three-toed. It was intermediate between a Tapir and a Rhinoceros in size. It has been shown, too, from casts of the interior of the skull, that the cerebral hemispheres are much less convoluted than were those of Titanotherium.
Related to Palaeosyops is another primitive Titanothere, the genus Telmatotherium. This is also Eocene, from the Uinta Basin, the uppermost of Eocene strata. The skull of these creatures was rather elongated, and not unlike that of a Titanothere in general aspect. The dentition was complete and the canines not very large. The horns, which acquire so prodigious a development in the later Titanotheres, are just recognisable in at any rate many species of this genus Telmatotherium, the name being thus by no means an apt one. Better was that proposed by Dr. Wortman, of Manteoceras or "prophet horned." The horns are small elevations upon the frontals just at the junction of these with the nasals, and, indeed, lying partly upon the latter bones. In T. cornutum the horns are chiefly borne upon the very long nasals, whose size contrasts with the same bones in the more highly-developed Titanotherium. It appears to be quite possible that Titanotherium was evolved from the genus Telmatotherium.[[169]]
Sub-Order 9. LITOPTERNA.
Whether the Macraucheniidae should be considered as a separate group of Ungulata is a matter of dispute. Cope placed them in a special order of Ungulates which he called Litopterna. Zittel, on the other hand, regards them as definitely Perissodactyles. One curious point of resemblance to existing Horses is shown—that is the presence of a pit in the incisor teeth. This matter seems to be so important as to need a placing of these forms in the neighbourhood of the Perissodactyles, even of the Equidae; it is so peculiar a character, and apparently so little related to any obvious similarity in way of life, that it seems to mark a special affinity. Not so the fact that in Macrauchenia at any rate the orbit was entirely surrounded by bone as in the Horse. We find that condition so frequently acquired in many groups,—a development from an earlier condition where the cavity for the lodgment of the eye is in continuity with the temporal
fossa, that it cannot be regarded as anything more than a mark of specialisation. It is, in fact, the case that the Macraucheniidae are in many points specialised, while retaining many primitive features of structure.
The chief primitive features are: the non-alternating positions of the wrist- and ankle-bones; these, of course, interlock in the Perissodactyles of to-day and in many extinct families. Then the absence of a diastema in the tooth series, coupled with the presence in Macrauchenia of a complete dentition. The small brain may be referred to the same category. Macrauchenia must have been a strange-looking animal. It walked upon three toes on each limb; the skull was Horse-like in general form, but the nostrils are removed to a point about as far back as in the Whales or nearly so, the nasal bones being correspondingly reduced. This it is thought argues a proboscis. The humerus is particularly compared by Burmeister[[170]] to that of a Horse. The radius and ulna though both well developed are fused. The neck is long, and, as in the Camel, the vertebral arteries run inside the neural arches. Since the fore-legs seem to have been rather longer than the hind-legs, though only very slightly, and the neck was long, the animal may have presented some likeness to the Giraffe. It is interesting to note that in the proportions of humerus to ulna this animal is more Lama-like than Horse-like. On the other hand, the proportions of femur to tibia are more Horse-like. The remains of the creature are limited to South America, and to quite superficial deposits. It is evidently a specialised type, and has pursued a course parallel to that of the Horse. Much nearer to the Horse however, but apparently by convergence only, is the genus Thoatherium, usually placed in a separate family, the Protorotheriidae. In this creature, which has many archaic characters, the toes are reduced to one in each foot. In an allied form, Protorotherium, we have the two lateral toes diminishing just as in Anchitherium.