220 R. S. Lull — Fossil Dolphin from California. 



pares favorably with the dolphins of this genus in point of 

 size, proportion of rostrum to cranium, in dental formula, char- 

 acter of the dentition, in having' approximately the same num- 

 ber of double-headed ribs, and in the general character of the 

 pectoral limb, more especially of the manus. 



The contrasts are in practically every instance clue to the 

 more primitive character of the fossil, and I fail to recognize 

 one which would debar the more ancient type from a direct 

 ancestry to Delphinus delphis itself. To^sum up these con- 

 trasts, they are : In the skull, the straighter, more nearly ver- 

 tical occiput, the minor proportions of the individual cranial 

 elements, the more robust zygomatic arch, the less expanded 

 maxillary plate, and the more broadly expanded and powerful 

 rear portion of the lower jaw. The cervical vertebrae, in so far 

 as may be learned, differ mainly in the lack of fusion of atlas 

 and axis in the fossil and the somewhat greater collective 

 length of the entire series. The dorsals are much longer in 

 centrum and lower in the height of the neural spine, while the 

 number of double-headed ribs in the two specimens is appar- 

 ently four for the fossil and five for the recent type, the only 

 instance wherein the former seems to be more specialized, and 

 this may be due to lack of perfection of the fossil. 



The sternum of the older form is simpler and more general- 

 ized, but easily modified into the modern type. In the limbs, 

 the contrasts lie in the less widely expanded scapula, relatively 

 longer humerus, wide lenticular space separating the radius and 

 ulna, and in the simpler form of the olecranon in the fossil. 

 In the carpus the magnum is relatively large, while in the 

 recent type it is vestigial. The phalanges are relatively longer 

 in the ancient type. 



The degree of evolution of the two dolphins is doubly inter- 

 esting when compared with the advance manifest in the same 

 length of time in certain terrestrial families, notably the horses. 

 It points to the early adaptation of the Cetacea to their aquatic 

 habitat and their slow subsequent evolution, which amounts, in 

 this instance, merely to the adjustment of certain minor details, 

 some, as in the jaw power, along the line of degeneracy, others 

 mainly for the perfection of speed. 



This evolution shows the impelling force of topographical 

 changes on the land, which not only directly modify the animal 

 form and motor organs, but also, through influencing climate 

 and thereby vegetative life, necessitate new adaptations on the 

 part of terrestrial animals or the elimination of those forms 

 which cannot thus change. All of this passes harmlessly over 

 the head of the cetacean, which can migrate when the waters 

 become too cold, and upon which none of the other influences 

 can make themselves felt. 



