Mosasaurs, and hundreds--aye, thousands--of specimens have been taken
from the chalk bluffs of that region, some of them in such a fine state
of preservation that we are not only well acquainted with their internal
structure, but with their outward appearance as well. They were
essentially swimming lizards--great, overgrown, and distant relatives of
the Monitors of Africa and Asia, especially adapted to a roving,
predatory life by their powerful tails and paddle-shaped feet. Their
cup-and-ball vertebrae indicate great flexibility of the body, their
sharp teeth denote ability to capture slippery prey, and the structure
of the lower jaw shows that they probably ate in a hurry and swallowed
their food entire, or bolted it in great chunks. The jaws of all
reptiles are made up of a number of pieces, but these are usually so
spliced together that each half of the jaw is one inflexible, or nearly
inflexible, mass of bone. In snakes, which swallow their prey entire,
the difficulty of swallowing animals greater in diameter than themselves
is surmounted by having the two halves of the lower jaw loosely joined
at the free ends, so that these may spread wide apart and thus increase
the gape of the mouth. This is also helped by the manner in which the
jaw is joined to the head. The pelican solves the problem by the length
of his mandibles, this allowing so much spring that when open they bow
apart to form a nice little landing net. In the Mosasaurs, as in the
cormorants, among birds, there is a sort of joint in each half of the
lower jaw which permits it to bow outward when opened, and this, aided
by the articulation of the jaw with the cranium, adds greatly to the
swallowing capacity. Thus in nature the same end is attained by very
different methods. To borrow a suggestion from Professor Cope, if the
reader will extend his arms at full length, the palms touching, and then
bend his elbows outward he will get a very good idea of the action of a
Mosasaur's jaw. The western sea was a lively place in the day of the
great Mosasaurs, for with them swam the king of turtles, Archelon, as
Mr. Wieland has fitly named him, a creature a dozen feet or more in
length, with a head a full yard long, while in the shallows prowled
great fishes with massive jaws and teeth like spikes.
[Illustration: Fig. 10.--Jaw of a Mosasaur, Showing the Joint that
Increased the Swallowing Capacity of that Reptile.]
There, too, was the great, toothed diver, Hesperornis (see page 83),
while over the waters flew pterodactyls, with a spread of wing of twenty
feet, largest of all flying creatures; and, not improbably--nay, very
probably--fish-eaters, too; and when each and all of these were seeking
their dinners, there were troublous times for the small fry in that old
Kansan sea.
And then there came a change; to the south, to the west, to the north,
the land was imperceptibly but surely rising, perhaps only an inch or
two in a century, but still rising, until "The Ocean in which flourished
this abundant and vigorous life was at last completely inclosed on the
west by elevations of sea-bottom, so that it only communicated with the
Atlantic and Pacific at the Gulf of Mexico and the Arctic Sea."
The continued elevation of both eastern and western shores contracted
its area, and when ridges of the sea-bottom reached the surface, forming
long, low bars, parts of the water-area were included, and connection
with salt-water prevented. Thus were the living beings imprisoned and
subjected to many new risks to life. The stronger could more readily
capture the weaker, while the fishes would gradually perish through the
constant freshening of the water. With the death of any considerable
class, the balance of food-supply would be lost, and many large species
would disappear from the scene. The most omnivorous and enduring would
longest resist the approach of starvation, but would finally yield to
inexorable fate--the last one caught by the shifting bottom among
shallow pools, from which his exhausted energies could not extricate
him.[5]
[5] _Cope: "The Vertebrata of the Cretaceous Formations of the West," p.
50, being the "Report of the United States Geological Survey of the
Territories," Vol. II._
Like the "Fossil man" the sea-serpent flourishes perennially in the
newspapers and, despite the fact that he is now mainly regarded as a
joke, there have been many attempts to habilitate this mythical monster
and place him on a foundation of firm fact. The most earnest of these
was that of M. Oudemans, who expressed his belief in the existence of
some rare and huge seal-like creature whose occasional appearance in
southern waters gave rise to the best authenticated reports of the
sea-serpent. Among other possibilities it has been suggested that some
animal believed to be extinct had really lived over to the present day.
Now there are a few waifs, spared from the wrecks of ancient faunas,
stranded on the shores of the present, such as the Australian Ceratodus
and the Gar Pikes of North America, and these and all other creatures
that could be mustered in were used as proofs to sustain this theory.
