126 



THE OLDEST MAMMALS. 



since a similar groove is found among existing mammals 

 only in the banded anteater and certain other carnivoi-ous 

 marsupials, we have pretty conclusive evidence that Tricon- 

 odon and its allies were really marsujsials. There can also 

 be but little doubt that the species of the amphitherian 

 type (I avoid mentioning the numerous genera of these 

 animals) are likewise members of the same order. It is, 

 however, quite possible that some of the Jurassic mammals 

 of Dorsetshire and North America may be more nearly 

 allied to that j'rimitive grouj) of mammals known as 

 Insectivores, among which are included the mole, the 

 shrew, and the hedgehog of Eiu-ope, as well as the more 

 generalized tenrec of Madagascar, and many other peculiar 

 creatures. All these insectivores are of a very low grade 

 of organization, and the result of modern researches is to 

 show that their connection with the marsupials is very 

 close indeed. Hence it is highl_y likely that some of the 

 Jurassic mammals may have been the actual connecting 

 links between the marsupials and the insectivores ; and it 

 is wortliy of mention here that while marsupials at the 

 present day linger on only in Australia and America, some 

 of the most primitive types of insectivores are preserved 

 to us in Madagascar, which is another refuge for animals 

 of a low grade of organization. 



There is yet fy^^Q^ 



another type of 



mammal found ,■- 



in the English \ 



and American \ 



Jurassics, to ^ 

 which the Micro - ;•""-•' 

 lestes of the trias \ 

 also appears to '■■■... 

 belong, which 

 has given rise to ^^t^- "^^ ■ — Lower Jaw of Plagiaulax ; natural 

 a vast amount size and enlarged. (After Marsh.) 



of discussion among the palaeontologists. These re- 

 markable mammals are mostly of very minute size, and 

 were long known only by their lower jaws, of which 

 a specimen is represented in Fig. 41, from which it will 



