67. 



THE QUARTERLY REVIEW OF BIOLOGY 



slender ventrally directed dactyloid process 

 of the squamosal. The unusual size of 

 the air-sac at the outer side of the ptery- 

 goid, which is shaped to fit it, is another 

 peculiarity of modernized ziphioid skulls. 

 The base of the pterygoid has spread 

 laterally, covering or nearly covering the 

 alisphenoid bone, but the external redu- 

 plication is reduced to a low ridge. The 

 cervical vertebrae tend to ankylose with 

 one another. The dorsal, lumbar, and 

 caudal vertebrae have high neural spines 

 for the huge muscle masses associated 

 with the caudal flukes. The wrist and 

 finger bones are relatively small. 



It would appear that the Lower Miocene 

 ziphioids stand nearer to the squalodonts 

 than to the sperm whales. In the past 

 the beaked whales have been regarded 

 as near relatives of the physeteroids, a 

 conception which is disputed by Miller 

 (19x3), who calls attention to important 

 morphological differences, such as the 

 relation of the pterygoids to the palatines, 

 and the structural features of the vertex. 



DELPHINIDAE 



The obliteration of the postorbital 

 constriction by the exclusion of the par- 

 ietals from the vertex and the accompany- 

 ing contact of the supraoccipital with 

 the frontals was brought about by a 

 crushing together of the anterior and pos- 

 terior elements of the skull. This stage 

 of telescoping was fully established in 

 the odontocetes of the Lower Miocene. 



Scarcely less interesting than the fore- 

 going is the fact that the maxillary had 

 already reached its extreme posterior 

 extension in the squalodonts Ehoberodon 

 and Erosqualodon, the ziphioid DiochoPichus, 

 and the delphinoid Argyrocetus. In all 

 of these Lower Miocene South American 

 porpoises the orbital cavity and the 

 temporal fossa are roofed over by two 

 flattened plates of bone, the uppermost 



being the maxillary and the lowermost 

 the lateral extension of the frontal. The 

 temporal fossa has not suffered any marked 

 reduction because of any actual increase in 

 size of the braincase. In only one of the 

 preceding genera, Diocbotichus, do the nasal 

 bones retain a trace of their earlier function 

 of providing a roof for the nasal cavity. 

 What is of greatest interest, however, is 

 the entire absence of any indication of 

 heterodonty in these ziphioid and delphi- 

 noid types, and the fact that the premax- 

 illaries project anteriorly beyond the 

 maxillaries in all of these extinct por- 

 poises. All of these genera, without 

 exception, show that the narial passages 

 have been forced backward against the 

 anterior wall of the braincase and that 

 their inclination is determined by the 

 contour of this surface. 



According to Miller (192.3) the family 

 Delphinidae comprises five distinct sub- 

 families, which he designated as follows: 

 Delphininae, Eurhinodelphininae, Sten- 

 odelphininae, Delphinapterinae, and 

 Monodontinae. The validity of the sub- 

 family Eurhinodelphininae is somewhat 

 doubtful, for it includes extinct porpoises 

 in which the premaxillary is said to have 

 been lengthened so that it projects con- 

 spicuously in front of the maxillary for a 

 distance equivalent to one-fifth of the 

 total, a condition that is not apparent in 

 American specimens determined as- 

 Earbinodelfhis. The long beaked Lower 

 Miocene porpoise Argyrocetus has been 

 referred to this group by Cabrera (1916). 

 As a general rule among more recent 

 delphinoids the extreme tip of the pre- 

 maxillary tends to lose its position on 

 the ventral face of the rostrum because of 

 the forward extension of the underlying 

 maxillaries, and the teeth which were 

 originally implanted in it are lost. A 

 wide variety of extinct and living por- 

 poises (True, 1889) are included in the 



