THE elephants now to be found in Africa and India are similarly the results of a long Tertiary evolution. They appear to be descended from an animal like a tapir, which lived in the Fayum in Egypt during the earlier Oligocene times, one of the primitive hoofed animals not so distantly related to the original ancestor of the horses. This animal is named Mosritherium and, although in general features there is no similarity between its skull and that of the elephant, the position of the nostrils suggests that a short proboscis was already developed. In both the upper and lower jaws, the second incisor teeth are very strongly developed, forming little tusks which stretch forwards and so prolong the jaws.
The next stage is seen in an animal known as Palaomastodon, which is larger than Mceriiherium and already approaches the bulk of a small elephant. The skull and jaws show a similar advancement, the main features being the reduction of the nasal bones and retreat of the nostril opening, the lengthening of the incisors or tusks, and the presence of spongy bone in the back of the skull. The incisors of the lower jaw come together to form a shovel-like extension, and the molar teeth in the jaws have three transverse ridges. The next advance is to be found in Trilophodon, from the Miocene and Pliocene deposits of the northern hemisphere. Here the appearance and structure are much more like those of the true elephant. The air cells in the skull have become greatly increased, so that the skull is flat and somewhat domed. The upper and lower tusks are enormous and the great lower jaw projects far in front of
the upper. The teeth in the jaws have also become modified, for the skull of the adult has no pre-molars as the two molars completely fill the available room. Sometimes indeed there is only one molar. These molars are large, and the last has often so many as five ridges. The shovel tusk arrangement of the lower jaw was no doubt used for digging up vegetable food.
The next stage is Tetralophodon, found in Germany. The skull is much like that of the preceding form, but the teeth are more complicated in structure, and the lower jaw does not project so far in front of the upper. The lower tusks, too, are not close together and the fleshy proboscis would therefore hang down and probably was a real trunk, able to reach the ground, a feat the lower jaw was no longer able to perform. Then in Stegodon we reach the true elephants, for the lower incisors are lost and only the upper ones, the tusks, remain. The lower jaw is quite short, but the teeth are complex with many ridges.
Since the Pliocene period, many kinds of true elephants have lived and are known quite fully. The famous mammoth, of which complete specimens have been found in the frozen soil of Siberia, was a gigantic form with enormous curved tusks. Its teeth are commonly found and are really a series of compressed plates, the development of the ridges referred to in the earlier genera. Of all these elephantine forms only two, the African and the Indian, are present-day representatives.
The latest animals found in fossil form are mostly allied to, if not identical with, the living ones, and only the geographical distribution is changed.
In all these animals, we see that reaction to environment has been an outstanding factor, and only when we come to the highest of the mammals, Man, do we find one capable of altering conditions to suit his own limitations. So, the advent of Man, probably in Pliocene times, not only profoundly affected the contemporary and later faunas and flora, but modified some of the age-long natural laws as well.
WHAT TO READ NEXT
THERE are some fascinating and instructive books about animal life in prehistoric times and its remains, both for recreational reading and for practical assistance to the fossil hunter. Those who wish to follow up this article would do well to begin with Professor J. W. Gregory’s Geology (one of
books ABOUT ANIMAL LIFE OF THE PAST
Dent’s Scientific Primers), which is a simple and general introduction to Geology and the study of fossils for the beginner. An Introduction to Palceontology by A. Morley Davies (Murby) is an excellent general survey suitable for the amateur and specialist. A more specialised and entirely systematic work, very useful to the student, is Palceontology by E. Woods (Cambridge University Press). These three books deal principally with fossils of the invertebrate animals, although An Introduction to Palceontology includes a chapter on those with backbones.
Among the books that deal with the vertebrate fossils, the reader would do well to study the Natural History Museum’s Guide to the Fossil Mammals which, although essentially a guide book, is written in general terms to suit the visitor. It gives a clear idea of the relationships between the different fossil mammals. Vertebrate Palceontology by A. S. Romer (University of Chicago Press) is perhaps the best general book on the subject. It is suitable both for the interested amateur and the serious student.
‘Another of the Natural History Museum’s guide books, W. E. Swinton’s Guide to Fossil Birds, Reptiles and Amphibians, can be used as an elementary text-book. Monsters of Primeval Days, by the same author, contains a series of twenty-four half-tone plates, illustrating fossil reptiles and mammals as they lived. Each plate is faced by a page of simple explanatory notes, and a short general account of the subject is given in the preface. W. E. Swinton’s The Dinosaurs (Murby) is the only book on this subject, and is intended for both the layman and the student. It deals with every aspect of this great group of fossil animals.