HISTORY OF WHALES 



177 



by a corresponding decrease in the thick- 

 ness of the intervening septa. These 

 septa finally disappear, leaving an open 

 alveolar gutter in the maxillary. The 

 growth of the maxillary teeth is arrested, 

 and a hypertrophy of the dentition ensues. 

 Functional teeth are not present in the 

 upper jaw of the living sperm whale, 

 Physeter catodon, but as many as eight 

 atrophied teeth are sometimes found 

 buried in the gum. Conversely other 

 extinct types of physeteroids retain a 

 functional dentition in the upper jaws to 

 the close of their relatively brief life 

 span. The mandibular teeth of all known 

 physeteroids are implanted in distinct 

 alveoli. Whether or not a narrowing of 

 the mandibular symphysis brought about 

 an increased effectiveness of the teeth in 

 the lower jaws no one knows, but it is 

 nevertheless true that the great lateral 

 broadening out of the maxillary carried 

 the upper tooth rows outside of the normal 

 occlusal position of the upper and lower 

 cheek teeth. The teeth of these early 

 Miocene physeteroids are much larger 

 than those of contemporary odontocetes, 

 and it would seem that they were em- 

 ployed as much for tearing as for seizing. 

 Killer whales (Orcinus) tear away portions 

 of the flesh of their victims by quick 

 powerful jerks, and it is quite probable 

 that the earlier sperm whales tore their 

 food apart in a similar manner. It is 

 evident that the earlier Miocene delph- 

 inoids were likewise predacious, but their 

 slender teeth were adapted for seizing 

 and holding slippery prey, such as fish. 

 Two skulls, representing different genera 

 of physeteroids, are known from the 

 Lower Miocene Patagonian formation ex- 

 posed along the coast in Chubut Terri- 

 tory, Argentine Republic. The smaller 

 of these, Diaphorocetus poucheti (Moreno, 

 189Z) measured when complete about 

 three feet in length. It possessed teeth 



in both jaws, for which there were more 

 than 14 alveoli in each maxillary bone. 

 The occiput of this skull is obliquely 

 truncated, each maxillary bone is per- 

 forated by large foramina along the lateral 

 crest, the postnarial portion of the right 

 premaxillary is broad, forming the medial 

 surface of the posterior wall of the 

 supracranial basin, and the lateral margin 

 of the maxillary is not excessively thick- 

 ened above the supraorbital process. 



The other skull, representing Idioro-phus 

 patagonkus (Lydekker, 1894; Kellogg, 

 19x5), is nearly twice the size of that of 

 Diaphorocetus. It is characterized by the 

 number and position of the maxillary 

 foramina, the long laterally compressed 

 extremity of the rostrum with arched 

 premaxillaries, and the presence of teeth 

 in both jaws. There are 12. teeth in each 

 upper jaw, of which 19 are implanted in 

 the maxillary and 3 in the premaxillary. 

 Each mandible is provided with Z4 teeth. 

 The teeth average a little more than 4 

 inches in length, and their conical 

 crowns are covered with rugose enamel. 

 The long, terete, and but little curved 

 crowns are equivalent to a little more than 

 one-fourth of the total length of the teeth. 



The reduction of the maxillary dentition 

 had commenced as early as the Middle 

 Miocene, for we have indisputable evi- 

 dence that such was the case in the 

 Temblor Aulophyseter morricei (Kellogg, 

 19x7) found near Bakersfield, California. 

 The shallow closely approximated alveo- 

 lar grooves of the Temblor skull, occurring 

 as they do with other cranial details that 

 undoubtedly indicate a more advanced 

 stage in the basining of the facial region, 

 have suggested the possibility that if 

 teeth were present in the upper jaws they 

 were lodged in the gum as in the living 

 sperm whale. The skull measures about 

 four feet in length, and the distal constric- 

 tion of the rostrum is coextensive with the 



