THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 313 



a hippopotamus {H. hipponensis) } It is noteworthy that this species of 

 hippopotamus is recorded (Gaudry, 1876) also in the Phocene or early 

 Pleistocene of Algeria and in the Siwalik Hills of India. 



Outside of Casino, Italy has thus far proved barren of remains of the 

 'ancient Pliocene fauna,' with the exception of a few scattered fossils be- 

 longing to the following characteristic Pliocene species: 



(1) Mastodon arvernensis, the mastodon of the Val d'Arno. 



(2) Dicerorhinus leptorhinus, a rhinoceros of Sumatran type, successor 

 to the Upper Miocene types. 



(3) Sus strozzii, a wild boar. 



(4) Tapinis arvernensis, a tapir which persists through the Pliocene. 



Hippopotami. — The sudden appearance of hippopotami in Europe is 

 one of the most striking features of Lower Pliocene times; it is comparable 

 to that of the sudden appearance of mastodons in Lower Miocene Europe. 

 The presence of these animals in Casino is attested by Deperet (1890) and 

 by Schlosser (1887), the species being described as H. hipponensis; an allied 

 form is found in Algeria. These animals are abundant in the Phocene of 

 the Siwaliks of Asia at this time (p. 329). 



The origin of the hippopotami is still unknown. Stehlin- (1908) has 

 suggested that possibly the Eocene Choeromorus survived beyond the con- 

 fines of Europe and gave rise to the hippopotami. The affinity of the 

 Siwalik Merijcopotamus, an animal first described as Hippopotamus by Fal- 

 coner and Cautley, but now placed near the anthracotheres, would appear 

 to suggest an anthracotheroid origin for the hippopotami. 



They certainly enjoyed a wide range in Pliocene times from southern 

 Asia to southern Europe and northern Africa. The prevailing Pleistocene 

 species is the giant form known as H. major, found in the Upper Pliocene 

 and Pleistocene of Algeria, in southern and central Europe, and in England. 

 The existing African species {H. ampkibius) is also recorded by some authors 

 in the Pleistocene. The difference is probably only a matter of terms. There 

 are also the dwarf species H. pentlandi, H. minutus, occurring in the isolated 

 islands of the Mediterranean.^ 



Middle Pliocene or Astian 



This stage contains the continuation of the 'foune pliocene anciemie' of 

 Deperet. Geologically the period is characterized by a gradual recession 

 of the sea and increasing and more widespread fluviatile and freshwater 

 depositions. Fortunately these depositions are rich in mammalian life, so 



' Deperet, Les Aniniaux Pliocenes du Roussillon, 1890, p. 189. 



- Stehlin, H. G., Die Siiugetiere des schweizerischen Eocaens. Critischor Catalog der 

 Materialien. Fiinf ter Teil : Chceropotamus, Cehochaerus, Chceromorus, Haplohuriodon, Rhagath- 

 erium, Mixtotherium. Ahhandl. schiveiz. paldont. GeselL, Vol. XXXV, 1908, pp. 691-837. 



3 Von Zittel, K., Handbuch der Palaontologie, 1, IV, Mammalia, Munich, 1891-1893. 



