FOSSIL WHALES 383 



may be a colour adaptation. But the extant accounts of tlie 

 colour of tliis Dolphin vary — quite possibly in accordance with 

 real variations, such as are exhibited by Tnia already spoken of. 

 Pontoporia hldinvillii is a smallish Dolphin some 4 feet in length. 



Fossil Odontocetes. — Several of the existing genera of 

 Dolpliins are also known in a fossil condition, as well as 

 Ziphioid Whales closely related to existing forms. We shall 

 deal here only with a few genera of fossil Odontocetes wliich 

 depart in their structure from existing forms. 



The genus Physodon is Miocene, and has Ijeen found in 

 Patagonia. It appears to be most nearly allied to the Physeteridae, 

 but should probably form a distinct family. Physodon was not so 

 large as Physeter, the skull measuring only some 10 feet. It 

 tlius comes nearer in point of size to Kogia, and it is interesting 

 to note that its relatively-shorter snout is also suggestive of the 

 dwarf Cachalot. The general outline of the skull is, however, 

 more like that of Physeter, and tliere is the same deep cavity for 

 the lodgment of spermaceti. The main feature of interest in 

 the skull is the presence of teeth in both jaws, and tlie fact that 

 two or three are lodged in the premaxillae. This is precisely 

 what is found in the most ancient Whales, the Zeuglodonts. 



Extinct Dolphins, apparently referable to the Platanistidae, are 

 the most numerous among the earlier forms of Cetaceans, and it 

 is significant that the earliest known forms of these go back to 

 the Eocene. 



The genus Inio'psis of Mr. Lydekker,^ with one species, /. 

 cnucasica, comes from rocks which seem to be of that age. The 

 back part of the skull of this animal, tlie only part of the skull 

 known, has the same squarish excavation of the maxillaries that 

 characterises Inia and Pontoporia. Its lower jaw was slender 

 and possessed numerous teeth. 



The long snout and jaws of Platanistids, especially exaggerated 

 in Pontoporia among living forms, are constantly found in these 

 Tertiary Platanistids. 



Evrliinodelpliis had a beak three and a half times the length 

 of the cranium, whereas in Pontoporia the proportions are as 2:1. 

 The teeth too were very numerous. 



The genus Aryyrocetus, from Patagonian Tertiary strata, was 

 an animal about as large as the existing Dolphin. It had the 



i Proc. Zool. Sue. 1892, p. 558. 



