Popular Science Monthly/Volume 34/February 1889/Giant Reptiles of a Past Age
|GIANT REPTILES OF A PAST AGE.|
INDIANS of to-day, who are well acquainted with the history of their race, may often think with melancholy of the olden times, when their forefathers were the only masters of the country. Numerous and powerful tribes occupied the vast territory between two oceans, some hunting the deer in the forests of the East, others ruling supreme in the plains and mountains of the West. The white man was fighting hard for his existence in small settlements along the coast. But, whatever perfection in warfare and in the use of their weapons the Indians had acquired by the experience and practice of many generations, it was useless against the rising foe, who possessed and introduced entirely new arms and methods. And what is the result to-day? The majority of the tribes, and among them the most powerful ones, have been extinguished entirely; while others, sadly diminished in numbers, linger here and there, and the pale-face is met everywhere.
The same feelings of melancholy must enter the mind of an alligator of geological education, when, during a siesta in the sun, he thinks of the good old Mesozoic times and compares them with the pitiable present. "How beautiful were the Triassic and Jurassic periods, when numerous and powerful orders of reptiles were masters of the earth, when mosasaurus and other kings of the water were hunting the animals of the ocean, when gigantic dinosaurs reigned on the land, and pterodactyls populated the air! That parvenu, the mammal, was existing only in small species and struggling for an existence. But, alas! how is it now? Of our nine orders of reptiles five have disappeared entirely, among them just the most powerful ones, and only four are still in existence. Lizards, turtles, snakes, and we crocodiles have found refuge wherever we could, and mammals are met everywhere. And how did they succeed in thus becoming rulers of the earth? Simply by introducing new-fashioned arms and methods, such as warm blood and developed brains; and the most thickened bone plates and largest spines of our ancestors proved to be useless in the new kind of warfare." So Alligator Mississippiensis may meditate, and as a furious Apache Indian surprises and kills a lonely white squatter, so the alligator may rush upon and seize a strolling mammalian dog or pig of the nearest plantation.
The dinosaurs, one of the mentioned extinct orders of reptiles, were animals living on the land, some of them peaceably feeding on plants, etc.; others were dangerous carnivores. In form and size they showed differences as considerable as are presented among the existing mammals by the elephant and the mouse. While the smallest known dinosaurs were not larger than a fox, some of them attained a size which is almost fabulous, and a giraffe or an elephant would appear as a dwarf in comparison with these monsters. We may obtain a general idea of many dinosaurs if we imagine an animal like a huge crocodile, but with a smaller head, a longer neck, and posterior legs which are larger than the fore-legs. These larger posterior limbs, in connection with the long strong tail, gave to these animals somewhat the appearance of a kangaroo. Like this latter quadruped, they were occasionally sitting on the hind-legs and the tail, and some of them were probably also walking or hopping on their posterior legs. Instead of starting from a crocodile, we might therefore say: Let us imagine a huge kangaroo, where the difference between fore and hind legs, however, is not so great, and then let us transfer this into the reptilian system. For, while a kangaroo is a warm-blooded mammal, covered with hair, the dinosaurs were cold-blooded, scaly reptiles. The anatomy of the dinosaurs resembles that of the lizards and crocodiles, but in many respects it reminds us of the skeleton of birds. These bird-like features appear especially in the pelvis and the posterior legs, and are so striking that some scientists believe that birds are the descendants of dinosaurs; others think that birds and dinosaurs originated from a common ancestor. The close relationship of these two classes of animals will appear to us more plausible if we remember the fact that the birds of the Jurassic and Cretaceous periods resembled reptiles much more than they do now — for instance, in their possession of teeth. This may be said of dinosaurs in general, and we may now contemplate some of their known representatives.
If we enter the Museum of the Academy of Natural Sciences in Philadelphia, the first thing that attracts our eye is an Fig 2.-Hadrosaurus (restoration by Hawkins). enormous skeleton found at the left side of the entrance. It represents an animal seventeen feet high, and measuring from head to tail twenty-four feet. It is mounted so that it stands on its hind-legs and is supported by its strong and long tail, while the short anterior limbs rest upon a structure purporting to be a reproduction of a tree of past periods. If we examine the skeleton more closely, we find that only a few bones of the hind-legs and the tail are naturally found fossils, while all the other bones are artificial casts. But most of them are exact representations of the original fossil bones, which are kept under glass for the sake of better preservation. They were found in 1858 in the Cretaceous formation of New Jersey, and the animal has been described under the name of hadrosaurus. An exact imitation of this skeleton exists also in the National Museum at Washington.
The hadrosaurus is as yet the only complete mounted dinosaur in America, and it must not be forgotten that some parts of this skeleton were not found, but for the sake of completeness were formed in analogy to the others. In Europe they have been more fortunate in this respect. In the Royal Museum, at Brussels, in Belgium, there is the mounted skeleton of a similar dinosaur, the anatomy of which is almost as well known as that of a dog or a cat. This animal, the iguanodon, in the way it is mounted, reaches a height of about fourteen feet, and a length of nearly thirty feet. It also stands on the hind-legs, and is supported by the strong tail, which constitutes about a third of the whole length. The neck is erect, and the head horizontal, as if the animal were gazing forward. The short anterior limbs, somewhat bent, are hanging down. The hind-foot is composed of three strong toes armed with claws. The fore-feet have a long and strong spine where we have the thumb. The name of the animal has been chosen on account of its teeth, which resemble remarkably those of the Brazilian lizard, iguana, and indicate that the iguanodon was no carnivore, but a herbivorous
animal. It is thought that this animal lived in swamps or on the banks of rivers. It is further believed that it walked on its hind-legs, and that it treated its assailants in the way of a bear, by embracing them with its short and strong fore-legs, and piercing them by the dagger-like spines of the fore-feet.
