[Ill.u.s.tration: 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.
[Ill.u.s.tration: 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 cla.s.s of which it is a member; thus the transitory stages through which the chick pa.s.ses 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.
[Ill.u.s.tration: 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 Jura.s.sic, 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 Jura.s.sic, 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 cla.s.s 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.
[6] _The skull was lacking, and a part of the upper jaw lying to one side was thought to belong to a fish._
The next birds that we know are from our own country, and although separated by an interval of thousands of years from the Jura.s.sic Archaeopteryx, 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 pa.s.sed 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.
[Ill.u.s.tration: Fig. 16.--Hesperornis, the Great Toothed Diver. _From a drawing by J. M. Gleeson._]
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 att.i.tude. 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 Archaeopteryx 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 att.i.tude. 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 att.i.tude 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.
[7] _The mounting of fossil bones is quite a different matter from the wiring of an ordinary skeleton, since the bones are not only so hard that they cannot be bored and wired like those of a recent animal, but they are so brittle and heavy that often they will not sustain their own weight. Hence such bones must be supported from the outside, and to do this so that the mountings will be strong enough to support their weight, allow the bones to be removed for study, and yet be inconspicuous, is a difficult task._
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 pa.s.sed 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.
[8] _But three birds, besides a stray feather or two, are so far known from the Eocene of North America. One of these is a fowl not very unlike some of the small cura.s.sows of South America; another is a little bird, supposed to be related to the sparrows, while the third is a large bird of uncertain relationships._
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 a.s.sociated, 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 sh.o.r.es 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 sh.o.r.es 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 Archaeopteryx, Archaeopteryx 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 Archaeopteryx 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._
[Ill.u.s.tration: Fig. 17.--Archaeopteryx as Restored by Mr. Pycraft.]
VI
THE DINOSAURS
"_Shapes of all sorts and sizes, great and small._"
A few million years ago, geologists and physicists do not agree upon the exact number, although both agree upon the millions, when the Rocky Mountains were not yet born and the now bare and arid western plains a land of lakes, rivers, and luxuriant vegetation, the region was inhabited by a race of strange and mighty reptiles upon whom science has bestowed the appropriate name of Dinosaurs, or terrible lizards.
Our acquaintance with the Dinosaurs is comparatively recent, dating from the early part of the nineteenth century, and in America, at least, the date may be set at 1818, when the first Dinosaur remains were found in the Valley of the Connecticut, although they naturally were not recognized as such, nor had the term been devised. The first Dinosaur to be formally recognized as representing quite a new order of reptiles was the carnivorous Megalosaur, found near Oxford, England, in 1824.
[Ill.u.s.tration: Fig. 18.--Thespesius. A Common Herbivorous Dinosaur of the Cretaceous. _From a drawing by Charles R. Knight._]
For a long time our knowledge of Dinosaurs was very imperfect and literally fragmentary, depending mostly upon scattered teeth, isolated vertebrae, or fragments of bone picked up on the surface or casually encountered in some mine or quarry. Now, however, thanks mainly to the labors of American palaeontologists, thanks also to the rich deposits of fossils in our Western States, we have an extensive knowledge of the Dinosaurs, of their size, structure, habits, and general appearance.
There are to-day no animals living that are closely related to them; none have lived for a long period of time, for the Dinosaurs came to an end in the Cretaceous, and it can only be said that the crocodiles, on the one hand, and the ostriches, on the other, are the nearest existing relatives of these great reptiles.
For, though so different in outward appearance, birds and reptiles are structurally quite closely allied, and the creeping snake and the bird on which it preys are relatives, although any intimate relationship between them is of the serpent"s making, and is strongly objected to by the bird.
But if we compare the skeleton of a Dinosaur with that of an ostrich--a young one is preferable--and with those of the earlier birds, we shall find that many of the barriers now existing between reptiles and birds are broken down, and that they have many points in common. In fact, save in the matter of clothes, wherein birds differ from all other animals, the two great groups are not so very far apart.
The Dinosaurs were by no means confined to North America, although the western United States seem to have been their headquarters, but ranged pretty much over the world, for their remains have been found in every continent, even in far-off New Zealand.
In point of time they ranged from the Trias to the Upper Cretaceous, their golden age, marking the culminating point of reptilian life, being in the Jura.s.sic, when huge forms stalked by the sea-sh.o.r.e, browsed amid the swamps, or disported themselves along the reedy margins of lakes and rivers.
They had their day, a day of many thousand years, and then pa.s.sed away, giving place to the superior race of mammals which was just springing into being when the huge Dinosaurs were in the heyday of their existence.
And it does seem as if in the dim and distant past, as in the present, brains were a potent factor in the struggle for supremacy; for, though these reptiles were giants in size, dominating the earth through mere brute force, they were dwarfs in intellect.
The smallest human brain that is thought to be compatible with life itself weighs a little over ten ounces, the smallest that can exist with reasoning powers is two pounds; this in a creature weighing from 120 to 150 pounds.