Primates.—The lowest division of the Primates, the Lemur oidia, is first recognised with certainty in rocks of Lower Eocene age in North America and Europe. These remains belong to two very distinct groups, the Lemuriformes, with a complete dentition and a comparatively elongated face, and the Tarsiiformes, in which the tooth-row is shortened, the eyes are large, the olfactory region and face very small, and the lower jaws meet in front at an acute angle. Representatives of these two groups are found in the Middle and Upper Eocene in Europe and America, and both continue in the Oligocene of Europe, but disappear at this period in North America. The two groups are then unknown in the northern hemisphere, but the Lemuriformes reappear in the Pleistocene of Madagascar in a most varied series of forms, and the Tarsiiformes are represented by the single living genus Tarsius in the East Indies. Nothing is certainly known of the remaining group of lemurs, the Lorisiformes, but it is conceivable that Pronictycebus from the Upper Eocene of France represents their ancestor.
The higher Primates fall into two completely separate divisions: the platyrrhine and catarrhine apes respectively. Of these the platyrrhines are first found in the Miocene of Patagonia, and none of them occur outside that continent. The first catarrhine is Parapithecus from the Egyptian Oligocene, a primitive form presenting distinct points of resemblance to the tarsioids. Asso ciated with this animal is Propliopithecus, which is beyond question a member of the highest family, the anthropoid apes. The earliest members of the lower families of Old World apes occur in the Lower Pliocene throughout the range of the great Pontian fauna. Their distribution presents one or two points of interest, e.g., the typical baboon is known from the Pleistocene of India, and another strange form closely allied to the living gelada has'been found in the east African Pleistocene. The giant apes have a more complete representation as fossils, a fact which is remarkable when the relative rarity of the living groups is taken into account. Pllopithecus from the Middle and Upper Pliocene of Europe appears to be essentially an ancestor of the gibbons, whilst the genus Dryopithecus has a wide distribution in Europe and Asia in the Middle Miocene and in somewhat later rocks. The closely allied Sivapithecus has been claimed as a human ancestor but really presents no definite evidence of such affinities. From Dryopithecus and its immediate allies the living giant apes certainly arose, and such evidence as exists is con sonant with the view that man also came from the same stock.
The outline of the history of land-mammals contained in the preceding pages shows that the present distribution of a mammal may tell us nothing whatsoever about the place of its origin, or the time at which it came into its existing habitat. All the great
land-masses of the world except Australia and Madagascar have been continuous with one another at some time during the Tertiary period and representatives of all the higher orders have been enabled to cross the bridges between them. The fact that each continent none the less has a distinctive fauna, is due to the extinction which has overtaken the members of every group in some portions of its former range, the differences in the period at which the union of the continents took place, and the peculiari ties in the geographical conditions of the bridges which made them available to certain forms whilst they could not be crossed by others. The geographical conditions which may act as barriers to the free migration of mammals are very varied. A wide strait of sea cannot be crossed by most mammals but there is evidence that certain creatures have in fact reached islands by some rare and casual mode of distribution not available to most forms.
Madagascar.—Perhaps the best evidence of the possibility of such transference is afforded by Madagascar. Taking the Pleisto cene and recent faunas of that island together, we find that it is inhabited by very many genera of lemurif orm lemurs, varying in size from animals no bigger than a squirrel to a form with a skull more than a foot in length. Although all the living and the majority of the extinct forms are strictly arboreal some of the larger lemurs were terrestrial and even perhaps aquatic in their habits. There is however no doubt that all these forms despite their very varied appearances are extremely closely related and that they may all have arisen from a form resembling Lemur itself.
The only other important element in the Madagascan fauna is the group of many genera included in the zalambdodont insecti vores. All these belong to the single family Centetidae and may have arisen from a single form. The carnivores are represented by a few genera of Viverridae, all extremely peculiar in their structure ; the largest and most interesting is the fossa, an animal whose true relationships are obscure. There is another viverrid, Eupleres, with very small widely-separated teeth like those of an insectivore, and finally there is a much more typical viverrid, perhaps belonging to Viverrus itself. The rodents are included in the single family Nesomyidae, peculiar to the island. The only other forms are bats, including the fruit-bat Pteropus not found in Africa, a pig of the genus Potamochoerus and a pigmy hippo potamus now extinct.