Many of these extinct Lemuroids so combine the characters of the Insectivora and the Ungulata (or hoofed animals), with those of their own Sub-order, that it is often extremely difficult, even impossible, sometimes, to determine to which Order they really belong, owing to a blending of characters due to their common origin. The Upper Eocene forms present many affinities with the South American Capuchin Monkeys (Cebidæ). Dr. Forsyth Major is of opinion, however, that they are more highly, and not (as is generally believed) less specialised than those now living, which appear to have been the subject of retrogressive development.
The species to be noticed below are some of the more important of those which have been ascertained to belong to the present Sub-order.
No remains assignable with certainty to the families Chiromyidæ or Tarsiidæ, have as yet been discovered. The first form to be mentioned belongs to a family which has now no living representatives.
FAMILY MEGALADAPIDÆ.
This family has recently been established by Dr. Forsyth Major, for a fossil species represented by the greater portion of a large cranium and part of its lower jaw, found in a marsh at Amboulisatra, on the south-west coast of Madagascar. This species is the only representative of the single genus of the family.
GENUS MEGALADAPIS.
Megaladapis, Forsyth Major, Phil. Trans., vol. 185 B, p. 15 (1894).
The cranium, about 10 inches long, indicates an aged animal three or four times as long as the common Cat, which is an enormous size as compared with any living Lemur. Brain-case straight, narrow, short, low, and situated at a higher level than the facial region; an enormous lateral development of the region between the eyes; orbits small in diameter, communicating freely with the temporal fossa, protruding outwards and forwards, and surrounded by a thickened ring; facial region elongate and bent upward; palate convex downwards from front to back; ridges for attachment of the temporal muscles uniting in a great central crest; frontal bones constricted behind the orbits; maxillary bones behind the molar teeth greatly inflated by air-cavities; the two halves of the lower jaw ossified together. In the upper jaw the pre-molars have one outer and one inner cusp, and the molars one internal and two external cusps, the former being deeply separated from the hind outer cusp, and joined by a ridge to the front outer cusp. In the lower jaw, the posterior pre-molar has one outer cusp, a fore and hind inner cusp (each joined by a crescent to the outer cusp), and a central inner cusp; the three molars have two outer and three alternating inner cusps, and to the outer side a basal cingulum; the posterior molar has a strongly cusped heel.
Megaladapis madagascariensis, Forsyth Major, the only species of the genus, presents many marsupial and insectivorous characters and features which show some approach towards the South-American Howlers (Alouatta), a specialisation "not in the least," according to Dr. Major, "implying a near relationship, but probably only an adaptation to a corresponding function" implied in the "vocal organs of unusual size," which, he believes, Megaladapis to have possessed. Lemurine characters, however, predominate. In the shape of its molars it is related to Lepidolemur, and still more closely to Microcebus and Chirogale, while by the characters of its inter-orbital region it approaches to the Sifakas (Propithecus) and the extinct Adapis.
The small diameter of its orbits suggests, according to Dr. Major, that in habits this extinct giant Lemur was diurnal; and from the conformation of its lower jaw "there exists," continues the same distinguished investigator, "a strong assumption that, as in Alouatta, it was provided with vocal organs of unusual size."