HISTORY OF WHALES 



6 7 



Changes in the shape of the root, such as 

 may be observed when Eoplatanista is 

 contrasted with Cyrtodelphis, are compa- 

 rable to those in the teeth of very old indi- 

 viduals and mature specimens of the 

 living Platanista. At any event the 

 differences observed in the teeth are 

 hardly of sufficient importance to warrant 

 a family distinction between these two 

 extinct porpoises. The skull of Eoplata- 

 nista measured about x6 inches in length 

 and is thus a few inches shorter than that 

 of Cyrtodelphis. Its relationships appear 

 to be with Cyrtodelphis, and it is here 

 considered to be a member of that series. 



Extinct porpoises with similarly fash- 

 ioned jaws, such as Pomatodelphis (Allen, 

 19x1), which was characterized by a 

 somewhat narrower symphysis, were as- 

 sociated with Cyrtodelphis in these Miocene 

 seas. 



A third type of slender-beaked porpoise 

 is that described by Abel (1899) as Acro- 

 delphis, whose geologic range extends 

 from the Langhian to the Sarmatian in 

 Europe. As it is not the object of the 

 present summary to give a detailed de- 

 scription of each species, attention will 

 be directed to the characteristic features 

 of this extinct porpoise. The Lower 

 Miocene species, Acrodelphis krahulefxi 

 (Abel, 1899) from the Mugel-sands of 

 Gauderndorf, Austria, and Acrodelphis 

 ombonii (Longhi, 1898) from Libano, 

 Italy, show that this porpoise had 

 acquired a long narrow mandibular sym- 

 physis with acute posterior angle and a 

 large number of closely approximated 

 single-rooted teeth. The chief point of 

 interest in this group of somewhat smaller 

 slender-beaked porpoises is the pseudo- 

 heterodont appearance of the teeth. The 

 anterior teeth have a long slender crown 

 in contrast to the shorter, blunter, and 

 more incurved conical crowns of the 

 posterior teeth, which are further charac- 



terized by the presence of small accessory 

 tubercles, conspicuous basal rugosities, 

 and a crenelated cutting edge. The stage 

 of telescoping is similar to that of 

 Cyrtodelphis, but the vertex is smaller and 

 more convex, the frontals are restricted 

 to a narrow strip on the vertex, and the 

 nasal bones are relatively larger. Another 

 closely related porpoise, Champsodelphis, 

 was associated with it in the pelagic 

 faunas of the succeeding Miocene stages. 

 Like Cyrtodelphis, these extinct porpoises 

 seem to have left no descendants in the 

 later Tertiary. 



Modernized porpoises make their ap- 

 pearance in increasing numbers toward the 

 close of the Miocene epoch, and since that 

 time there has been relatively little modi- 

 fication of fundamental structural details. 

 These porpoises were followed by types 

 that resembled their progenitors in funda- 

 mental characters but differed in more 

 pronounced specialization of one or more 

 s tructures . The Pliocene period witnessed 

 the extinction of many aberrant and 

 highly specialized porpoises with ex- 

 tremely long rostra. Mechanical diffi- 

 culties apparently interfered with a 

 further development or even a continua- 

 tion of this type of rostrum. There are 

 brevirostrine and longirostrine types 

 among living porpoises, but none of the 

 latter approach these Miocene types in 

 the relative length of the rostrum. 



During the time of accumulation of 

 the Calvert formation in Maryland, several 

 types of short-snouted porpoises, in 

 association with some of the more highly 

 specialized long-snouted porpoises men- 

 tioned on the preceding pages, were 

 frequenting the estuary which covered 

 that area. Two of these porpoises are 

 represented in collections by nearly com- 

 plete skeletons, but the others unfortu- 

 nately are still imperfectly known. When 

 one studies the skulls of these extinct 



QUA.R. BEV. BIOL., VOL. Ill, NO. 1 



