The Geographical Distribution of Animals, Volume 1 / With a study of the relations of living and extinct faunas as elucidating the past changes of the Earth's surface

by Alfred Russel Wallace

This may be defined as the equatorial-forest sub-region, since it comprises all that portion of Africa, from the west coast inland, over which the great equatorial forests prevail more or less uninterruptedly. These commence to the south of the Gambia River, and extend eastwards in a line roughly parallel to the southern margin of the great desert, as far as the sources of the upper Nile and the mountains forming the western boundary of the basin of the great lakes; and southward to that high but marshy forest-country in which Livingstone was travelling at the time of his death. Its southern limits are undetermined, but are probably somewhere about the parallel of 11° S. Latitude.[^[10]]

This extensive and luxuriant district has only been explored zoologically in the neighbourhood of the West coast. Much, no doubt, remains to be done in the interior, yet its main features are sufficiently well known, and most of its characteristic types of animal life have, no doubt, been discovered.

Mammalia.—Several very important groups of mammals are peculiar to this sub-region. Most prominent are the great anthropoid apes—the gorilla and the chimpanzee—forming the genus Troglodytes; and monkeys of the genera Myiopithecus and Cercocebus. Two remarkable forms of lemurs, Perodicticus and Arctocebus, are also peculiar to West Africa. Among the Insectivora is Potamogale, a semi-aquatic animal, forming a distinct family; and three peculiar genera of civets (Viverridæ) have been described. Hyomoschus, a small, deer-like animal, belongs to the Tragulidæ, or chevrotains, a family otherwise confined to the Oriental region; and in the squirrel family is a curious genus, Anomalurus, which resembles the flying squirrels of other parts of the world, without being directly allied to them.

Birds.—In this class we find a larger proportionate number of peculiar forms. Hypergerus and Alethe, belonging to the Timaliidæ, or babblers, are perhaps allied to Malayan groups; Parinia, a peculiar form of tit, is found only in Prince's Island; Ixonotus is an abundant and characteristic form of Pycnonotidæ; Fraseria, Hypodes, Cuphopterus, and Chaunonotus, are peculiar genera of shrikes; Picathartes is one of the many strange forms of the crow family; Cinnyricinclus is a peculiar genus of sun-birds; Pholidornis is supposed to belong to the Oriental Dicæidæ, or flower-peckers; Waldenia is a recently-described new form of swallow; Ligurnus, a finch, Spermospiga, a weaver bird, and Onychognathus a starling, are also peculiar West African genera. Coming to the Picariæ we have Verreauxia, a peculiar woodpecker; three peculiar genera of barbets (Megalæmidæ); the typical plantain-eaters (Musophaga); Myioceyx, a peculiar genus of kingfishers; while Berenicornis is a genus of crested hornbills, only found elsewhere in Malaya. The grey parrots, of the genus Psittacus, are confined to this sub-region, as are two peculiar genera of partridges, and three of guinea-fowl. We have also here a species of Pitta, one of the Oriental family of ground-thrushes; and the Oriental paroquets, Palæornis, are found here as well as in Abyssinia and the Mascarene Islands.

We thus find, both in the Mammalia and birds of West Africa, a special Oriental or even Malayan element not present in the other parts of tropical Africa, although appearing again in Madagascar. In the Mammalia it is represented by the anthropoid apes; by Colobus allied to Semnopithecus, and by Cercocebus allied to Macacus; and especially by a form of the Malayan family of chevrotains (Tragulidæ). The Malayan genus of otters, Aonyx, is also said to occur in West and South Africa. In birds we have special Oriental and Malayan affinities in Alethe, Pholidornis, Berenicornis, Pitta, and Palæornis; while the Oriental genus Treron has a wide range in Africa. We shall endeavour to ascertain the meaning of this special relation at a subsequent stage of our inquiries.

Plate V.—River Scene in West Africa, with Characteristic Animals.—Our artist has here well represented the luxuriance and beauty of a tropical forest; and the whole scene is such as might be witnessed on the banks of one of the rivers of equatorial West Africa. On the right we see a red river-hog (Potamochœrus penicillatus), one of the handsomest of the swine family, and highly characteristic of the West African sub-region. In a tree overhead is the potto (Perodicticus potto), one of the curious forms of lemur confined to West Africa. On the left is the remarkable Potamogale velox, first discovered by Du Chaillu,—an Insectivorous animal, with the form and habits of an otter. On the other side of the river are seen a pair of gorillas (Troglodytes gorilla), the largest of the anthropoid apes.

The bird on the wing is the Whydah finch (Vidua paradisea), remarkable for the enormous plumes with which the tail of the male bird is decorated during the breeding season. The crested bird overhead is one of the beautiful green touracos (Turacus macrorhynchus), belonging to the Musophagidæ, or plantain-eaters, a family wholly African, and most abundant in the western sub-region.

Reptiles.—In this class we find a large number of peculiar forms; 13 genera of snakes, 3 of lizards, and 2 of tortoises being confined to the sub-region. The snakes are Pariaspis, Elapops, and Prosymna (Calamariidæ), Rhamnophis, Herpetethiops, and Grayia (Colubridæ), Neusterophis and Limnophis (Homalopsidæ), Simocephalus and Holurophis (Lycodontidæ); Pelophilus (Pythonidæ); Elapsoidea (Elapidæ); and Atheris (Viperidæ). The lizards are Dalophia (Lepidosternidæ); Otosaurus (Scincidæ); Psilodactylus (Geckotidæ). The tortoises, Cinyxis (Testudinidæ) and Tetrathyra (Trionichidæ).

Amphibia.—Of Amphibia, there are 2 peculiar genera of tree-frogs, Hylambatis and Hemimantis, belonging to the Polypedatidæ.

Plate V.