IV.As previously noted, bones of Phiomia from the lower Oligocene of the Egyptian Fayum define this animal as one of primitive elephant stock and probably ancestral to a certain Miocene order of great numerical strength and wide distribution. Of the latter, the group best known is represented by the Long-jawed Trilophodon.
The Long-Jawed Trilophodon
This individual had an absurdly long spout-shaped chin tipped with two chisel-like tusks. His head was of only moderate length but two of the upper incisors had crowded all of the others out and developed into long tusks inclined forward and slightly downward. Because of his extraordinary development of the incisors, he is frequently spoken of as Tetrabelodon, a Greek name meaning four tusks. He was also a Trilophodon, for each second or intermediate molar tooth had three transverse crests, composed of paired cones standing side by side and partly joined together. The names Longirostris, long-jawed; Tetrabelodon, four-tusked and Trilophodon, three-ridged (molars) have all been applied to this animal and sound very confusing, but the early mastodons were so numerous and diversified that it is not easy to determine just how they are to be grouped. They may be better understood, however, if we bear in mind that mastodon progress had to do only with things pertaining to his head, particularly his nose and teeth. All else was subservient and, as far as his body and limbs are concerned, little or no change is recorded in the whole course of mastodon development.
Up to this stage, the race had never possessed less than four to six grinding teeth in each jaw at any one time but now the tendency is to employ larger teeth and fewer of them. The premolars were given up before maturity and only the molars retained. This new practice once established endured until the Mastodon's disappearance in Pleistocene times. It was a most decided departure from previous custom wherein the infant premolar teeth were in time replaced by a permanent outfit appearing vertically. The latter was the common mammalian method but this new one was an exception such as none but the Elephant family has ever attempted.
Although long-jawed, the Trilophodon was less so than appeared; for much of this extra length was taken up by his spout-shaped chin. The tooth-bearing portion was comparatively short, considering the size of the teeth, and mastodons generally favored big teeth. The result was that five or six of them could not be accommodated all at one time. Therefore, after the infant premolars were worn out and shed, new and permanent ones did not replace them. Up to this time, no molars had appeared, all jaw-space being taken up by the infant premolars. But when the first of the premolars was discarded, the other two slid forward and the first molar appeared in the rear of the jaw. This continued until all of the premolars had dropped out at the chin, leaving the three molars ensconced in their places. This method of replacement was therefore horizontal as compared with the old vertical method, each molar originating from a tooth-pulp cavity in the rear of each jaw. To be exact, the direction of replacement was the arc of a circle rising in the rear and falling at the front of the jaw. Although no more than three teeth were in place at any one time, each grinding tooth series numbered six, so that although the sum total of teeth and tusks was apparently no more than sixteen, it was in reality much greater, as no more than half of the grinder series was in use at any one time. When the first molar was worn out and shed, only the two molars remained and these had to do for the animal until he died. However this was no great hardship, for even when the jaw had its complement of three teeth, not more than two of them were being much used. No mastodon, long-jawed or otherwise, possessed canine teeth or incisors other than the four tusks and, as a rule, the first, sometimes two, of the four premolars in each jaw were missing.
The most persistent distinctions which may be depended upon for determining how the various early mastodons are to be grouped, are in the molar teeth and the second or intermediate one is the best for making comparisons. Upon examining the Long-jawed Trilophodon molar we find that the valleys between paired cones are partly obstructed by smaller cones, which combine to form a clover-leafed or trefoiled pattern. It is not the purpose here to go into the multiplicity of details as to the various spurs, and accessory cones which contribute to the structure of tooth crowns. All of them have meaning but only the more important distinctions need be considered. That his tooth-ridges numbered three and were trefoiled is sufficient to distinguish the Trilophodon from other mastodons.
