HISTORY OF WHALES 



53 



distribution. Prosqualodon is the best 

 known member of the short-beaked series. 

 Phoberodon and Squalodon may be taken as 

 typical representatives of the least special- 

 ized long-beaked series, while Neosqualodon 

 with its elongated rostrum and excessively 

 increased dentition undoubtedly repre- 

 sents the most highly specialized series . 



The relations of the cranial bones in all 

 of the long-beaked squalodonts belonging 

 to the Phoberodon-Squalodon series appear 

 to be essentially the same, and they differ 

 from one another merely in certain minor 

 details. The slender rostrum is nearly 

 twice as long as the braincase. The 

 backward thrust of the rostrum has carried 

 the maxillary over the frontal considerably 

 beyond the level of the orbit, and its 

 posterior edge abuts against the supra- 

 occipital. The frontals, which lie under- 

 neath the maxillaries, are also in contact 

 posteriorly with the supraoccipital, and 

 the parietals are excluded from the vertex 

 of the skull. The mesethmoid divides 

 the frontal fontanelle into two orifices, 

 provides additional support for the vertex 

 of the skull, and forms a thin veneer of 

 bone around the dorsal and lateral faces 

 of the presphenoid between the narial 

 passages. 



For Phoberodon arctirostris (Cabrera, 19x6) 

 of the Lower Miocene Patagonian marine 

 formation of Chubut, a skull and nearly 

 complete skeleton are known. The tele- 

 scoping of the braincase and the contours 

 of the entire skull are similar to Squalodon, 

 but the zygomatic processes are much more 

 robust. If the presence of rudimentary 

 basal cusps on the penultimate maxillary 

 molar and the two posterior mandibular 

 molars has any deep seated significance, 

 the dentition of Phoberodon must be con- 

 sidered as more primitive than that of 

 Squalodon. Cabrera contends that the 

 dental formula of Phoberodon should be 

 written as follows: I. 3/3; C. 1/1; Pm. 



6/6; M. 5/3 = 56. It is at least certain 

 that this squalodont had 11 trenchant 

 cheek teeth in each upper jaw and 9 in 

 each lower jaw. The high and rather 

 narrow scapula has a large broad acromion 

 and a small coracoid process. The hu- 

 merus has assumed the peculiar form of 

 living odontocetes. The cervical verte- 

 brae are free. The vertebral column is 

 incomplete, but Cabrera concluded that 

 this porpoise must have had 7 cervical, 

 9 dorsal, 12. lumbar, and 18 or 2.0 caudal 

 vertebrae. 



The genus Squalodon first makes its 

 appearance in the upper division of the 

 Lower Miocene in Italy near Belluno, 

 where two species have been recognized. 

 According to Dal Piaz (191 6), Squalodon 

 bariense with 58 teeth occurs only in the 

 lower level of the Upper Langhian stage 

 and the second species, Squalodon bellu- 

 nense, with 56 teeth in the upper level. 

 The teeth of Squalodon are increased above 

 44, the typical eutherian number, and 

 consequently have been the subject of 

 varying interpretations. Dal Piaz con- 

 tends that 8 or 9 of the cheek teeth are 

 premolars and that the molars may vary 

 from 1 to 3 . On the other hand, Van 

 Beneden, Zittel, and others have inter- 

 preted the cheek teeth as comprising 4 or 5 

 premolars and 5 to 7 molars. Whatever 

 may be the correct interpretation of the 

 dental formula, the cheek teeth in the 

 upper jaw of Squalodon are known to vary 

 from 10 to XT. and in the lower jaw from 

 9 to 11. At least 62. teeth were present in 

 the skull of Squalodon zitteli (Paquier, 

 1894; Zittel, 1876-77), a Middle Miocene 

 species found in the neighborhood of the 

 village of Bleichenbach in lower Bavaria. 

 This squalodont had ii cheek teeth in 

 each upper jaw. This is especially [inter- 

 esting in view of Winge's suggestion 

 (1911, p. 2.4) that the increase in cheek 

 teeth above the typical number 7 might 



