THE DECAY OF THE GIANT BEASTS.
VISITORS to the Zoological Gardens and the Natural History Museum have doubtless sought some explanation of the monstrous skeleton of the iguanodon recently set up in the galleries at South Kensington, by inspecting the two large iguana lizards which have just arrived at the Zoo. The result is not likely to aid either scientific or unscientific inquirers in any great degree. The iguanodon was so named from the 'resemblance of its teeth—the first part of the skeleton discovered—to those of the iguana lizard ; and though this happy recollection, which occurred to Mr. Slutchbury when Dr. Mantell was searching the drawers of the Hunterian Museum for teeth resembling some which he had discovered in the Tilgate Forest, served to show that they belonged to some monstrous form of vegetable-eating lizard, there is not much else, in the form of the living iguana, to explain the mode of existence of a terrestrial lizard 30 ft. long, which fed on leaves like a giraffe, and walked or hopped on its hind- legs like a gigantic kangaroo.
The iguanodon was one among many huge extinct reptiles, some feeding wholly on vegetables, some on fish, while some were wholly carnivorous. So much can be gathered from the structure of their teeth. But this scarcely explains their place and function on the earth when they lived ; neither does it account for their enormous dimensions, the gradual decrease in the size of somewhat similar creatures of to-day, or, for the total disappearance of the greater number of types. The cir- cumstances of the discovery of the iguanodons, though interest- ing, throw little light on their habits, though one of the most interesting " finds " of recent days, in the eyes of paleontolo- gists. The character and probable size of the creatures had been accurately predicted by Sir Henry Owen, from fragments discovered by Dr. Mantel in the Weald of Sussex. But in 1878, in a clay-bed, 350 yards deep, in the workings of the Bernissart Colliery in Belgium, the skeletons of twenty-nine iguanodons were found together. It was not until seven years later that two were mounted in the courtyard of the Museum at Brussels; and the first which has been seen in England is only now exhibited at South Kensington. The
structure of the head and jaws shows that they had not only teeth adapted for vegetable feeding, but in all probability a prehensile tongue and lips, which enabled them to use their long necks for browsing on the tops of trees, just as the giraffe does. But the discoveries of
Professor Marsh in the " mauvaises terra " of North America, show that side by side with this " giraffe-lizard" were others which filled the places of the carnivorous land animals of our day, or haunted rivers and swamps, like the modern crocodiles. Others assumed bat-like forms, and were able to fly. Yet they in no case developed into higher forms, or presented any other than the common features of reptile-structure, modified for the part which they had to play in life. Their function was limited to that of "assuming some of the characteristics presented by animals much higher in the scale of being that flourish in the present day," showing what the Rev. H. A. Hutchinson has aptly called " a law of anticipation " rather than an example of progressive development.
The disproportion in size between so many of the creatures of the prehistoric world and of our own era, is more striking and less easily accounted for than the substitution of the more perfect forms of mammals for marsupials br gigantic lizards, having approximately the same functions. Not all the creatures of the epochs of gigantic animals were gigantic. Side by side with the iguanodon and its flesh - eating relations, the mososaurus and megalosaurus, there lived small quadrupeds, fish, dragon-flies, and other creatures not remarkable for size. Bat whether they assumed the charac- teristics of modern and more advanced species, as the can nivorous lizards did those of the carnivorous mammals, the fish-eating lizards those of the whales and sea-lions, and the leaf-eating iguanodons those of the giraffe, or were extinct members of existing species, such as the monster tortoises, the mammoths, and straight-tusked elephants, or the Bos urus and Irish elk of Great Britain, great size is the general con- comitant of great antiquity in early forms of living crea. tures. The fact is proved by their skeletons, and admits of no question. Yet each monstrous skeleton asks a very pertinent one. The globe was no larger then than the globe is now. There was no more surface space ; its natural features were probably on no larger scale than we see them to-day. The trees and grasses of the " Reptile Era " were not more luxuriant or of greater size than they are now. No fossil tree has been found as large as the " big trees of California ; and the " mares-tails " and tree-ferns which grew in the marshes and on the river banks were not more nutritious than the plants which form the food of the hippopotamus of to-day. Yet in a world of the same size, of not greatly different physical features, with no monstrous growth of plants, with water and atmo. sphere neither more nor less favourable to the growth of living tissues, one class of organic forms, the animals, were enor- mously larger than those of the present day, both in propor• tion to the rest of organic nature and to the actual surface of the globe on which they lived. Judged by the analogy of existing species, great size in animals must be supported by a correspondingly large food-supply, as well as by suitable climate. The former might be obtained either by limiting the number of the giant animals, or by increasing the area pro- ducing food available for their use. There is no reason to sup- pose that in the " Reptile Age," or even later, the giant forms were scarce. The number of iguanodons found together in the colliery may be cited as an instance, though the curious power of rivers to collect on one spot the dead carcases of creatures drowned over a wide area may partly account for their juxtaposition. But in the "mauvaises terms" west of the Mississippi Valley, old lake deposits of enormous size, the remains of gigantic creatures have been found in multi- tudes. They were not isolated gigantic individuals like the European elk, or even the Indian rhinoceros, but members of numerous, and in some cases of gregarious, tribes. The food necessary for the support of the non-carnivorous species was found, probably, not in a richer vegetation than now exists in tropical forests, or in an extent of the area of such vegetation beyond what is now found in the tropical and temperate zones, but in the practically undisputed possession which these creatures enjoyed of the whole of the earth's surface on which their food would grow. As higher forms of life successively became dominant, and took the place of those which had preceded them, the gigantic size remained fairly
constant. The degeneration in size and extinction of many of the larger species can be explained without reference either to natural catastrophes, or a gradual " freezing out " by the advance of glacial ice. There is no climatic reason why the monster elephants of the Sewalik Hills should not be found in the Indian jungles of to-day, or why the huge animals of primeval England should have been unable to exist in a climate which supported a hippopotamus identical with the African species, in the Midlands of Southern Britain. Man has been the unconscious, as well as the conscious, instrument in the whittling-down of animal size,—a result which can be detected almost immediately after his appearance on the scene.
The destruction of the gigantic animals of the later eras by the early bunting-races of mankind is the least part played by man in competition with existing animal forms. Hunting man does not, as a rule, increase in numbers. It was the gradual absorption by higher races than the cave-dwellers of the greater part of the natural feeding- grounds available for the support of the larger forms of animal life, which in the later era effected the gradual reduction in size. A subtraction sum showing the area which has been lost to the support of the great herbivorous creatures, either wholly, by cultivation, or partly by occupa- tion, hunting and the support of domestic animals, and transferred to the sole use of the one dominant race, would account sufficiently for the disappearance or degeneration in size of all the larger forms. The Bos taunts, whose enormous skeletons are in the British Museum, and the extinct bison, both of which were immensely larger than their modern repre- sentatives, the wild-cattle and the European anrochs, are in- stances of creatures which are known to have degenerated since the appearance of man. Restriction of range and of feeding- ground consequent on human encroachment are the only obvious explanations of this fact; and a similar loss of the necessaries of gigantic existence, due to other agencies, but identical in its effects, must account for the disappear. ance or degeneration of species more ancient than the human race.
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