Animals of the Past

IV

History shows us how in the past nation after nation has arisen, increased in size and strength, extended its bounds and dominion until it became the ruling power of the world, and then passed out of existence, often so completely that nothing has remained save a few mounds of dirt marking the graves of former cities. And so has it been with the kingdoms of nature. Just as Greece, Carthage, and Rome were successively the rulers of the sea in the days that we call old, so, long before the advent of man, the seas were ruled by successive races of creatures whose bones now lie scattered over the beds of the ancient seas, even as the wrecks of galleys lie strewn over the bed of the Mediterranean. For a time the armor-clad fishes held undisputed sway; then their reign was ended by the coming of the sharks, who in their turn gave way to the fish-lizards, the Ichthyosaurs and Plesiosaurs. These, however, were rather local in their rule; but the next group of reptiles to appear on the scene, the great marine reptiles called Mosasaurs, practically extended their empire around the world, from New Zealand to North America.

We properly call these reptiles great, for so they were; but there are degrees of greatness, and there is a universal tendency to think of the animals that have become extinct as much greater than those of the present day, to magnify the reptile that we never saw as well as the fish that "got away," and it may be safely said that the greatest of animals will shrink before a two-foot rule. As a matter of fact, no animals are known to have existed that were larger than the whales; and, while there are now no reptiles that can compare in bulk with the Dinosaurs, there were few Mosasaurs that exceeded in size a first-class Crocodile. An occasional Mosasaur reaches a length of forty feet, but such are rare indeed, and one even twenty-five feet long is a large specimen,[4] while the great Mugger, or Man-eating Crocodile, grows, if permitted, to a length of twenty-five or even thirty feet, and need not be ashamed to match his bulk and jaws against those of most Mosasaurs.

The first of these sea-reptiles to be discovered has passed into history, and now reposes in the Jardin des Plantes, Paris, after changing hands two or three times, the original owner being dispossessed of his treasure by the subtleties of law, while the next holder was deprived of the specimen by main force. Thus the story is told by M. Faujas St. Fond, as rendered into English, in Mantell's "Petrifactions and their Teachings": "Some workmen, in blasting the rock in one of the caverns of the interior of the mountain, perceived, to their astonishment, the jaws of a large animal attached to the roof of the chasm. The discovery was immediately made known to M. Hoffman, who repaired to the spot, and for weeks presided over the arduous task of separating the mass of stone containing these remains from the surrounding rock. His labors were rewarded by the successful extrication of the specimen, which he conveyed in triumph to his house. This extraordinary discovery, however, soon became the subject of general conversation, and excited so much interest that the canon of the cathedral which stands on the mountain resolved to claim the fossil, in right of being lord of the manor, and succeeded, after a long and harassing lawsuit, in obtaining the precious relic. It remained for years in his possession, and Hoffman died without regaining his treasure. At length the French Revolution broke out, and the armies of the Republic advanced to the gates of Maestricht. The town was bombarded; but, at the suggestion of the committee of savans who accompanied the French troops to select their share of the plunder, the artillery was not suffered to play on that part of the city in which the celebrated fossil was known to be preserved. In the meantime, the canon of St. Peter's, shrewdly suspecting the reason why such peculiar favor was shown to his residence, removed the specimen and concealed it in a vault; but, when the city was taken, the French authorities compelled him to give up his ill-gotten prize, which was immediately transmitted to the Jardin des Plantes, at Paris, where it still forms one of the most interesting objects in that magnificent collection." And there it remains to this day.

The seas that rolled over western Kansas were the headquarters of the 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 vertebræ 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.

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]

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 vertebræ 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 zoölogical 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.

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 vertebræ 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 vertebræ 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 vertebræ. Not far away, however, was a big lump of stone containing several vertebræ of just the right size, and these were used as models to complete the papier-maché skeleton shown at Atlanta, in 1894. But a year after Mr. Schuchert collected a series of vertebræ, beginning with the tip of the tail, and these showed conclusively that the first lot of tail vertebræ 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.

V

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 Archæopteryx 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.

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 Archæopteryx the hand had not reached this stage, for the fingers were partly free and tipped with claws.

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 Archæopteryx, 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.

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 Archæopteryx 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.

Archæopteryx 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 Archæopteryx 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 Saururæ, 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.