If, it was said, these animals have been spared, why not others? If a
fish of such ancient lineage as the Gar Pike is so common as to be a
nuisance, why may there not be a few Plesiosaurs or a Mosasaur somewhere
in the depths of the ocean? The argument was a good one, the more that
we may "suppose" almost anything, but it must be said that no trace of
any of these creatures has so far been found outside of the strata in
which they have long been known to occur, and all the probabilities are
opposed to this theory. Still, if some of these creatures _had_ been
spared, they might well have passed for sea-serpents, even though
Zeuglodon, the one most like a serpent in form, was the one most
remotely related to snakes.
Zeuglodon, the yoke-tooth, so named from the shape of its great cutting
teeth, was indeed a strange animal, and if we wonder at the Greenland
Whale, whose head is one-third its total length, we may equally wonder
at Zeuglodon, with four feet of head, ten feet of body, and forty feet
of tail. No one, seeing the bones of the trunk and tail for the first
time, would suspect that they belonged to the same animal, for while the
vertebrae of the body are of moderate size, those of the tail are, for
the bulk of creature, the longest known, measuring from fifteen to
eighteen inches in length, and weighing in a fossil condition fifty to
sixty pounds. In life, the animal was from fifty to seventy feet in
length, and not more than six or eight feet through the deepest part of
the body, while the tail was much less; the head was small and pointed,
the jaws well armed with grasping and cutting teeth, and just back of
the head was a pair of short paddles, not unlike those of a fur seal. It
is curious to speculate on the habits of a creature in which the tail
so obviously wagged the dog and whose articulations all point to great
freedom of movement up and down. This may mean that it was an active
diver, descending to great depths to prey upon squid, as the Sperm-Whale
does to-day, while it seems quite certain that it must have reared at
least a third of its great length out of water to take a comprehensive
view of its surroundings. And if size is any indication of power, the
great tail, which obviously ended in flukes like those of a whale, must
have been capable of propelling the beast at a speed of twenty or thirty
miles an hour. Something of the kind must have been needed in order that
the small head might provide food enough for the great tail, and it has
been suggested that inability to do this was the reason why Zeuglodon
became extinct. On the other hand, it has been ingeniously argued that
the huge tail served to store up fat when food was plenty, which was
drawn upon when food became scarce. The fur seals do something similar
to this, for the males come on shore in May rolling in blubber, and
depart in September lean and hungry after a three months' fast.
Zeuglodons must have been very numerous in the old Gulf of Mexico, for
bones are found abundantly through portions of our Southern States; it
was also an inhabitant of the old seas of southern Europe, but, as we
shall see, it gave place to the great fossil shark, and this in turn
passed out of existence. Still, common though its bones may be, stories
of their use for making stone walls--and these stories are still in
circulation--resolve themselves on close scrutiny into the occasional
use of a big vertebra to support the corner of a corn-crib.
The scientific name of Zeuglodon is _Basilosaurus cetoides_, the
whale-like king lizard--the first of these names, _Basilosaurus_, having
been given to it by the original describer, Dr. Harlan, who supposed the
animal to have been a reptile. Now it is a primary rule of nomenclature
that the first name given to an animal must stick and may not be
changed, even by the act of a zooelogical congress, so Zeuglodon must, so
far as its name is concerned, masquerade as a reptile for the rest of
its paleontological life. This, however, really matters very little,
because scientific names are simply verbal handles by which we may grasp
animals to describe them, and Dr. Le Conte, to show how little there may
be in a name, called a beetle Gyascutus. Owen's name of Zeuglodon,
although not tenable as a scientific name, is too good to be wasted, and
being readily remembered and easily pronounced may be used as a popular
name.
[Illustration: Fig. 11.--Koch's Hydrarchus, Composed of Portions of the
Skeleton of Several Zeuglodons.]
