfaces.
Below this, in the deepest layer of the skin, _cutis_, are a large
number of cells filled with refractive granules, chiefly guanin
crystals. These cause white color by diffuse reflection of direct
light. Nearer the surface are cells filled with oil drops, and these
give a yellow color. In the granular mass are embedded numerous
color-bearing granular sacs or chromatophores, containing for the most
part blackish brown or reddish pigment. The branches of these sacs
being contractile, the contained granules of color are drawn away
from or toward the surface of the skin, and thus, combining with the
stationary color, effect a corresponding change in the coloration of
the animal."
The chameleons are an African family, but a few of the fifty or so
species belong also to the western coast of India and Ceylon, and one
is a resident of southern Spain. They vary in size from that of a mouse
to a species in Madagascar two feet long.
The lizards and snakes are the most recent developments of the
reptilian line of vertebrate evolution. No undoubted lizard remains
have been discovered antedating the end of the Cretaceous epoch; and no
fossil evidences of snakes are much older than the mid-Tertiary, yet
these are surprisingly similar to existing forms. The affinities of
both groups seem to be with Pythonomorpha.