X.This is the initial stage of the True Elephant family, or more correctly, the transition from Mastodon to Elephant. The head is short and high, the lower jaw abbreviated, and the trunk fully developed and free to dangle to the ground. All trace of lower tusks had disappeared, and the upper ones are round and more or less up-curved. The number of molar teeth retained for active use, which in the astodon jaw was generally three and some times two, is in the case of the True Elephant family, reduced by one, and these teeth have increased in size.
Stegodon, the Gable-Toothed Elephant
Heretofore, all discussion of Mastodons has had to do with various kinds of paired-cones or crested molars; all of them long-rooted and more or less low-crowned. Such were browsing teeth suitable for soft green food but unsuitable for pulverizing or grinding hard tough substance such as dry grass or grain.
While the Mastodon star was in its ascendancy during the Pliocene period, and when hordes of these animals were wandering about the various countries of the earth, a small group of stay-at-homes in southern Asia, attracting no particular attention, were preparing a little surprise for the rest of the world. It was the old old story - a mere matter of teeth. Short-crowned, long-rooted molars with coned ridges composed of dentine and enamel had always been the Mastodon style. But the stay-at-homes in Asia were changing all this. Tooth height and substance and the coned ridges were pausing through a stage of transition represented by Stegodon, the Gable-toothed Elephant.
The rock-pages of the Himalayan Siwaliks record this transition in their upper layers. Occasional gaps are filled by missing pages found in China and Japan. It is in China particularly that we now hope to find many lost leaves of the race's history, not merely of Stegodon but of all stages from the primitive Mastodon down to the True Elephant.
Until 1921, knowledge of Chinese elephants has been denied us because of Oriental exclusiveness, which discouraged all efforts of foreigners to learn China's prehistoric secrets. Fossil bones were believed to have certain healing powers and so they were ground up and mixed with other ingredients to form medicines. However permission has recently been granted for foreigners to study the geology of China, and American scientists are now at work there searching for ancient animal remains. Bones of the Gable-toothed Elephant have already been exhumed and all gives promise of our learning much of the race's history, valuable information, no doubt, seeing that this region is generally recognized as the cradle of elephant development. For the moment, however, we must resort to the Siwaliks Hills rock-pages which, after telling of Trilophodon and Tetralophodon, open with the account of one whose molars had a thin coating of cement upon their surfaces. This latter substance overlying the enamel and dentine, was only a thin layer at first and destined to soon wear off when the tooth was used. But in proceeding upward or to the next stage, we find a later individual with more molar cement and five cross-crests instead of four. Above him lies one of a new type, upon whose teeth the cement has permanently established itself and the number of cross-crests augmented to six. These latter were of strange shape, each one being subdivided into roof-like prominences. This hitherto unknown style of molar crown marks the beginning of a modernized animal, Stegodon, which in Greek means "Gable-tooth," the name of this new elephant.
This beast was short-jawed and short-headed and presented a very mastodon-like appearance. His tusks were large, round and, although comparatively straight, were inclined to slight upward curvature. In some species, they were from eight to ten feet long. His body was large, his legs pillar-shaped and each round foot was equipped with five toes such as all mastodons had worn before him.
The Gable-toothed Elephant does not seem to have been as restless as his Mastodon forebears, for little is known about him except in Asia which, after all, was really the home and starting point of primitive elephants since early Miocene days. His bones and teeth are plentiful in northern India, Burma, southeastern China, Japan and even in the Island of Java, which was then joined to the Asiatic mainland. We are particularly interested in his Javan residency, meaning as it does that he was familiar with a very ancient - perhaps the most ancient known - prehuman being of the late Pliocene or early Pleistocene. This was the Java Man (Pithecanthropus Erectus or the Apeman-who-stands-erect), whose skull-cap, a few teeth and one thigh-bone were found in 1893 near the Solo River. Remains of several species of Stegodon lay in the rocks near the Java Man's bones.
The Stegodon was the connecting link between Mastodons and full-fledged elephants. Had his relics lain buried and lost to us in the great shadows of the Himalayas, we might to-day be merely speculating as to the Elephant's true origin. But the Siwaliks Hills discoveries remove all doubt. The teeth of Stegodon are there; the progress of development is beautifully protrayed, and the transition from Mastodon to Elephant is clearly established.
