59 6 



HISTORICAL GEOLOGY 



because of the double-rooted back teeth, which present the appearance 

 of a yoke. The head of Zeuglodon was, in some cases, 4 feet long, 

 the length of the body 10 feet, while the tail was 40 feet long. The 

 animal (Fig. 538 A, B) was comparatively slender, an individual 



Fig. 538. — Skeleton and restoration of Zeuglodon. (Skeleton 



50 to 60 feet long having a thickness of only 6 to 8 feet. The teeth 

 are very unlike those of the primitive mammals, having been modified 

 for grasping and cutting. Back of the head were two short paddles 

 not unlike those of a fur seal, but the hind limbs were so reduced 

 that they were retained within the skin. 



The zeuglodonts were divers and probably lived upon squids, as 

 do the sperm whales to-day. The advantage of such a long tail in 

 proportion to the rest of the body has led to two suggestions : (1) with 

 it the animal could move at great speed through the water, perhaps 

 20 to 30 miles an hour; and (2), as far as definite evidence shows, the 

 tail may have been used quite as much for the storage of fat as for 

 propulsion. 



Ihe ancestry of the zeugolodonts has been traced back to a small 

 whale (Protocetus) with a skull about two feet long, in which the 

 teeth show a surprising resemblance to those of primitive carnivorous 

 land mammals (Creodonta). This whale has the typical number of 

 teeth (44) with one, two, or three roots, the dogteeth (canines) pro- 

 jecting beyond the others. Following these whales came others 

 (Eocetus) differing from those last described, in the fine, saw-edged 

 teeth. Probably descended from these (Eocetus) are others (Pro- 

 zeuglodon) in which the teeth depart widely from those of land 