The next birds that we know are from our own country, and although separated by an interval of thousands of years from the Jurassic Archæopteryx, time enough for the members of one group to have quite lost their wings, they still retain teeth, and in this respect the most bird-like of them is quite unlike any modern bird. These come from the chalk beds of western Kansas, and the first specimens were obtained by Professor Marsh in his expeditions of 1870 and 1871, but not until a few years later, after the material had been cleaned and was being studied, was it ascertained that these birds were armed with teeth. The smaller of these birds, which was apparently not unlike a small gull in general appearance, was, saving its teeth, so thoroughly a bird that it may be passed by without further notice, but the larger was remarkable in many ways. Hesperornis, the western bird, was a great diver, in some ways the greatest of the divers, for it stood higher than the king penguin, though more slender and graceful in general build, looking somewhat like an overgrown, absolutely wingless loon.

The penguins, as everyone knows, swim with their front limbs—we can't call them wings—which, though containing all the bones of a wing, have become transformed into powerful paddles; Hesperornis, on the other hand, swam altogether with its legs—swam so well with them, indeed, that through disuse the wings dwindled away and vanished, save one bone. This, however, is not stating the theory quite correctly; of course the matter cannot be actually proved. Hesperornis was a large bird, upwards of five feet in length, and if its ancestors were equally bulky their wings were quite too large to be used in swimming under water, as are those of such short-winged forms as the Auks which fly under the water quite as much as they fly over it. Hence the wings were closely folded upon the body so as to offer the least possible resistance, and being disused, they and their muscles dwindled, while the bones and muscles of the legs increased by constant use. By the time the wings were small enough to be used in so dense a medium as water the muscles had become too feeble to move them, and so degeneration proceeded until but one bone remained, a mere vestige of the wing that had been. The penguins retain their great breast muscles, and so did the Great Auk, because their wings are used in swimming, since it requires even more strength to move a small wing in water than it does to move a large wing in the thinner air. As for our domesticated fowls—the turkeys, chickens, and ducks—there has not been sufficient lapse of time for their muscles to dwindle, and besides artificial selection, the breeding of fowls for food has kept up the mere size of the muscles, although these lack the strength to be found in those of wild birds.

As a swimming bird, one that swims with its legs and not with its wings, Hesperornis has probably never been equalled, for the size and appearance of the bones indicate great power, while the bones of the foot were so joined to those of the leg as to turn edgewise as the foot was brought forward and thus to offer the least possible resistance to the water. It is a remarkable fact that the leg bones of Hesperornis are hollow, remarkable because as a rule the bones of aquatic animals are more or less solid, their weight being supported by the water; but those of the great diver were almost as light as if it had dwelt upon the dry land. That it did not dwell there is conclusively shown by its build, and above all by its feet, for the foot of a running bird is modified in quite another way.

The bird was probably covered with smooth, soft feathers, something like those of an Apteryx; this we know because Professor Williston found a specimen showing the impression of the skin of the lower part of the leg as well as of the feathers that covered the "thigh" and head. While such a covering seems rather inadequate for a bird of such exclusively aquatic habits as Hesperornis must have been, there seems no getting away from the facts in the case in the shape of Professor Williston's specimen, and we have in the Snake Bird, one of the most aquatic of recent birds, an instance of similarly poor covering. As all know who have seen this bird at home, its feathers shed the water very imperfectly, and after long-continued submersion become saturated, a fact which partly accounts for the habit the bird has of hanging itself out to dry.

The restoration which Mr. Gleeson has drawn differs radically from any yet made, and is the result of a careful study of the specimen belonging to the United States National Museum. No one can appreciate the peculiarities of Hesperornis and its remarkable departures from other swimming birds who has not seen the skeleton mounted in a swimming attitude. The great length of the legs, their position at the middle of the body, the narrowness of the body back of the hip joint, and the disproportionate length of the outer toe are all brought out in a manner which a picture of the bird squatting upon its haunches fails utterly to show. As for the tail, it is evident from the size and breadth of the bones that something of the kind was present; it is also evident that it was not like that of an ordinary bird, and so it has been drawn with just a suggestion of Archæopteryx about it.