Who were these assailants? Probably also dinosaurs belonging to the carnivorous branch of this order. One of the best known of them is the megalosaurus, an animal of about the same size and way of living as the iguanodon, marching or wading mostly on its hind-legs. A carnivorous animal is characterized
by its teeth, which must be apt to seize and lacerate its prey. The teeth of megalosaurus were few in number, large, flattened, of the shape of a saber, and with sharp, crenulated edges. Megalosaurus was a European dinosaur. One of the best-known American carnivorous dinosaurs of the Jurassic formation has been called ceratosaurus, on account of a large horn on the skull.
If the reptiles mentioned heretofore, with a length of twenty-five to thirty feet, must be called beasts of quite a respectable size, they were by no means the giants of their order. The largest known dinosaurs have been found in the Jurassic formation of the western slope of the Rocky Mountains, in Colorado and Wyoming. In the A Museum of Yale College, in New Haven, there are the vertebræ, limb-bones, etc., of the brontosaurus, which have been found in these beds. If, according to these remains, we make a restoration of the whole skeleton, the result is an animal of about sixty feet in length. But this is not all. The bone of the upper hind-leg, the femur, of the brontosaurus is smaller than six feet.
But in the same museum there is, besides other remains, the femur of a very similar dinosaur, found in the same beds, which is about eight feet long, and belonged to an animal the length of which has been estimated at from eighty to a hundred feet. It has been called atlantosaurus, on account of its size. This atlantosaurus must have been a beast able to sweep down an elephant with a stroke of its tail as a crocodile would a dog. Of all the known land-animals, living or fossil ones, it is the largest, and it is probable that Nature reached a limit in producing land-animals of this size.
If we compare with the atlantosaurus the smallest known dinosaurs, we find an enormous difference. In the lithographic lime-stones of Solenhofen, in Bavaria, which have yielded so many well-preserved and interesting animals of the Jurassic formation, a dinosaur has also been found. This animal, called compsognathus, had posterior legs which were much longer than the anterior limbs. It therefore probably walked or hopped on its hind-legs like a kangaroo or a bird, and altogether, with its long neck and small head, must have resembled a good deal the birds of the same period.
The name of dinosaurs means terrible saurians (δεινός, terrible); and, indeed, the aspect of animals like the atlantosaurus and others was probably such as to justify this name. One of the oddest-looking creatures of this order must have been an animal called
stegosaurus, the remains of which have also been found in the Western Jurassic and are preserved at the Yale College Museum. It was about twenty-five feet long. Its skull contained a brain which is comparatively the smallest brain which we know in any quadruped. It was, indeed, so small that it was probably not sufficient to control and direct all the nerves and muscles of the gigantic body. At any rate, we find in the stegosaurus that the vertebrae of the sacrum contain a cavity formed by an enlargement of the spinal canal. This chamber is ovate in form, and resembles the brain-case in the skull, but it is very much larger, being at least ten times the size of the cavity of the brain. Although we find in some animals a swelling of the spinal cord at the same place, there is nothing known which might be put beside the stegosaurus in this respect, and it is difficult to object if somebody claims that the animal possessed two brains—one in his skull and the other in his sacrum. The stegosaurus was, according to Marsh, protected and armed in the following way: At the region of the throat and low-er part of the neck there were small dermal plates in the thick skin, which were regularly arranged. The upper part of the neck was shielded by larger plates of the same kind, which were placed in pairs on each side. These plates of bone increased in size posteriorly, and covered the back. From the sacrum to the middle of the tail there was only one row of large scutes. At the end of the tail there were, as weapons of offense, several thick spines, about a foot long, so that a stroke of this tail must have been telling in its effects.
|Fig. 8.—Compsognathus (restoration by Huxley).||Fig. 9.—Foot-print of Brontozoum, one eighth natural size (after Hitchcock).|
We have now made the acquaintance of several dinosaurs, yet they are by no means all the members of this numerous order, upon which already a whole literature has been published. Some of them are known only by their foot-prints. The Triassic sand-stone of the Connecticut Valley contains numerous impressions of five-, four-, and three-toed dinosaurs, which at first were considered as the foot-prints of large birds. They were made when these animals walked on the muddy shores of the Triassic ocean. The collections of Amherst and Yale College contain each several thousands of such impressions—a fact that gives some idea of the abundance of reptilian life on the continent at that time. Also, in Europe, we find that reptiles, and among them especially dinosaurs, are the most numerous and dominating class of the Mesozoic times—that is, during the Trias, Jura, and Cretaceous; so that these times are often called the age of reptiles. At the end of the Cretaceous period, however, the reptiles decreased, and the dinosaurs became entirely extinct—at least, we do not know of any Tertiary dinosaur, and none exists at present.
Our knowledge of these remarkable animals is a comparatively recent one; of them almost nothing was known thirty years ago, but since then discoveries have followed each other in rapid succession, and every year contributes new data. It is especially to three American scientists that we owe most of our knowledge about dinosaurs; they are Prof. Joseph Leidy and Prof. E. D. Cope, in Philadelphia, and Prof. O. C. Marsh, in New Haven.