INTEODTJCTION. xxvii 



beds oi Necrolestes, apparently a close ally of the Cape Golden Moles, and of the 

 Sparassodonta, which, after all, seem to be Creodonts and not Marsupials. Further- 

 more, light is also thrown on the numerous points of similarity between Strutbiones 

 and the Ehese, especially when it is remembered that a large Ratite bird, JSremo^ezus, 

 existed in the Eocene of Africa. As to the Ungulates, it seems likely that the 

 separation of the two areas took place when the main divisions were only just 

 beginning to be differentiated, and that groups like the Pyrotheria and the Archseo- 

 hyracidse are not ancestral to the Proboscidea and Hyracoidea of the Old World, 

 but more probably represent terms of partly parallel series which had a common 

 ancestry on the common land-surface before the separation of the two regions took 

 place. If this were so, we should expect to meet with a general resemblance between 

 the various groups rather than a close similarity of structure, and this, in fact, is what 

 we find. In the case of the occurrence of the primitive Sirenian Prorastomus in the 

 West Indies, and of the Water-Snake Pterosphenus in the Eocene beds of Alabama, 

 it seems likely that these animals passed either along the southern coast of the 

 Eocene Atlantic or across the bridge of shallow water between the chain of islands 

 above referred to as probably lying between West Africa and Brazil. The fact that 

 the mammalian fauna of Madagascar is a comparatively poor one and entirely 

 lacking in many of the groups that must have inhabited the Ethiopian mainland, is 

 considered by TuUberg to be accounted for by supposing that the eastern part of 

 Africa with Madagascar was separated from the main South-west African continent by 

 an arm of the sea, and that it was not till after the isolation of Madagascar (probably 

 in the late Oligocene) that the two portions of Africa became united. At this time 

 East Africa was probably united to South-western Asia by continuous land, along 

 which the Proboscidea reached India, and perhaps thence penetrated to North 

 America. In both these regions, as well as in Europe, the group seems to have 

 undergone the further series of modifications which gave rise to the modern type of 

 Proboscideans, 



Another consideration which adds to the importance of Africa as a centre of mam- 

 malian evolution has been pointed out by Stromer (42), namely, that part of it at 

 least has probably never been submerged since the Palaeozoic period, and formed a 

 portion of a vast Permo-Triassic land-area inhabited by a great variety of mammal-like 

 Theriodont reptiles from which the Mammalia may have actually arisen. This being 

 the case, it is not only the Tertiary, but also the Secondary, deposits of this region that 

 may be expected to yield most important data for the history of the Mammalia. 