The type and earliest known member of this order was the "Narrow-tooth" (Trilophodon Angustidens) found in the early Miocene deposits of Mogara, about seventy miles from the Egyptian Fayum region. The specific name Angustidens alludes to the beast's narrow molar teeth as distinguishing him from others with broader teeth. The two races of these animals, Broad- and Narrow-toothed, lived side by side in the Miocene of France. The Long-jawed Trilophodon was a well-armed and powerful beast about six feet tall with a thick-set body and pillar-shaped legs. As was the case with all mastodons, his feet were stumpy and the toes on each of them numbered five. Being well-equipped to feed and defend himself, he prospered. His home was in the lowlands near water where he used his lower jaws as a long-handled shovel and his upper tusks as pruning-knives to secure his food. These upper tusks were bordered with hard enamel on their lower sides so as to resist abrasion. These bands were very characteristic of Miocene mastodon tusks, being long, narrow strips of highly-polished enamel, one for each tusk extending from base to tip along the lower and outer side. Being of harder composition than the main body of the tusks, it was their duty to bear the brunt of wear which fell upon them when eating or while engaged in food-gathering. It may be inferred that the animal was by nature a digger and gardener, also that with his short neck, he might have had trouble reaching the ground, had not this contingency been forestalled by the lengthening of his upper tusks and lower jaws. He was also the proud possessor of a trunk - not a pretentious one, free to dangle; it was too short for that, and the long chin interfered; but it could at least flop around and slap at things and must have been of some assistance in food-gathering. The short nasal bones and backward position of the nares or nose-passages into the skull, tell us that much. It was a nose and upper lip combined, and the long spout-shaped chin formed a sheath to support it when at rest. The exaggerated length of the lower jaw was mostly a matter of this trunk-sheath. Long-chinned would therefore be a more appropriate term than long-jawed. The diploe or air-celled structure of his skull was an elephantine peculiarity that lay dormant in infancy but developed as the growing trunk and thickening neck muscles sought increased height of head for making their attachments. As the brain-case enlarged but little, the forehead was obliged to draw away from it, leaving diploe or bony cellular structure to fill up the space between. This expanding of the skull gave the animal an appearance of intellectuality, considerably more than that to which he was entitled.
In addition to his all-around ability at gardening, the Long-jawed Mastodon was a tireless traveller. Bones of the type, "Narrow-toothed" species (Trilophodon Angustidens) have been unearthed not only in Northern Africa but in Asia and Europe. A fine skeleton of him from the Miocene deposits of southern France is on exhibition in the Jardin des plantes Museum, Paris. In the middle Miocene deposits of northern India is found a variation of the type (Trilophodon Angustidens Palaeindecus), also a related species (Trilophodon Macrognathus). The land-route from Asia to North America, although a long one, must have been well travelled by the long-jawed beasts, for their remains have been met with in Texas, Nebraska, South Dakota, Maryland and Florida. A fine skeleton of the American type animal (Trilophodon Productus) is now on exhibition in the American Museum of Natural History, New York. This animal when alive must have been less than six feet tall at the shoulder, but another species from south Dakota (Trilophodon Gigantens), sometimes called Megabelodon, whose skeleton stands near by, was a much larger animal, also a very recent discovery. The two specimens are the only fairly complete ones in the United States and even in them, many bones are broken or missing and restored in plaster of Paris. In the South Dakota skeleton, the chin-spout or trunk-sheath is enormously developed so that the jaw is much longer than that of the smaller animal.
Species from Nebraska (Trilophodon Willistoni, Trilophodon Osborni, Trilophodon Lulli) are known only from their fragmentary bones and teeth. The race thrived in our country as in Europe and Asia, throughout the Miocene period and finally disappeared. The last known of it is (Trilophodon Floridanus) from the early Pliocene of Florida. There was another race of Trilophodons which for the lack of some other intelligent grouping must be here included. Its most distinctive characteristic was the absence of trefoils on its molar tooth surfaces. The American type (Trilophodon Serridens) from the late Miocene of Texas was long-jawed, and his upper tusks were protected by enamel bands. His successor (Trilophodon Praecursor) is found in the middle Pliocene of Texas. The Old World type (Trilophodon Turicensis) although a Trilophodon without trefoils on his molars, differed as to jaws. His chin was comparatively short and the lower tusks rudimentary. He was an African-Asiatic, who in middle Miocene times crossed the Mediterranean and entered Europe. Land-levels had arisen in those days and so he found a dry path to Sicily and then to Italy. Like all elephants in general, he was energetic and a born traveller. No doubt he had foresworn the gardening and digging habits of Long-jawed Mastodons, for his lower tusks were too small for use and his upper ones had a tendency to curl upward. This shortening of his lower jaws and tusks left his snout free to dangle and it must have served as a very useful grasping instrument. Probably he picked his food with his trunk instead of digging it, a new departure. This suggests that he was a forest-dweller which latter surmise is borne out by the fact that his bones are rare. Forest-animals are not commonly met with in geologically ancient deposits, for as a rule fluvatile, flood-plain and aeolian action are the forces that gather animal bones together beneath layers of sand, clay or gravel, hardening these layers into rock and sealing up the bones within. Forest animals are least subject to these forces of nature, whose effect upon wooded areas is less pronounced than upon lowlands and open country; and so when they die, their bones are scattered and in time disintegrate. Most of the Long-jawed Mastodons, whose remains have been found in abundance, were lovers of the lowlands and level open country free of large trees but covered with scrub and reeds. And so doubtless large numbers of the Trilophodon Turicensis species roamed over the Old World, but being forest-dwellers, their bones have not been well sealed up and preserved for inspection by later generations.
[from the original, typewritten draft with hand-written corrections - GL,III, ed.]