THE PLIOCENE PERIOD. 327 



ford beds " as truly referable to this period, we meet at the 

 close of this period with shells such as nowadays are distinct- 

 ively characteristic of high latitudes. It might be thought 

 that the occurrence of Quadrupeds such as the Elephant, 

 Rhinoceros, and Hippopotamus, would militate against this 

 generalisation, and would rather support the view that the 

 climate of Europe and the United States must have been a 

 hot one during the later portion of the Pliocene period. We 

 have, however, reason to believe that many of these extinct 

 Mammals were more abundantly furnished with hair, and more 

 adapted to withstand a cool temperature, than any of their 

 living congeners. We have also to recollect that many of 

 these large herbivorous quadrupeds may have been, and 

 indeed probably were, more or less migratory in their habits ; 

 and that whilst the winters of the later portion of the Pliocene 

 period were cold, the summers might have been very hot. 

 This would allow of a northward migration of such terrestrial 

 animals during the summer-time, when there would be an 

 ample supply of food and a suitably high temperature, and a 

 southward recession towards the approach of winter. 

 The chief palaeontological interests of the Pliocene deposits, 

 as of the succeeding Post-Pliocene, centre round the Mammals 

 of the period ; and amongst the many forms of these we may 

 restrict our attention to the orders of the Hoofed Quadrupeds 

 ( Ungulates), the Proboscideans, the Carnivora, and the Quad- 

 rumana. Almost all the other Mammalian orders are more 

 or less fully represented 'in Pliocene times, but none of them 

 attains any special interest till we enter upon the Post-Pliocene. 

 Amongst the Odd-toed Ungulates, in addition to the remains 

 of true Tapirs (Tapirus Arverncnsis), we meet with the bones 

 of several species of Rhinoceros, of which the Rhinoceros Etrus- 

 cus and R. megarhinus (fig. 249) are the most important. The 

 former of these (fig. 249, A) derives its specific name from its 

 abundance in the Pliocene deposits of the Val d'Arno, near 

 Florence, and though principally Pliocene in its distribution, 

 it survived into the earlier portion of the Post-Pliocene period. 

 Rhinoceros Etrtiscus agreed with the existing African forms in 

 having two horns placed one behind the other, the front one 

 being the longest ; but it was comparatively slight and slender 

 in its build, whilst the nostrils were separated by an incom- 

 plete bony partition. In the Rhinoceros megarhinus (fig. 249, 

 B), on the other hand, no such partition exists between the 

 nostrils, and the nasal bones are greatly developed in size. It 

 was a two-horned form, and is found associated with ElepJias 

 meridionalis and E. antiquus in the Pliocene deposits of the 



