

HISTORY OF WHALES 



fastened to the braincase, but is represented 

 as stopping at the level of the anterior 

 margin of the frontal, with no part of 

 this bone extending backward above the 

 supraorbital process. According to this 

 interpretation the rostrum was supported 

 solely by the vomer and the ascending 

 processes of the premaxillaries, which 

 extend backward to the parietals, a 

 mechanical arrangement that is not only 

 improbable, but structurally defective. 

 Professor Abel states that the postero- 

 internal extremity of the maxillary stops 

 at the antorbital line and does not push 

 backward across the supraorbital process 

 along with the ascending process of the 

 premaxillary, but instead slides under the 

 frontal. The last mentioned detail ap- 

 pears to be substantiated by the published 

 photograph and would indicate that an 

 infraorbital plate or process of the maxil- 

 lary was present. If the contact between 

 the frontal and maxillary has been cor- 

 rectly interpreted, the normal mammalian 

 relationship of these bones has been 

 retained, which furthermore is not 

 materially different from the relations 

 of these bones in Eubalaena and in the 

 zeuglodont type of skull. Granting that 

 the restoration represents the actual pres- 

 ent condition of the specimen, there is no 

 reason why the supraorbital process may 

 not have been narrowly margined ante- 

 riorly by a thin plate of the posterior end 

 of the maxillary, which was destroyed 

 without leaving any trace, if the connec- 

 tion between these elements was so 

 loose that no impression was made on the 

 upper surface of the frontal. According 

 to Konig (191 1), who was the first to 

 comment on this skull, its characters were 

 not very different from those of Agorophius, 

 on which the maxillary does overspread 

 the supraorbital process. This observa- 

 tion is disputed by Professor Abel (1924)- 

 Xenoropbus and Khacbianectes are the only 



QUA.R. EEV. BIOL., VOL. Ill, NO. 2 



known cetaceans in which it is apparent 

 that the maxillary does not reach postero- 

 internally as far back as the premaxillary, 

 but on both of these skulls the maxillary 

 has been thrust backward over the frontal. 

 It is stated that the lachrymal can be 

 seen from a ventral view in the antorbital 

 notch, but this bone is not so indicated 

 on any of the restorations. The dentition 

 is still functional in Patriocetus, and the 

 braincase is not materially unlike those of 

 generalized toothed whales, but the 

 periotic bone is of the mysticete type, 

 with long apophysis wedged in between 

 the exoccipital and squamosal. Patrio- 

 cetus appears to be a late Oligocene 

 survivor of an archaic family of cetaceans 

 that preceded the cetotheres. It is more 

 than likely that future discoveries will 

 show that this family contained types 

 directly related if not ancestral to the 

 succeeding edentulous cetotheres. 



As a basis for an interpretation of the 

 developmental history of the true mysti- 

 cetes we have seven genera of living whale- 

 bone whales and a rather large number of 

 fossil species ranging in age from Upper 

 Oligocene to and including the Pleisto- 

 cene. Many of them, however, are based 

 on very scanty remains. Starting with 

 the more generalized cetacean skull on 

 one hand and ending with the modernized 

 mysticete on the other, it becomes appar- 

 ent that the possibilities for remodeling 

 are limited to certain definite details and 

 that the fossil types represent successive 

 stages in the developmental history of 

 several phyla. If we based our deductions 

 solely on a critical comparison of the 

 Austrian Upper Oligocene and the Pata- 

 gonian Lower Miocene mysticete skulls, 

 we should be led to assume that the 

 forward overthrust of the posterior occip- 

 ital elements had precedence over the 





