Yet, strange to say, representatives of the higher creatures destined to inherit the earth at a later date actually existed. Toward the close of the Mesozoic we find birds approaching to those of our own day, and almost at the beginning of the time there were small mammals, remains of which are found both in the earlier and later formations of the Mesozoic, but which never seem to have thriven; at least so far as the introduction of large and important species is concerned. Traversing the Mesozoic woods, we might see here and there little hairy creatures, which would strike a naturalist as allies of the modern bandicoots, kangaroo rats, and myrmecobius of Australia; and closer study would confirm this impression, though showing differences of detail. In their teeth, their size, and general form, and probably in their pouched or marsupial reproduction, these animals were early representatives of the smaller quadrupeds of the Austral continent, creatures which are not only small but of low organisation in their class.
One of these mammals, known to us only by its teeth, and well named Microlestes, the “little thief” sneaks into existence, so to speak, in the Trias of Europe, while another very similar, Dromatherium, appears in rocks of similar age in America; and this is the small beginning of the great class Mammalia, destined in its quadrupedal forms to culminate in the elephants and their contemporaries in the Tertiary period. Who that saw them trodden under foot lay the reptile aristocracy of the Mesozoic could have divined their destiny? But, notwithstanding the struggle for existence, the weakest does not always “go to the wall.” The weak things of this world are often chosen to confound those that are mighty; and the little quadrupeds of the Mesozoic are an allegory. They may typify the true, the good, and the hopeful, mildly and humbly asserting themselves in the world that now is, in the presence of the dragon monsters of pride and violence, which in the days to come they will overthrow. Physically the Mesozoic has passed away, but still exists morally in an age of evil reptiles, whose end is as certain as that of the great Dinosaurs of the old world.
The Mesozoic mammals are among the most interesting fossils known to us. In a recent memoir by Professor Owen, thirty-three species are indicated—all, or nearly all, Marsupial—all small—all closely allied to modern Australian animals; some herbivorous, some probably carnivorous. Owen informs us that these animals are not merely marsupials, but marsupials of low grade, a point in which, however, Huxley differs somewhat in opinion. They are at least not lower than some that still exist, and not so low as those lowest of mammals in Modern Australia, the duck-billed platypus and the echidna. Owen further supposes that they were possibly the first mammals, and not only the predecessors but the progenitors of the modern marsupials. If so, we have the singular fact that they not only did not improve throughout the vast Mesozoic time, but that they have been in the progress of subsequent geological ages expelled out of the great eastern continent, and, with the exception of the American opossums, banished, like convicts, to Australia. Yet, notwithstanding their multiplied travels and long experiences, they have made little advance. It thus seems that the Mesozoic mammals were, from the evolutionist point of view, a decided failure, and the work of introducing mammals had to be done over again in the Tertiary; and then, as we shall find, in a very different way. If nothing more, however, the Mesozoic mammals were a mute prophecy of a better time, a protest that the age of reptiles was an imperfect age, and that better things were in store for the world. Moses seems to have been more hopeful of them than Owen or even Huxley would have been. He says that God “created” the great Tanninim, the Dinosaurs and their allies, but only “made” the mammals of the following creative day; so that when Microlestes and his companions quietly and unnoticed presented themselves in the Mesozoic, they would appear in some way to have obviated, in the case of the tertiary mammals, the necessity of a repetition of the greater intervention implied in the word “create.” How that was effected none of us know; but, perhaps, we may know hereafter.
THE MESOZOIC AGES (continued).
The waters of the Mesozoic period present features quite as remarkable as the land. In our survey of their teeming multitudes, we indeed scarcely know where to begin or whither to turn. Let us look first at the higher or more noble inhabitants of the waters. And here, just as in the case of the greater animals of the land, the Mesozoic was emphatically an age of reptiles. In the modern world the highest animals the sea are mammals, and these belong to three great and somewhat diverse groups. The first is that of the seals and their allies, the walruses, sea-lions, etc. The second is that of the whales and dolphins and porpoises. The third is that of the manatees, or dugongs. All these creatures breathe air, and bring forth their young alive, and nourish them with milk. Yet they all live habitually or constantly in the water. Between these aquatic mammals and the fishes, we have some aquatic reptiles as the turtles, and a few sea-snakes and sea-lizards, and crocodiles; but the number of these is comparatively small, and in the more temperate latitudes there are scarcely any of them.
