258 X AT URAL SCIENCE [October 



a condor, of whose size we may form an idea from the head, which 

 is much larger than that of a horse. 1 Being great runners, they 

 gave chase to the mammals of that epoch, even to the most gigantic 

 of them, and were doubtless not afraid to measure their strength 

 with the Dinosaurs themselves. 



But the animals of that period which in our formations offer 

 special interest are the mammals. While in Europe and North 

 America only some small representatives of that class lived, insig- 

 nificant and little specialised, in Argentina they had attained an 

 extraordinary development ; they were large and small, of the most 

 varied forms, showing that the Cretaceous deposits of our country 

 contain the ancestors of almost all the groups of mammals which 

 have succeeded each other one by one in different regions of the 

 earth. 



It would be a lengthy task to give you an account of the 

 mammalian fauna of that time ; it is only possible for me to outline 

 the subject and to limit myself to noticing some forms related to 

 others with which you are familiar. 



That which first attracts the attention of the naturalist in this 

 fauna is the presence of remains of the Primates or inferior quad- 

 rumana {Notopithccidae) of a greatly reduced size, which appear 

 to be the ancestors of the extinct lemurs of Europe and North 

 America, and of those existing in the South of Asia and Africa, 

 while another branch leads to the Homunculidae (Homunculus, 

 Anthropops, Pitheculus, etc.) of the Tertiary of our own country, 

 which are the ancestors of the monkeys of both worlds, and conse- 

 quently of man. 



The carnivorous mammals were represented solely by a group 

 to which I have given the name Sparassodonta, whose size varied from 

 that of a ' laucha ' (Pharsophorus) to that of the largest bear (Probor- 

 hyaena) ; they exhibit a mixture of the characters of placentals and 

 marsupials, and represent the stock whence were derived the car- 

 nivorous marsupials of the Australian continent, the placental 

 carnivores of both hemispheres, and a large number . of the extinct 

 forms of the northern hemisphere designated under the name 

 of Creodonts. 



Another most interesting group is that of the Plagiaulacoidea 

 {Polydolopidae, Abdcritidae, Epanorthidac, etc.), small marsupial 

 mammals with a dentition of the type of the Australian kangaroos, 

 but with the limbs more nearly equal, with five digits on each foot, 

 and with traces of syndactylism. They were extremely numerous, 

 and gave origin to the greater portion of the marsupials of Australia, 

 designated under the name of Diprotodonts, a group of which the 



1 These fossils may now be seen in the Department of Geology in the British Mnsenni 

 (Natural History). —Trans. 



