SKULL OF DINOTHERIUM GIGANTEUM. 5;i3 



ligament. This flattening of the occiput, combined with its 

 forward inclination, must have made it possible for the animal to 

 move its head up and down through a large arc, a movement 

 perhaps connected with the use of the downwardly directed lower 

 tusks. The great width of the proboscis, probably rendered 

 possible by the absence of upper tusks, led to the widening out 

 of the skull in the orbital region, producing the shelf-like 

 projection of the maxillae above noticed. The great width of the 

 glenoid surface for the mandible is a peculiarity for which it is 

 difficult to account, unless it is correlated with the general 

 widening of this region of the skull. 



The skeleton of Dinotherium is still very imperfectly known, 

 but such bones as have been described show that the animal must 

 have been quite Elephantine in structure and appearance excej)t 

 as to its hea.d, the legs being pillar-like and the neck short. A 

 femur probably associated with the skull above described measured 

 150 cm. in length. The numerous speculations as to the appearance 

 and habits of Dinotherium have been summarized by de Blainville 

 and Stefanescu in their works referred to above. Most writers 

 seem to suppose that the animal was cJuefly fluviatile and 

 aquatic in its habits, but there appears to be no good reason for 

 believing that it Avas more so than the Elephants. 



The origin of Dinotheriumi is a question of much obscurity. 

 The genus must have branched off from the main Proboscidean 

 stem at a very early date, probably originating from an a.nimal in 

 much the same stage of evolution as Moeritheriuvn, the teeth being 

 still simply bilophodont. The premolar series is more highly 

 modified than in Mceritherium, the series being reduced to pm. 3 

 and pm. 4, the latter being bilophodont like the postei-ior molars. 

 This modification of the premolars, like the acquisition of the third 

 ridge in m. 1 and the reduction of the heel of m. 3, may have 

 arisen after the divergence from the majn stock had taken place. 

 It is interesting to note that the last lower milk molar of 

 Mceritherium shows a strong tendency to trilophodonty, the 

 posterior ridge being fairly distinct : in Dinotherium also this 

 tooth is trilophodont. If, as seems almost certain, Dinotherium 

 originated from some small comparatively generalized type, it is 

 interesting to note how, after its separation from the main stock, 

 the direction of evolution is almost the same as in the latter. 

 Thus there was a _ general increase in stature, which, being 

 accompanied by a shortening of the neck, necessitated, as in the 

 Elephants and Mastodons, the development of an elongated 

 snout ; so that it ma}'' be regarded as certain that Dinotherium 

 passed through a longirostrine stage comparable to that of 

 which the beginning is seen in Palceomastodon and the culmina- 

 tion, so far as the elongation of the lower jaw is concerned, in 

 Tetrahelodon angustidens. Subsequently the symphysis became 

 somewhat shortened and was deflected, the lower incisors at the 

 same time becoming enlarged. It is interesting to notice that a 

 tendency to a similar type of modification of the mandible occurs 



