

HISTORY OF WHALES 



63 



family Delphininae, ranging in antiquity 

 from the Lower Miocene to the present 

 time. Extinct relatives of the Steno- 

 delphininae are not known with certainty 

 earlier than the Lower Pliocene. The 

 subfamilies Delphinapterinae and Mono- 

 dontinae have a shorter geological his- 

 tory, the occurrences being restricted to 

 the Pleistocene. One of the most remark- 

 able features of the odontocete skull is 

 its plasticity, which not only permitted 

 a reshaping of its contours in conformity 

 with environmental conditions imposed 

 upon it, but also in some instances seem- 

 ingly followed capricious paths of de- 

 velopment. The rostrum may be either 

 lengthened as in Cyrtodelphis or broadened 

 as in Globicephala, but it is never deepened 

 or solidified in the delphinoids. 



Porpoises with long slender rostra pre- 

 dominated in the pelagic faunas of the 

 Lower Miocene, as is evidenced by the 

 occurrence of Argyrocetm in Patagonia, and 

 Ziphiodelphis, Cyrtodelphis, Eoplatanista, 

 and Acrodelphis in Italy. The occurrence 

 of one little known, supposedly rather 

 short-beaked porpoise, Protodelphinus, near 

 Belluno was mentioned by Dal Piaz in 

 192.x. The skeleton of another short- 

 beaked porpoise, Delphinavus newhalli 

 (Lull, 1914), measuring about 5 feet in 

 length, has been found in the Lower 

 Miocene Vaqueros formation of San Luis 

 Obispo County, California. The skull is 

 eleven and a half inches long, three-fifths 

 of which is taken up by the rostrum. The 

 mandibular symphysis is relatively very 

 short, equivalent to slightly more than 

 one-eighth of the total length of either 

 ramus. It is interesting to note that the 

 premaxillary bone is toothless and that 

 the total complement of teeth is consider- 

 ably increased above the normal, there 

 being at least 180 teeth present. The 

 teeth are all alike, with slightly recurved 

 conical crowns covered with smooth 



polished enamel and no indication of 

 carinae. The cervical vertebrae are sep- 

 arate, and there are at least ix rib-bearing 

 vertebrae. The fore limb or pectoral 

 flipper is essentially delphinoid, with 

 modified carpal bones and the usual 

 arrangement of the metacarpals and 

 phalanges in the digits. From some such 

 type of extinct porpoise as this have de- 

 scended the living porpoises Delphinus and 

 Erodelphinus . In attempting to follow out 

 this subject of the late Tertiary history of 

 the delphinoids many equally interesting 

 types of extinct porpoises must be omitted, 

 and the interested reader is referred to 

 the bibliography for references to these 

 species. 



As with many other groups of extinct 

 mammals, we have an imperfect knowl- 

 edge of the earlier Tertiary history of the 

 long-snouted porpoises, which had al- 

 ready reached the fulness of their devel- 

 opment in the Lower Miocene. They 

 were then associated with several types 

 of undoubtedly carnivorous squalodonts, 

 but outlived most of them to find com- 

 panions in the even longer-snouted extinct 

 porpoises of the Upper Miocene. What- 

 ever their previous geological history 

 may have been, we are confronted in the 

 Lower Miocene with a highly telescoped 

 delphinoid type of skull, in which the 

 backward overthrust of the maxillary was 

 stopped by the crest of the supraoccipital 

 and the rostrum conspicuously elongated. 

 The splitting up of these long-snouted 

 porpoises into several series had already 

 commenced in the Lower Miocene, and 

 each of these phyla, as we shall presently 

 see, followed from then on their own 

 peculiar path of development. A brief 

 history of three of these series follows. 



The first to be considered is taken to 

 include the Lower Langhian Argyrocetm, 

 the Upper Langhian Ziphiodelphis, and the 

 Middle and Upper Miocene Eurhinodelphis . 



