Page:EB1911 - Volume 23.djvu/192

DISTRIBUTION] Amphisbaenidae Amphisbaena itself occurs in Puerto Rico and on the Virgin Islands. Of Tejidae only Ameiva, not Cnemidophorus. Snakes: a Typhlops in Puerto Rico; of boas Epicrates, Ungalia and Corallus, the latter re-occurring in Madagascar. Absent are: Viperidae, Elapinae and Opisthoglyphs; of aglyphous colubrines the Central American genera Urotheca, Dromicus, Drymobius and Leptophis; the genera of distinctly northern origin.

.—The fauna is very rich. It is advisable first to mention those groups which are either confined to Central America (including the hot lowlands of Mexico), e.g. the Dermatemydidae, Eublepharinae, Anelytropsis and the aglyphous colubrines: Urotheca, Dromicus, Drymobius, Leptophis, Rhadinea, Streptophorus, or which, from their N. centre have sent some genera into Central America, or beyond into the S. continent: e.g Chelydra rossignoni, rangin from Guatemala to Ecuador; one Cinosternum extending into Guiana; Testudo tabulata, the only terrestrial tortoise of S. America, besides the gigantic creatures of the Galapagos Islands; a few Eublepharinae reaching Ecuador; of Anguidae Gerrhonotus coeruleus, extending S. to Costa Rica; of Scincidae, Mabuia and Lygosoma, which extend far into S. America, and the same applies to the Amphisbaenidae. Immigrants from the N. are probably also the Iguanidae, although they have found a congenial home in the S. countries, where they are now represented by an abundance of genera and species, e.g. Laemanctus and Corythophanes of Mexico, Anolis, Iguana, Basiliscus, Ctenosaura, Polychrus, Hoplurus, Chalarodon. Amongst snakes the following appear to be of N. origin: Boidae (with the Pythonine Loxocaemus bicolor in Mexico), in spite of their great development of boas and anacondas in the S.; certainly Crotalinae, of which only one species, C. terrificus, is found in S. America; further, some aglyphous colubrines, which have sent a few species only into Central, and still fewer into S. America,* e.g Tropidonotus, Ischnognathus, Contia,* Ficimia, Coluber, Spilotes, Pityophis, Coronella* and Zamenis.

After these numerous restrictions we should expect the genuine autochthonous fauna of the S. American continent to be very scanty, especially if we remember those important Old World groups which are absent in America, e.g. Varanidae, Lacertidae, Agamidae and chameleons, and that Central and S. America have no Trionychidae. The oldest S. American reptilian fauna is composed as follows. It is the only part of the world which possesses Chelydidae in abundance, e.g. of Chelys the Matamata, Hydromedusa, and of Pelomedusidae, Podocnemis, which re-occurs in Madagascar. Crocodilia are represented by Crocodilus americanus and C. moreleti in the N. and by about live species of Caiman. Of Lacertilia geckos are rather few, mostly in the N.W. of the continent, more numerous in Central America and the Antilles. The Tejidae are clearly a neotropical family, with several dozen genera in S. America; of all these, only Ameiva and the closely allied Cnemidophorus extend through and beyond Central America: Ameiva into the E. and W. hot lands of Mexico and into the Antilles, Cnemidophorus through Mexico far into most of the United States with a few species. Of snakes there is an abundance. Typhlopidae and Glauconiidae are well represented. Of aglyphous colubrines many genera, some of these extending northwards into Mexico, but not to the Antilles, e.g. Atractes, Tropidodipsas, Dirosema, Geophis, Xenodon.

Opisthoglypha are very numerous in genera and species both in S. and Central America, whence many of the arboreal forms extend into the hot countries of Mexico, while a few terrestrials have spread over the plateau and thence into the United States, none entering the Antilles; such typical neotropical genera are Himantodes, Leptodira, Oxyrhopus, Erythrolamprus, Conophis, Scolecophis, Homalocranium, Petalognathus, Leptognathus. Most of the Amblycephalidae are neotropical, the others in S E. Asia. Of Elapinae only the genus Elaps occurs, but with many species. Of the Crotalinae, Lachesis is the essentially neotropical genus, with many species, some of which enter the hot lands of Mexico, e.g. L. lansbergi s. lanceolatus, a very widely distributed species, the only pit viper which has entered the Lower Antilles.

