HISTORY OF MARINE MAMMALS—ABEL. 491 
While all the series thus far spoken of are still represented to-day, 
a fourth series, which also took its origin in the squalodons, is entirely 
extinct. This series comprises the long-beaked dolphins of the Upper 
Miocene of Antwerp (Lurhinodelphidw). In one species the snout 
reaches nine-elevenths of the total length of the skull, an enormous 
proportion, which stands alone among all the long-beaked aquatic 
animals which have lived hitherto. (Fig. 21.) 
The dolphins of the present are not the descendants of the squalo- 
dons. What their ancestors were we can not say to-day. It is sure, 
however, that they sprang from armored progenitors. In the Upper 
Miocene of Radoboj in Croatia a small-toothed whale closely allied 
to the harbor porpoise (Phocena) has been found whose whole flipper 
was covered with armor, while the existing harbor porpoise retains 
only scanty remains of this old armor. (Fig. 5.) 
Fie. 21.—Skull of a long-beaked dolphin. fuhinodelphis lengirostris Du Bus, from the 
Upper Miocene of Antwerp. Length of skull 106 em. (41.7 in.). 
The initial link for connecting the whalebone whales with the land 
carnivores is also wanting at present. Most probably they originated 
from the primitive cetaceans. But certainly they passed through the 
stages of toothed whales, as numerous denticles are present in the jaws 
of whalebone whale embryos. The oldest whales of this kind appear 
in the Miocene. They are very small, but approach very near the 
finbacks. 
While, therefore, the origin of some groups of whales is enveloped 
in obscurity, important and very rich discoveries in the Eocene of 
Egypt have shown us from what ancestors the sea-cows originated 
and how their stages of development proceed. 
Contemporaneously with the oldest primitive cetacean appears the 
oldest sea-cow, which has received the poetic name of the “ animal 
of the dawn,” Lotherium. With this appears a second, more highly 
developed genus, Protosiren. (Fig. 22.) The most salient character 
by which the oldest sea-cows are distinguished from the existing ones 
is the possession of all four limbs. The dentition is as complete as in 
the oldest primitive cetaceans. <A series of characters points with cer- 
tainty to a near relationship with the pachyderms. Elephants and 
sea-cows doubtless had the same ancestors. 
