S 2 - 



THE QUARTERLY REVIEW OF BIOLOGY 



nerves leading to the "blow hole ap- 

 paratus." Similar foramina are present 

 in all known squalodont skulls. In the 

 progressive specialization and perfection 

 of the squalodont skull during Oligocene 

 time, the postorbital constriction was 

 eliminated by the exclusion of the parietal 

 bones from the vertex and the abutting of 

 the frontal bones against the upper border 

 of the supraoccipital. In the course of 

 this telescoping process the backward 

 overthrust of the maxillaries was con- 

 tinued until they met a barrier wall of 

 bone, the crest of the supraoccipital. 

 Hence in J all known squalodonts the 

 maxillaries are in contact posteriorly with 

 the upper border of the supraoccipital and 



goids and palatines similar to Globkefhala 

 but less telescoped, pterygoids forming 

 a sinus on each side in front of choanae 

 but without external reduplication, heter- 

 odont dentition, and the symphysis of 

 the mandible extending backward to the 

 level of the sixth tooth counting forward 

 from the last. Curiously enough these 

 short beaked squalodonts appear to be 

 restricted to the Southern Hemisphere, 

 where they have been found in association 

 with the more widely distributed long- 

 beaked types. Several fairly well pre- 

 served skulls of Prosqualodon australis 

 have been collected in Patagonia. An 

 exceptionally well preserved skull of 

 another species, Erosqualodon davidi was 



Squalodon bariense 

 Fig. 6. Lateral View of Skull of Squalodon bariense, Middle Miocene, France 



cover the underlying lateral extensions 

 of the frontal bones. 



Prosqualodon had 14 teeth in each upper 

 jaw and hence the total complement of 

 teeth would number 56, if the lower teeth, 

 which are not known, equal the upper. 

 The 3 incisor teeth are lodged in the 

 premaxillary bone as in other squalodonts. 

 Briefly stated this genus is characterized 

 by maxillaries extending backward be- 

 yond the premaxillaries and abutting 

 against the supraoccipital, a short broad 

 rostrum, a deep mesorostral trough, narial 

 passages nearly vertical, passages for 

 olfactory nerves separated by mesethmoid, 

 combined lachrymal and jugal wedged 

 in between maxillary and anterior margin 

 of supraorbital process of frontal, robust 

 zygomatic processes, relations of ptery- 



recently discovered at Wynyard, Table 

 Cape, Tasmania. 



The tendency of cetaceans descended 

 from the same stock to diverge in charac- 

 ter as they become specialized is well 

 illustrated by the short-beaked and long- 

 beaked porpoises which comprise the 

 family Squalodontidae. Inasmuch as 

 these squalodonts were already differen- 

 tiated into at least three distinct series 

 at the dawn of the Lower Miocene, their 

 predecessors must have flourished in the 

 Oligocene seas, yet the family appears to 

 have had but one survivor in the Pliocene 

 pelagic faunas. Very little is known in 

 regard to the geographic distribution of 

 the series typified by Prosqualodon and 

 Neosqualodon, yet Squalodon and its relatives 

 are known to have had a very extensive 



