54 



THE QUARTERLY REVIEW OF BIOLOGY 



have been produced by the intercalation of 

 4 milk teeth in the series, if they were 

 found not to exceed n. The Miocene 

 genus Squalodon (Kellogg, 19x3) with its 

 telescoped and shortened braincase, lim- 

 ited facial depression, large temporal 

 fossae, heterodont dentition, and elon- 

 gated mandibular symphysis, is not un- 

 common in European and North Ameri- 

 can formations of Middle and Upper 

 Miocene age. Their skulls measured 

 about 3 feet in length, and according to 

 our present knowledge these squalodonts 

 scarcely attained a length of 1 6 feet. 



The slender-beaked Neosqualodon assen^ae 

 (Dal Piaz, 1904; Gemmellaro, 1911) rep- 

 resents one of the odontocete extremes 

 in the increase and elaboration of a 

 heterodont dentition. This extinct por- 

 poise was a member of the pelagic fauna 

 of the upper division of the Langhian 

 stage of the Lower Miocene and has been 

 found at two localities in Sicily. Fortu- 

 nately the left side of the skull and the 

 left mandible found in an asphalt pit in 

 the Tabuna region near Ragusa, province 

 of Siracusa, Sicily, are sufficiently com- 

 plete for the determination of the dental 

 formula. It is certain that Neosqualodon 

 has 3 incisors and 1 canine tooth in each 

 jaw, and that there are x6 cheek teeth in 

 the mandible. The skull was then fur- 

 nished with something like no teeth. 

 Each of the 10 posterior teeth in the 

 mandible has one or more accessory cusps 

 on the anterior and posterior cutting 

 edges. Some of the lower teeth have as 

 many as four accessory cusps on the an- 

 terior cutting edge. At least 7 of the 

 posterior maxillary teeth are serrated on 

 both cutting edges. The rostrum and 

 mandible are unusually elongated, and 

 the rostrum is fully three times as long as 

 the braincase. The braincase, so far as 

 known, is similar to Squalodon with the 

 narial passages moved backward beyond 



the level of the preorbital angles of the 

 supraorbital processes. The lachrymal 

 and the jugal with its long styliform 

 process are likewise similar. The skull 

 of Neosqualodon measures about 2.1 inches 

 in length. The subsequent history of this 

 series is unknown. 



The Miocene squalodonts seem to repre- 

 sent a line of development that was neither 

 antecedent to any group of modernized 

 porpoises nor adapted to environmental 

 conditions of the Pliocene. A late sur- 

 vivor, Frionodelfhis rovereti (Frenguelli, 

 19x2.), occurs in the estuary facies of the 

 Lower Pliocene Parana formation in the 

 province of Entrerios, Argentine Republic. 

 Judging from their shark-like teeth, these 

 squalodonts were well adapted for a pre- 

 daceous life, and hence could secure an 

 adequate food supply wherever fish or 

 small pelagic mammals were present in 

 sufficient numbers to insure easy capture. 

 Unless the prevailing pelagic conditions 

 were radically different during the Mio- 

 cene than at present, their distribution 

 should correspond in a general way with 

 that of the living killer whale (Orcinus). 

 Remains of squalodonts have been found 

 in Europe, North America, South America, 

 New Zealand, and Australia. 



Our knowledge of the Tertiary history 

 of the iniids is most unsatisfactory, 

 resting as it does upon a few imperfectly 

 preserved fragments of skulls of Miocene 

 and early Pliocene age . The teeth of these 

 iniids have lost their heterodonty, and 

 their cranial characters imply as long a 

 geological history as any of the extinct 

 porpoises associated with them during 

 Miocene time. 



Froinia fatagonica (True, 1909), which 

 was based on an imperfect crushed skull 

 and a single cervical vertebra obtained 

 from the Lower Miocene Patagonian 