One might think that a creature sixty or seventy feet long was amply
long enough, but Dr. Albert Koch thought otherwise, and did with
Zeuglodon as, later on, he did with the Mastodon, combining the vertebrae
of several individuals until he had a monster 114 feet long! This he
exhibited in Europe under the name of Hydrarchus, or water king, finally
disposing of the composite creature to the Museum of Dresden, where it
was promptly reduced to its proper dimensions. The natural make-up of
Zeuglodon is sufficiently composite without any aid from man, for the
head and paddles are not unlike those of a seal, the ribs are like those
of a manatee, and the shoulder blades are precisely like those of a
whale, while the vertebrae are different from those of any other animal,
even its own cousin and lesser contemporary Dorudon. There were also
tiny hind legs tucked away beneath skin, but these, as well as many
other parts of the animal's structure were unknown, until Mr. Charles
Schuchert collected a series of specimens for the National Museum, from
which it was possible to restore the entire skeleton. Owing to a rather
curious circumstance the first attempt at a restoration was at fault;
among the bones originally obtained by Mr. Schuchert there were none
from the last half of the tail, an old gully having cut off the hinder
portion of the backbone and destroyed the vertebrae. Not far away,
however, was a big lump of stone containing several vertebrae of just the
right size, and these were used as models to complete the papier-mache
skeleton shown at Atlanta, in 1894. But a year after Mr. Schuchert
collected a series of vertebrae, beginning with the tip of the tail, and
these showed conclusively that the first lot of tail vertebrae belonged
to a creature still undescribed and one probably more like a whale than
Zeuglodon himself, whose exact relationships are a little uncertain, as
may be imagined from what was said of its structure. Mixed with the
bones of Zeuglodon was the shell of a turtle, nearly three feet long,
and part of the backbone of a great water-snake that must have been
twenty-five feet long, both previously quite unknown. One more curious
thing about Zeuglodon bones remains to be told, and then we are done
with him; ordinarily a fossil bone will break indifferently in any
direction, but the bones of Zeuglodon are built, like an onion, of
concentric layers, and these have a great tendency to peel off during
the preparation of a specimen.
* * * * *
And now, as the wheels of time and change rolled slowly on, sharks again
came uppermost, and the warmer Eocene and Miocene oceans appear to have
fairly teemed with these sea wolves. There were small sharks with
slender teeth for catching little fishes, there were larger sharks with
saw-like teeth for cutting slices out of larger fishes, and there were
sharks that might almost have swallowed the biggest fish of to-day
whole, sharks of a size the waters had never before contained, and
fortunately do not contain now. We know these monsters mostly by their
teeth, for their skeletons were cartilaginous, and this absence of their
remains is probably the reason why these creatures are passed by while
the adjectives huge, immense, enormous are lavished on the Mosasaurs and
Plesiosaurs--animals that the great-toothed shark, _Carcharodon
megalodon_, might well have eaten at a meal. For the gaping jaws of one
of these sharks, with its hundreds of gleaming teeth must, at a moderate
estimate, have measured not less than six feet across.
The great White Shark, the man-eater, so often found in story books, so
rarely met with in real life, attains a length of thirty feet, and a man
just makes him a good, satisfactory lunch. Now a tooth of this shark is
an inch and a quarter long, while a tooth of the huge _Megalodon_ is
commonly three, often four, and not infrequently five inches long.
Applying the rule of three to such a tooth as this would give a shark
120 feet long, bigger than most whales, to whom a man would be but a
mouthful, just enough to whet his sharkship's appetite. Even granting
that the rule of three unduly magnifies the dimensions of the brute, and
making an ample reduction, there would still remain a fish between
seventy-five and one hundred feet long, quite large enough to satisfy
the most ambitious of _tuna_ fishers, and to have made bathing in the
Miocene ocean unpopular. Contemporary with the great-toothed shark was
another and closely related species that originated with him in Eocene
times, and these two may possibly have had something to do with the
extinction of Zeuglodon. This species is distinguished by having on
either side of the base of the great triangular cutting teeth a little
projection or cusp, like the "ear" on a jar, so that this species has
been named _auriculatus_, or eared. The edges of the teeth are also more
saw-like than in those of its greater relative, and as the species must
have attained a length of fifty or sixty feet it may, with its better
armature, have been quite as formidable. And, as perhaps the readers of
these pages may know, the supply of teeth never ran short. Back of each
tooth, one behind another arranged in serried ranks, lay a reserve of
six or seven smaller, but growing teeth, and whenever a tooth of the
front row was lost, the tooth immediately behind it took its place, and
like a well-trained soldier kept the front line unbroken. Thus the teeth
of sharks are continually developing at the back, and all the teeth are
steadily pushing forward, a very simple mechanical arrangement causing
the teeth to lie flat until they reach the front of the jaw and come
into use.
