Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/448

Rh 426 MAMMALIA [UNGULATA. Proboscideans for this molar to have more ridges than those which come behind it. The last milk molar has also three ridges, the pen ultimate but two. The cranium is much depressed, with compara- FIG. 104. Skull of Dinotherium giyanteum (Miocene, Eppe sheim). lively little development of air-cells. The remainder of the skeleton is imperfectly known, but apparently agrees in its general charac ters with that of the other Proboscideans. Remains of Dinotherium giganteum, an animal of elephantine pro portions, strikingly characterized by the pair of huge tusks descend ing nearly vertically from the front of the lower jaw, were first discovered at Eppels- heim, near Darmstadt, and described by Kaup. They have since been met with in various Middle and Upper Miocene forma tions in the south of Germany, France, Greece, and Asia Minor. Three species, D. pentapotamias, D. indicmn, and D. sindiense, have been, described by Falconer and Lydekker from north-western India. The genus has hitherto not been found in England or in America. The genus Phcnocodus, from the Lower Eocene of Wyoming, lately described by Cope (Am. Naturalist, December 1881 and June 1882), is placed by that zoologist in a special group called Condylarthra, allied to the Proboscidca, but distinguished by &quot;a post-glenoid process, and a third trochanter of the femur, and no calcaneal facet for the tibula. &quot; This and the Proboscidea are united by Cope to form the order Taxeopoda, one of his primary divisions of the Ungulate, In all the preceding forms the astragalus articulates only with the navicular bone, in those that follow with both uavicular and cuboid. SUBORDER AMBL YPODA. Among the most remarkable of the recent discoveries in the Eocene formations of the western States of North America has been that of a group of animals of huge size, approaching if not equalling that of the largest existing Elephants, presenting a combination of characters quite unlike those known among either recent or extinct creatures, and of which there were evidently many species living contemporaneously, but all of which became extinct before the close of the Eocene period. To form some idea of their appearance, we must imagine animals very elephan tine in general proportions and in the structure of their limbs. The fore foot had five, and the hind foot four toes. The tail, as in the Elephants, was long and slender, but the neck, though still short, was not so much abbre viated as in modern Proboscideans, and there is no evi dence that they possessed a trunk. The head differed greatly from that of the Elephants, being long and narrow, more like that of a Rhinoceros, and, as in that animal, was elevated behind into a great occipital crest, and it had developed upon its upper surface three pairs of con spicuous, laterally diverging protuberances, one pair in the parietal region, one on the maxillaries in front of the orbits, and one (much smaller) near the fore part of the elongated nasal bones. Whether these were merely covered by bosses of callous skin, as the rounded form and ruggedness of their extremities would indicate, or whether they formed the bases of attachment for horns of still greater extent, like those of the Rhinoceros or of the Cavicorn Ruminants, can only be a matter of con jecture. There were no upper incisors, but three on each side below, of comparatively small size, as was also the lower canine. A huge, compressed, curved, sharp-pointed canine tusk, very similar in form and position to that of the Musk-Deer, descended from each side of the upper jaw. These were present in both sexes, but very much smaller in the female, as was also the flange-like process of the lower jaw by which they were guarded. Behind these, and at some distance from them, were on each side above and below six molar teeth, of comparatively small size, placed in continuous series, each with a pair of oblique ridges conjoined internally and diverging exter nally in a V-like manner, and provided with a stout basal cingulum. The dental formula was therefore i %, c, p f , m | = 34; and the dentition had thus already attained a remarkable degree of specialization, although the brain was smaller and more rudimentary in characters than in almost any other known mammal. FIG. 105. Restoration of Dinoceras mirabile. J g nat. size. From Marsh (Am. Jour. Set., vol. xii. pi. 2). The first-discovered evidences of the existence of animals of this group were described by Leidy in 1872, under the name of Uinta- thcrium (from the Uintah mountains, near which they were found). Other nearly allied forms have been named Dinoceras (restoration of which is shown in fig. 105), Tinoccras, and Loxolophodon. They constitute the order Dinoccrata of Marsh, but are included by Cope in the Amllypoda. Another interesting form referred to this suborder is Coryphodon, which appears to connect the Proboscidca with the most primitive Perissodactyla, especially Lophiodon. It was first described by Owen in 1846 from a fragment of a jaw from the London Clay. More perfect remains were afterwards discovered in France, and lately in great abundance, indicating many species from the size of a Tapir to that of a Rhinoceros, in the lowest Eocenes of New Mexico and Wyoming, in the United States. It had forty-four teeth ; the canines of both jaws were large and sharp-pointed, and the molars had strongly pronounced oblique ridges. The general proportions were those of a Bear, but the tail was of moderate length, and the feet short and wide, with five toes on each. The Tertiaries of South America have yielded some very remark able forms of mammalian life, the nature and affinities of which