xi THE ODD- TOED UNGULATES 145 



To begin with the Perissodactyles. The earliest known 

 forms constitute a family called Lophiodontidw, composed of 

 the genera Lopliiodon, Coryphodon, and Hyracotherium. Of 

 these animals little is known except the teeth, which, however, 

 indicate rather a primitive or root form, from which, by 

 modification, all the other teeth of Perissodactyles can be 

 derived. The elevations and depressions of the molar teeth of 

 Lopliiodon, for instance, are arranged on a pattern which is 

 the best key to that of all others of the sub-order ; and it is 

 by going back, as it were, to it that we can understand and 

 compare all the other variously modified, and often more com- 

 plicated, forms. Moreover, these Lophiodonts possess a dental 

 character which distinguishes them from all other Perisso- 

 dactyles, and brings them into a more generalised ungulate type, 

 for which reason I place them nearest to the earlier forms 

 of artiodactyles that is, that all the premolars are smaller 

 and of a simpler form than the true molars. Whether they 

 possessed any modification of the limbs or other structures which 

 bear them out in this position, we unfortunately cannot say. 



At a somewhat later epoch in the earth's history appeared 

 on the scene the Palceotheriidce, an important group, containing 

 animals the osseous structure and dentition of which are 

 completely known, chiefly through the famous researches of 

 Cuvier into the fossils found in the gypsum quarries at 

 Montmartre. These were animals something like existing 

 tapirs, with three ioes on each foot, complete and distinct 

 radius and ulna and tibia and fibula, complete typical number 

 of teeth, i.e. i^c^-p^m^ = 44; but the molar teeth 

 modified in pattern from that of the Lophiodonts. They 

 flourished in the later eocene, after which period they are no 

 longer met with. They have been divided into several genera, 

 but Gaudry has shown that these are united by transitional 

 forms, and present a gradual series of modifications, corre- 

 sponding with successive geological epochs. Another offset, 

 from the ancient Lophiodont stock (with which it appears 

 to be connected through the American eocene Hyracahyus), 

 constitutes the family Tapiridce, first known in the miocene 

 and continued with scarcely any modification to our own day, 

 and therefore a most interesting form to contemplate in its 



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