We shall now ask the reader to conceive a primitive placental mammal type, and to consider briefly the relationships of the various groups that have sprung from it. The group whose evolution has been perhaps least progressive is that of the Edentates, including the sloths, armadillos, and American ant-eaters (Fig. 114). Then, on the one hand, we have the herbivorous types, including the remarkable sea-cows (Fig. 115), the rodents (Fig. 116), and the hoofed animals, leading up from such comparatively primitive forms as the coneys (Fig. 117) to such highly specialised types as the giraffe (Fig. 118). The other series of groups are believed to be more nearly related to each other than to the aforementioned, and the nearest approach to their common ancestor, among modern mammals, is probably to be found in the Insectivora (Figs. 119 and 120). Differing sharply from the Insectivora in their possession of wings, but otherwise closely similar, are the bats (Fig. 121). From this same insectivor-like type have probably evolved the whales (Fig. 122), the seals, etc. (Fig. 123), the carnivora (Fig. 124), and finally the primates, leading up through the lemurs to the monkeys and man. Thus merely indicating the many and devious roads of mammalian Evolution, we turn again to the one particular line that we set out to follow.
Fig. 116.—Porcupine.
Fig. 117.—Coney (Hyrax).
Fig. 118.—Giraffe.
Photo by Sport General.
Fig. 119.—Centetes ecaudatus, a primitive insectivor.