All this was different in the Mesozoic. In so far as we know, there were no representatives of the seals and whales and their allies, but there were vast numbers of marine reptiles, and many of these of gigantic size. Britain at present does not possess one large reptile, and no marine reptile whatever. In the Mesozoic, in addition to the great Dinosaurs and Pterodactyls of the land, it had at least fifty or sixty species of aquatic reptiles, besides many turtles. Some of these were comparable in size with our modern whales, and armed with tremendous powers of destruction. America is not relatively rich in remains of Mesozoic Saurians, yet while the existing fauna of the temperate parts of North America is nearly destitute of aquatic reptiles, with the exception of the turtles, it can boast, according to Cope’s lists, about fifty Mesozoic species, many of them of gigantic size, and the number of known species is increasing every year When it is taken in connection with these statistics, that while we know all the modern species, we know but a small percentage of the fossils, the discrepancy becomes still more startling. Further, from the number of specimens and fragments found, it is obvious that these great aquatic saurians were by no means rare; and that some of the species at least must have been very abundant. Could we have taken our post on the Mesozoic shore, or sailed over its waters, we should have found ourselves in the midst of swarms of these strange, often hideous, and always grotesque creatures.
Let us consider for a little some of the more conspicuous forms, referring to our illustration for their portraits. Every text-book figures the well-known types of the genera Ichthyosaurus and Plesiosaurus; we need scarcely, therefore, dwell on them, except to state that the catalogues of British fossils include eleven species of the former genus and eighteen of the latter, We may, however, notice some of the less familiar points of comparison of the two genera. Both were aquatic, and probably marine. Both swam by means of paddles; both were carnivorous, and probably fed principally upon fishes; both were proper reptiles, and breathed air, and had large and capacious lungs. Yet with these points in common, no two animals could have been more different in detail. The Ichthyosaurus had an enormous head, with powerful jaws, furnished with numerous and strong teeth. Its great eyes, strengthened by a circle of bony plates, exceeded in dimensions, and probably in power of vision under water, those of any other animal, recent or fossil. Its neck was short, its trunk massive, with paddles or swimming limbs of comparatively small size, and a long tail, probably furnished with a caudal fin or paddle for propulsion through the water. The Plesiosaur, on the other hand, had a small and delicate head, with slender teeth and small eyes. Its neck, of great length and with numerous joints, resembled the body of a serpent. Its trunk, short, compact, and inflexible, was furnished with large and strong paddles, and its tail was too short to be of any service except for steering. Compared with the Ichthyosaur, it was what the giraffe is to the rhinoceros, or the swan to the porpoise. Two fishermen so variously and differently fitted for their work it would be difficult to imagine. But these differences were obviously related to corresponding differences in food and habit. The Ichthyosaur was fitted to struggle with the waves of the stormy sea, to roll therein like modern whales and grampuses, to seize and devour great fishes, and to dive for them into the depths; and its great armour-plated eyes must have been well adapted for vision in the deeper waters. The Plesiosaur, on the contrary, was fitted for comparatively still and shallow waters; swimming near the surface with its graceful neck curving aloft, it could dart at the smaller fishes on the surface, or stretch its long neck downward in search of those near the bottom. The Ichthyosaurs rolled like porpoises in the surf of the Liassic coral reefs and the waves beyond; the Plesiosaurs careered gracefully in the quiet waters within. Both had their beginning at the same time in the earlier Mesozoic, and both found a common and final grave in its later sediments. Some of the species were of very moderate size, but there were Ichthyosaurs twenty five feet long, and Plesiosaurs at least eighteen feet in length.