Once fairly started in life, these huge sharks spread themselves
throughout the warm seas of the world, for there was none might stand
before them and say nay. They swarmed along our southern coast, from
Maryland to Texas; they swarmed everywhere that the water was
sufficiently warm, for their teeth occur in Tertiary strata in many
parts of the world, and the deep-sea dredges of the Challenger and
Albatross have brought up their teeth by scores. And then--they
perished, perished as utterly as did the hosts of Sennacherib. Why? We
do not know. Did they devour everything large enough to be eaten
throughout their habitat, and then fall to eating one another? Again, we
do not know. But perish they did, while the smaller white shark, which
came into being at the same time, still lives, as if to emphasize the
fact that it is best not to overdo things, and that in the long run the
victory is not _always_ to the largest.
_REFERENCES_
_The finest Mosasaur skeleton ever discovered, an almost complete
skeleton of Tylosaurus dyspelor, 29 feet in length, may be seen at the
head of the staircase leading to the Hall of Paleontology, in the
American Museum of Natural History, New York. Another good specimen may
be seen in the Yale University Museum, which probably has the largest
collection of Mosasaurs in existence. Another fine collection is in the
Museum of the State University of Kansas, at Lawrence._
_The best Zeuglodon, the first to show the vestigial hind legs and to
make clear other portions of the structure, is in the United States
National Museum._
_The great sharks are known in this country by their teeth only, and, as
these are common in the phosphate beds, specimens may be seen in
almost any collection. In the United States National Museum, the jaws of
a twelve-foot blue shark are shown for comparison. The largest tooth in
that collection is 5-3/4 inches high and 5 inches across the base. It
takes five teeth of the blue shark to fill the same number of inches._
_The Mosasaurs are described in detail by Professor S. W. Williston, in
Vol. IV. of the "University Geological Survey of Kansas." There is a
technical--and, consequently, uninteresting--account of Zeuglodon in
Vol. XXIII. of the "Proceedings of the United States National Museum,"
page 327._
[Illustration: Fig. 12.--A Tooth of Zeuglodon, one of the "Yoke Teeth,"
from which it derives the name.]
V
BIRDS OF OLD
"_With head, hands, wings, or feet, pursues his way,
And swims, or sinks, or wades, or creeps, or flies._"
When we come to discuss the topic of the earliest bird--not the one in
the proverb--our choice of subjects is indeed limited, being restricted
to the famous and oft-described Archaeopteryx from the quarries of
Solenhofen, which at present forms the starting-point in the history of
the feathered race. Bird-like, or at least feathered, creatures, must
have existed before this, as it is improbable that feathers and flight
were acquired at one bound, and this lends probability to the view that
at least some of the tracks in the Connecticut Valley are really the
footprints of birds. Not birds as we now know them, but still creatures
wearing feathers, these being the distinctive badge and livery of the
order. For we may well speak of the feathered race, the exclusive
prerogative of the bird being not flight but feathers; no bird is
without them, no other creature wears them, so that birds may be exactly
defined in two words, feathered animals. Reptiles, and even mammals, may
go quite naked or cover themselves with a defensive armor of bony plates
or horny scales; but under the blaze of the tropical sun or in the chill
waters of arctic seas birds wear feathers only, although in the penguins
the feathers have become so changed that their identity is almost lost.
[Illustration: Fig. 13.--Archaeopteryx, the Earliest Known Bird. _From
the specimen in the Berlin Museum._]
So far as flight goes, there is one entire order of mammals, whose
members, the bats, are quite as much at home in the air as the birds
themselves, and in bygone days the empire of the air belonged to the
pterodactyls; even frogs and fishes have tried to fly, and some of the
latter have nearly succeeded in the attempt. As for wings, it may be
said that they are made on very different patterns in such animals as
the pterodactyl, bat, and bird, and that while the end to be achieved is
the same, it is reached by very different methods. The wing membrane of
a bat is spread between his out-stretched fingers, the thumb alone
being left free, while in the pterodactyl the thumb is wanting and the
membrane supported only by what in us is the little finger, a term that
is a decided misnomer in the case of the pterodactyl. In birds the
fingers have lost their individuality, and are modified for the
attachment or support of the wing feathers, but in Archaeopteryx the hand
had not reached this stage, for the fingers were partly free and tipped
with claws.
[Illustration: Fig. 14.--Nature's Four Methods of Making a Wing. Bat,
Pterodactyl, Archaeopteryx, and Modern Bird.]
