302 TYPES OF ANIMAL LIFE 



type of structure, the otter. It is possible, therefore, 

 that sea-lions and bears may have had one common 

 ancestor, and seals and otters another and distinct com- 

 mon ancestor. If so, much of that resemblance between 

 seals and sea-lions which is related to their similar aquatic 

 habits of life, may really have arisen independently, so 

 that they together form, in our own day, a much more 

 homogeneous group than they formed at some anterior 

 epoch. This, however, is mere speculation, and we are 

 far from wishing to insist upon even its probable truth. 

 It is an interesting possibility and no more. 



The argument against it is that bears seem to be a 

 very modern group of mammals, and it may be said that 

 both seals and sea-lions are descendants, not of any forms 

 which closely resemble existing land-Carnivora, but 

 rather of certain beasts, remains of which have been 

 found deep down in tertiary strata in the Eocene for- 

 mations of Europe and North America and which are 

 known to naturalists as the " Oreodonta." Such creatures 

 have been closely studied in America by Professor Cope, 

 and it may turn out not only that they were the common 

 ancestors of the existing Pinnipeds and land Carnivores, 

 but also of the whole of those much more divergent 

 groups, which together constitute the ordinary or pla- 

 cental mammals of to-day, together with the pouched 

 beasts which are distinguished from them as Didelphous 

 mammals,* as was explained at some length in our article 



on the opossum. 



* Sec p. 62. 