Continuing upward from our last stopping point, the Stegodon's progress can be readily followed. From six or more (Stegodon Cliftii) the transverse crests increase to nine (Stegodon Bombifrons) and finally to thirteen (Stegodon Insignis) and meanwhile the low-crowned, long-rooted grinder has assumed a higher-crowned, shorter-rooted appearance. Permanent cement is added to the valleys between crests until the surface when worn is quite flat; transverse lines of protruding enamel alternating with bands of dentine and cement. The columnar milling tooth is now formed, and the animal has become a grazer-eater of tough wiry grass. We turn to the final pages, the Upper Pliocene rocks of the Siwaliks and find ones with teeth of even more perfected form, such as appear in elephant jaws today. The transition is completed, for there lies a Mammoth (Elephas Planifrons) and above him, one of uncertain class (Elephas Hysudricus) both of undetermined family affinity but first of the True Elephants.
This is the final stage of Proboscidian development, and those who have followed the whole course from the Beast of Moeris to now, may be disappointed in its lack of continuity. They may have anticipated a sort of moving-picture show where the image registered on each film glides imperceptibly into the next. The impossibility of such a production might be due to the innumerable gaps awaiting filling in by discovery and would be in time completed, were there not other difficulties. The progression of the Elephant is one of stages, not individuals, and every stage can be traced - to more or less extent - back to a source where some of the other stages are independently registered. They may be likened to the branches of a tree whose trunk, representing the entire Proboscidian stock, found root in or before Eocene times. The Beast of Moeris, Ancient Mastodon, Phiomia and others not yet recognised were the largest and lowermost branches springing from the main stem. From one branch representing the Ancient Mastodon, for example, sprang other branches and from one of the latter sprouted a twig, the True Mastodon, and there matters ended. Another offshoot from the trunk may be represented by Phiomia in the Oligocene Period, and one springing from that, the Long-jawed Trilophodon. The Long-jawed Tetralophodon and Short-jawed Mastodon probably originated and ramified in the same way. There is no evidence that one stage evolved into the next, rather a succession of stages, each independently originated and one paralleling and finally supplanting the other. No Long-jawed Trilophodon became a True Mastodon and no Mastodon is known to have become an Elephant. Even as regards stages, the evidence is of Proboscidian development is too fragmentary to permit proof of unbroken continuity, even when stripped of its Dinotherium and other superfluous branches. This may in time be remedied, but meanwhile we can follow the Elephant's progress only by stages, where from a nondescript animal small although large for his time, he adopted a manner of living that best suited his initial tendencies. These tendencies encouraged the development of his muzzle into a flexible snout, his incisors into tusks and his molars into efficient grinders. Apparently the snout and molars counted most, but the development of the former produced chin and tusk exaggerations, as exemplified in the Long-jawed Trilophodon. These may be considered as errors, as was the pig-like molar tooth of the short-jawed Mastodon. And yet these various animals were not obliged to pay summarily for their mistakes. They disappeared as being departures from the general plan, but they must have been cared for and encouraged for they lived long lives, and their exit was slow and gradual, such was the experience of even those who followed the straight path; not such a very complicated plan when you reconsider it, this development of a nose into a trunk, incisors into tusks and browsing into grazing teeth particularly when several million years were allotted to its accomplishment. The complications are in the innumerable ramifications which took nlace during
the process. Had those who erred, paid for their mistakes by immediate extermination, the matter would have been greatly simplified, and made easier the production of a continuous picture. But the inborn power of adaptibility held good in all cases. Each erring one adjusted himself to the new life, best suited to his altered condition, and survived through countless centuries to a ripe old age, and yet leaving his mistakes multiplied a thousand-fold to confuse the palaeontologist. Is there any wonder then that even the expert often despairs of ever making the Story of the Elephant a continuous picture out of the mass of apparently hopeless confusion?
[from the original, typewritten draft with hand-written corrections - GL,III, ed.]