We get some side lights on the structure of primitive birds by studying
the young and the earlier stages of living species, for in a very
general way it may be said that the development of the individual is a
sort of rough sketch or hasty outline of the development of the class of
which it is a member; thus the transitory stages through which the chick
passes before hatching give us some idea of the structure of the adult
birds or bird-like creatures of long ago. Now, in embryonic birds the
wing ends in a sort of paw and the fingers are separate, quite different
from what they become a little later on, and not unlike their condition
in Archaeopteryx, and even more like what is found in the wing of an
ostrich.
Then, too, there are a few birds still left, such as the ostrich, that
have not kept pace with the others, and are a trifle more like reptiles
than the vast majority of their relatives, and these help a little in
explaining the structure of early birds. Among these is a queer bird
with a queer name, Hoactzin, found in South America, which when young
uses its little wings much like legs, just as we may suppose was done by
birds of old, to climb about the branches. Mr. Quelch, who has studied
these curious birds in their native wilds of British Guiana, tells us
that soon after hatching, the nestlings begin to crawl about by means of
their legs and wings, the well-developed claws on the thumb and finger
being constantly in use for hooking to surrounding objects. If they are
drawn from the nest by means of their legs, they hold on firmly to the
twigs, both with their bill and wings; and if the nest be upset they
hold on to all objects with which they come in contact by bill, feet,
and wings, making considerable use of the bill, with the help of the
clawed wings, to raise themselves to a higher level.
[Illustration: Fig. 15.--Young Hoactzins.]
Thus, by putting these various facts together we obtain some pretty good
ideas regarding the appearance and habits of the first birds. The
immediate ancestors of birds, their exact point of departure from other
vertebrates, is yet to be discovered; at one time it was considered that
they were the direct descendants of Dinosaurs, or that at least both
were derived from the same parent forms, and while that view was almost
abandoned, it is again being brought forward with much to support it. It
has also been thought that birds and those flying reptiles, the
pterodactyls, have had a common ancestry, and the possibility of this is
still entertained. Be that as it may, it is safe to consider that back
in the past, earlier than the Jurassic, were creatures neither bird nor
reptile, but possessing rudimentary feathers and having the promise of a
wing in the structure of their fore legs, and some time one of these
animals may come to light; until then Archaeopteryx remains the earliest
known bird.
In the Jurassic, then, when the Dinosaurs were the lords of the earth
and small mammals just beginning to appear, we come upon traces of
full-fledged birds. The first intimation of their presence was the
imprint of a single feather found in that ancient treasure-house, the
Solenhofen quarries; but as Hercules was revealed by his foot, so the
bird was made evident by the feather whose discovery was announced
August 15, 1861. And a little later, in September of the same year, the
bird itself turned up, and in 1877 a second specimen was found, the two
representing two species, if not two distinct genera. These were very
different from any birds now living--so different, indeed, and bearing
such evident traces of their reptilian ancestry, that it is necessary to
place them apart from other animals in a separate division of the class
birds.
Archaeopteryx was considerably smaller than a crow, with a stout little
head armed with sharp teeth (as scarce as hens' teeth was no joke in
that distant period), while as he fluttered through the air he trailed
after him a tail longer than his body, beset with feathers on either
side. Everyone knows that nowadays the feathers of a bird's tail are
arranged like the sticks of a fan, and that the tail opens and shuts
like a fan. But in Archaeopteryx the feathers were arranged in pairs, a
feather on each side of every joint of the tail, so that on a small
scale the tail was something like that of a kite; and because of this
long, lizard-like tail this bird and his immediate kith and kin are
placed in a group dubbed Saururae, or lizard tailed.
Because impressions of feathers are not found all around these specimens
some have thought that they were confined to certain portions of the
body--the wings, tail, and thighs--the other parts being naked. There
seems, however, no good reason to suppose that such was the case, for it
is extremely improbable that such perfect and important feathers as
those of the wings and tail should alone have been developed, while
there are many reasons why the feathers of the body might have been lost
before the bird was covered by mud, or why their impressions do not
show.
It was a considerable time after the finding of the first specimen that
the presence of teeth in the jaws was discovered, partly because the
British Museum specimen was imperfect,[6] and partly because no one
suspected that birds had ever possessed teeth, and so no one ever looked
for them. When, in 1877, a more complete example was found, the
existence of teeth was unmistakably shown; but in the meantime, in
February, 1873, Professor Marsh had announced the presence of teeth in
Hesperornis, and so to him belongs the credit of being the discoverer of
birds with teeth.