370 VERTEBRATE ZOOLOGY 



Family S. Phocidoe {The True Seals). — These animals have no ex- 

 ternal ears; the nostrils are dorsal in position; the hind limbs are in- 

 timately bound up with the short tail to make a sort of caudal fin, 

 which is used as a very effective swimming organ. The fore limbs 

 are rather small and fin-like, and the whole body is decidedly spindle- 

 shaped. The seals are much more highly specialized for marine life 

 than are either the sea-lions or the walruses. One of the commonest 

 of the seals is Phoca groenlandica (Fig. 190, D), a small spotted ani- 

 mal about four or five feet long. 



Extinct Carnivores 



Representatives of the Mustelidse have been found as far back as 

 Eocene times; some Canidse lived during Pliocene times. A whole 



Fig. 191.— Extinct carnivore, Smilodon. (From Lull, after Knight and Osborn.) 



family of cat-like creatures, the Machmrodontia, lived from Eocene 

 to Pleistocene times and are now extinct. The classic "saber-tooth" 

 (Smilodon) is a characteristic example of this rather remarkable ex- 

 tinct family (Fig. 191), which was characterized mainly by the ex- 

 treme modification of the teeth and skull in adaptation to the peculiar 

 method of attacking with the saber-like upper canines. These huge 

 teeth were thin and knife-like, with sharp edges. The method of 

 using these teeth was evidently quite different from that employed 

 by tigers; the prey was struck a downward, slashing blow, and was 

 probably stabbed as though by a dagger. The upper jaw was es- 

 pecially modified to support these huge canine teeth, and the skull 

 was radically altered to furnish attachment for the huge neck muscles 



