HISTORY OF WHALES 



185 



anterior to the supraorbital processes. 

 The latter slant backwards and slope 

 from the interorbital region to the rim of 

 the orbit. The subsequent developmental 

 history of this family during the Miocene 

 is unknown. Several types of more 

 highly specialized balaenids such as 

 Balaenula balaenofsis (Van Beneden, 1878) 

 make their appearance during the Pliocene, 

 and their successors are the living genera 

 that comprise the family Balaenidae. 



NEOBALAENIDAE 



In the progressive specialization and 

 differentiation of the balaenid stock, two 

 or more trends of development were 

 followed, one of which resulted in the 

 elongation and lateral compression of the 

 rostrum as seen in the Balaenidae and the 

 other by a retention with very little 

 modification of the early cetothere type 

 of rostrum. The living pigmy whale 

 (Neobalaena marginatd) belongs to the 

 latter group. The rostrum of this whale 

 is very little longer than the occipital 

 shield and tapers rapidly from a broad 

 base to a slender tip. The mandible is 

 unusually robust and is strongly bowed 

 outward. The skeleton of this whale has 

 more peculiarities than any other living 

 mysticete. It has 17 pairs of large broad 

 ribs, of which at least eight are not 

 articulated. The seven cervicals are com- 

 pletely fused with one another. There 

 are 18 dorsal vertebrae, but no ribs are 

 attached to the first of the series. The 

 lumbar vertebrae have been reduced to one 

 or two, and the caudals do not exceed 

 14 in number. Future discoveries of 

 fossil mysticetes in the New Zealand and 

 Australian region should throw much 

 light on the developmental history of 

 'Neobalaena, which seems to be an offshoot 

 of some early stock that passed through 

 its development in the Southern Hemi- 

 sphere, following a somewhat different 



path from the balaenids, and acquired 

 peculiarities in the form of the ribs, the 

 vertebral column, and the hand. 



CETOTHERIIDAE 



If we take their features seriatim, we 

 find that the skulls of all known edentu- 

 lous Miocene cetotheres have supraorbital 

 processes that slope gradually outward 

 from the dorsal surface of the interorbital 

 region to the rim of the orbit and are never 

 abruptly depressed basally below the 

 level of the former as in the balaenopterine 

 whales. Many of these cetotheres 

 retained a well defined intertemporal 

 region, constituted entirely by the parie- 

 tals, which meet along the median line in 

 front of the supraoccipital shield. In 

 most species the braincase is short and 

 broad, but the supraoccipital shield is 

 quite variable in shape and extent, 

 depending in part upon the degree of 

 forward overthrust. The narrow ascend- 

 ing process of the maxillary is suturally 

 united with the mesial projection of the 

 frontal. The general arrangement of the 

 bones that inclose the narial passages is 

 more nearly in agreement with the 

 typical structure of terrestrial mammals 

 than with the toothed whales. The 

 nasal bones and mesial projections of the 

 frontals completely roof over the ethmoid 

 region and the dorsal nasal cavity, and in 

 addition the palatine is excluded from 

 the anterior wall of the corresponding 

 narial passage. The choanae lie behind 

 the anterior opening leading to the nostrils, 

 and the infraorbital plate of the maxillary 

 is retained. 



The skull of the Upper Oligocene 

 Cetotherio-psis lintianus (Meyer, 1849; 

 Brandt, 1873), found near Linz in Austria, 

 is characterized in part by a high narrow 

 triangular supraoccipital shield, which 

 curves more forward than upward and is 

 divided mesially by a long vertical 



