BRAIN OF THE ZEUGLODONTID^. (537 



impossible to regard such later gigantic fortns as ancestral to 

 the later Squalodon series of animals, which appear to be more 

 definitely related to the progenitors of the modern Cetacea. 

 According to Winge (1919, 1921) Fraas "considered both Proto- 

 cetus and with it other Zeuglodonts as a side branch from the 

 Carnivores which did not lead in the direction of true whales." 



Stromer (1908, p. 174) also states: "Icli halte also einstweilen 

 fiir geboten die Zeuglodontidte flir eine ahnliche Parallelreihe der 

 Denticeten anzusehen, wie sie neuerdings innerhalb vieler eugeren 

 Saugethier-abtheilungen nochgewiesen wurden. Sie hatten schon 

 im Obereozan ihre Bliitezeit unter Entwickelung von Riesen- 

 formen wahx-end die anderen fast gleichartig aber viel weiter sich 

 differenzierend langsamer sich entwickelten und wieder in mehrere 

 Zweige auseinandergingen, die auch in vieler Beziehung einander 

 parallel fortliefen. In diesem Sinne also nehme ich wie Weber 

 (1886, S. 243) Zeuglodon als 'einen verunglUckten Yersuch 

 Cetaceen herau,szubilden ' lialto aber fih* noch nicht beweisen dass 

 alle Archajoceti so auf zufassen wai'en." 



■ Abel, in liis later works (1913), does not appear to have any 

 doubt that the Zeuglodontidro lie off the direct line, with the^ 

 possible exception of the so-called Microzeuglodontidfe. Because 

 of their great specialisation, the degree of which would entirely 

 unfit them for such an evolution, I am entirely in agreeiaient 

 with the opinion that no Zeuglodont here examined can be 

 regarded as ancestral to Cetacea. 



It is a curious fact that tliese highly specialised animals havei 

 so wide a geological distribution, and one in favour of their 

 marine life. This wide distribution may have occurred before- 

 the trigeminal specialisation, so characteristic of all these Fayum 

 forms, was attained. This makes the examination of the endo- 

 cranial casts in Zeuglodontida? found elsewhere in Europe, in 

 America, and in Australia of the greatest importance because the 

 facts put forward demonstrate ovir lack of knowledge concerning 

 the evolutionary history of the whales and also because " the 

 distribution of the Zeuglodontidse and other shallow- water fauna"" 

 has been used (Stromer, 1906, and Andrews, 1907) to indicate 

 the location of the shore-lines of previous land-connections 

 between the Old and New Worlds. I consider that in the 

 demonstration of this tactile specialisation in Zeuglodonts their 

 restriction to a shore-line distribution is shown to be highly 

 probable. ' • 



The parallel origin of the Zeuglodontidre and the Sirenia — 

 probably in the Lower Eocene — is very striking. The grade of 

 cerebral organisation in both is approximately similar, but the 

 cerebellum of Zeuglodontidro seems to indicate that its life was 

 somewhat less retired than that of Sirenia. Andrews (1907) has 

 shown that " freedom from competition and, to some extent, from 

 powerful enemies, Avould offer' exceedingly favourable conditions 

 for the rapid spread and multiplication" of these groups in the 

 Eocene seas. Thus both groups became widely disseminated, but 