The above survey of the world shows that but very few of the principal families of reptiles are peculiar to only one of the main “regions.” The occurrence of some freak, constituting a little family or sub-family by itself in some small district, and therefore put down as peculiar to a whole wide region, cannot be much of a criterion, e.g. Rhachiodon, Elachistodon, Acrochordinae, Uroplates, Xenasaurus, Heloderma, Aniellidae, Dibamus, Anelytropidae, Platysternum. They are not characteristic of large countries, but rather local freaks. Quite a number of very ancient families have such a wide distribution that they also are of little critical value, notably the peropodous snakes, which have survivors in almost any tropical country; such cosmopolitans are also geckos and skinks.

A difficulty which is ever present in such zoogeographical investigations is the uncertainty as to whether our zoological families and sub-families and even genera are genuine units, or heterogeneous compounds, as for instance the Anelytropidae, of which degraded skinks there is one in Mexico, two others in W. Africa. Heloderma in Mexico and Lanthanotus in Borneo are both without much doubt descendants of some Anguid stock, but when we now combine them, in deference to our highest authority, as one family, we thereby raise the tremendous problem of the present distribution of this

family. Boas and pythons are likewise not above suspicion, cf. some boas in Madagascar and the python Loxocaemus in Mexico. The opisthoglyphous colubrines are almost certainly not a natural group, not to speak of numerous genera of the aglyphous assembly. To avoid arguing in a circle, such doubtful units had better be avoided whilst building hypotheses.

G. Pfeffer has recently endeavoured to show by an elaborate careful paper (“Zoogeographische Beziehungen Südamerikas,” Zool. Jahrb., Suppl. viii., 1905), “that nearly all the principal groups of reptiles, amphibians and fishes had formerly a universal or subuniversal distribution, and that therefore it is not necessary to assume a direct land connexion of S. America with either Africa or Australia, with or without an Antarctic.” Many cases of such a former universal distribution are undoubtedly true, but the question remains how the respective creatures managed to attain it.

For true characterization of large areas we must resort to the combination of some of the large wide-ranging families, and equally important is the absence of certain large groups; both to be selected from the following table.

Deductions from this table show, for instance, that Australia is quite sufficiently characterized by the possession of Chelydidae and Varanidae; Madagascar by the presence of chameleons and Pelomedusidae. On the other hand, the separation of the whole of Africa from Asia, or the diagnosis of the palaearctic “region,” would require the combination of several positive and negative characters. Chelonians are very diagnostic, expressed by the following combinations of families:—

America as a whole: Chelydridae and Cinosterridae and Dermatemydidae.

N. America: Chelydridae and Trionychidae, but only E. of the Rockies.

S. America: Chelydidae and Pelomedusidae.

Africa: Trionychidae and Pelomedusidae.

Madagascar: Pelomedusidae and Testudinidae.

India and Eurasia: Trionychidae and Testudinidae.

Australia: Chelydidae only.

That the Chelonians are regionally so very diagnostic that their main families are still in rational agreement with the main divisions of land, is perhaps due, first, to their being an ancient group; secondly, to their limited means of distribution (none across the seas, omitting of course Cheloniidae, &c.); and lastly, to their being rather indifferent to climate. Note, for instance, Trionyx ferox from the Canadian lakes to the Gulf of Mexico, Cinosternum pennsylvanicum from New York to New Orleans. It may be taken for certain that wherever a Testudo occurs as a genuine native, it has got there by land, be the locality the Galapagos, Aldabra, Madagascar or some Malay islands. The Trionychidae reveal themselves as of periarctic origin, being debarred from Australia, Madagascar and the neotropical region (alleged from Eocene Patagonia). Testudinidae are cosmopolitan, excluding Australia, and practically also the Antilles; and Testudo is most instructive with its almost similar distribution; but something has gone wrong with this genus in America, where it flourished in mid-Tertiary times.

Pleurodira are less satisfactory than they appear to be from a merely statistical point of view. The Pelomedusidae, being known from European Trias and from nearctic cretaceous formations,