The most extraordinary thing about Hesperornis, however, is the position of the legs relative to the body, and this is something that was not even suspected until the skeleton was mounted in a swimming attitude. As anyone knows who has watched a duck swim, the usual place for the feet and legs is beneath and in a line with the body. But in our great extinct diver the articulations of the leg bones are such that this is impossible, and the feet and lower joint of the legs (called the tarsus) must have stood out nearly at right angles to the body, like a pair of oars. This is so peculiar and anomalous an attitude for a bird's legs that, although apparently indicated by the shape of the bones, it was at first thought to be due to the crushing and consequent distortion to which the bones had been subjected, and an endeavor was made to place the legs in the ordinary position, even though this was done at the expense of some little dislocation of the joints. But when the mounting of the skeleton had advanced further it became more evident that Hesperornis was not an ordinary bird, and that he could not have swum in the usual manner, since this would have brought his great knee-caps up into his body, which would have been uncomfortable. And so, at the cost of some little time and trouble,[7] the mountings were so changed that the legs stood out at the sides of the body, as shown in the picture.

A final word remains to be said about toothed birds, which is, that the visitor who looks upon one for the first time will probably be disappointed. The teeth are so loosely implanted in the jaw that most of them fall out shortly after death, while the few that remain are so small as not to attract observation.

By the time the Eocene Period was reached, even before that, birds had become pretty much what we now see them, and very little change has taken place in them since that time; they seem to have become so exactly adapted to the conditions of existence that no further modification has taken place. This may be expressed in another way, by saying that while the Mammals of the Eocene have no near relatives among those now living, entire large groups having passed completely out of existence, the few birds that we know might, so far as their appearance and affinities go, have been killed yesterday.

Were we to judge of the former abundance of birds by the number we find in a fossil state, we should conclude that in the early days of the world they were remarkably scarce, for bird bones are among the rarest of fossils. But from the high degree of development evidenced by the few examples that have come to light, and the fact that these represent various and quite distinct species,[8] we are led to conclude that birds were abundant enough, but that we simply do not find them.

Several eggs, too—or, rather, casts of eggs—have lately been found in the Cretaceous and Miocene strata of the West; and, as eggs and birds are usually associated, we are liable at any time to come upon the bones of the birds that laid them.

To the writer's mind no thoroughly satisfactory explanation has been given for the scarcity of bird remains; but the reason commonly advanced is that, owing to their lightness, dead birds float for a much longer time than other animals, and hence are more exposed to the ravages of the weather and the attacks of carrion-feeding animals. It has also been said that the power of flight enabled birds to escape calamities that caused the death of contemporary animals; but all birds do not fly; and birds do fall victims to storms, cold, and starvation, and even perish of pestilence, like the Cormorants of Bering Island, whose ranks have twice been decimated by disease.

It is true that where carnivorous animals abound, dead birds do disappear quickly; and my friend Dr. Stejneger tells me that, while hundreds of dead sea-fowl are cast on the shores of the Commander Islands, it is a rare thing to find one after daylight, as the bodies are devoured by the Arctic foxes that prowl about the shores at night. But, again, as in the Miocene of Southern France and in the Pliocene of Oregon, remains of birds are fairly numerous, showing that, under proper conditions, their bones are preserved for future reference, so that we may hope some day to come upon specimens that will enable us to round out the history of bird life in the past.

REFERENCES

The first discovered specimen of Archæopteryx, Archæopteryx macrura, is in the British Museum, the second more complete example is in the Royal Museum of Natural History, Berlin. The largest collection of toothed birds, including the types of Hesperornis, Ichthyornis and others, is in the Yale University Museum, at New Haven. The United States National Museum at Washington has a fine mounted skeleton of Hesperornis, and the State University of Kansas, at Lawrence, has the example showing the impressions of feathers.

For scientific descriptions of these birds the reader is referred to Owen's paper "On the Archæopteryx of von Meyer, with a Description of the Fossil Remains, etc.," in the "Transactions of the Philosophical Society of London for 1863," page 33, and "Odontornithes, a Monograph of the Extinct Toothed Birds of North America," by O. C. Marsh. Much popular and scientific information concerning the early birds is to be found in Newton's "Dictionary of Birds," and "The Story of Bird Life," by W. P. Pycraft; the "Structure and Life of Birds," by F. W. Headley; "The Story of the Birds," by J. Newton Baskett.