Online Encyclopedia

SOUTH AND CENTRAL AMERICA

Online Encyclopedia
Originally appearing in Volume V23, Page 176 of the 1911 Encyclopedia Britannica.
Spread the word: del.icio.us del.icio.us it!
SOUTH AND CENTRAL AMERICA.—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, ranging 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, Chalaroddn. 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 five 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, Xenosaurus, 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 thisfamily. 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 Sudamerikas," Zool. Jahrb., Suppl. viii., 1905), " that nearly all the principal groups of reptiles, amphibians and fishes had formerly a universal or sub-universal 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. a tg ze W w6 ~"°° `~ d . 2C 6 Chelydridae ' . o + + 0 0 0 0 0 Testudinidae 02 + + + + + + 0 Chelydidae o + 0 0 o 0 0 + Pelomedusidae o + o o + + 0 0 Trionychidae o o + + + o + o Chamaeleonidae 0 0 0 0 + + 0 0 Varanidae 0 0 0 o' + o + + Agamidae 0 0 0 + + o + + Iguanidae + + + o o + o 0 Lacertidae 0 0 0 + + o + o Zonuridae 0 0 0 0 + + 0 0 Gerrhosauridae } Anguidae + + + + +' o + o Amphisbaenidae + + +6 +4 + 0 0 0 Tejidae + + 0 0 0 0 0 0 Pygopodidae 0 0 0 0 0 0 0 + Viperinae 0 0 0 + + o + 0 Crotalinae o + + +6 0 0 + q Elapinae o + + +6 + o + + 1 Including the related Dermatemydidae and Cinosternidae. 2 With an exception. Entering, or in the borderland. ' Mediterranean countries. Rhineura; formerly wider distribution. 6 In Asia. 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 in-different 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, may have had a world-wide distribution; but Chelydidae may well have centred in an antarctic continent. Chelydridae were periarctic and have disappeared from Eurasia; N. American offshoots are the Cinosterridae and Dermatemydidae, the latter now restricted to Central American countries. Crocodilia, probably once universal, afford through the Chinese alligator an instance of the original intimate connexion of the whole holarctic region, paralleled by many other animals which now happen to be restricted to E. Asia and to eastern N. America. Lacertilia are less satisfactory for short diagnoses. America alone combines Iguanidae and Tejidae N. America: Iguanidae, Anguidae, Tejidae (and Rhineura in Florida). S. America: Iguanidae, Anguidae, Tejidae and many Amphisbaenidae. Africa and Madagascar: Chameleons and Zonuridae and Gerrhosauridae. Madagascar: Chameleons and Iguanidae. India: Varanidae, Agamidae and Lacertidae, all of which also in Africa. Australia alone has Pygopodidae. The Lacertilia are now distributed upon principles very different from those of the tortoises. According to the lizards the world is divided into an E. and a W. half. The W. alone has Iguanidae and Tejidae, the E. alone that important combination of Varanidae and Agamidae. Further subdivision is in most cases possible only by exclusion, e.g. exclusion of Lacertilia and chameleons from Australia; of Varanidae and Agamidae from Madagascar. Lizards are rather susceptible to climatic conditions, infinitely more than water tortoises. As regards Ophidia, America has Crotalinae and Elapinae, but no Viperinae. Eurasia and India alone combines Viperinae, Crotalinae and Elapinae. Africa, Viperinae and Elapinae but no Crotalinae. Australia only Elapinae. Madagascar none of these groups. The Viperinae must have had their original centre in the palaearctic countries, and they :have been debarred only from Australia and Madagascar. Both vipers 'and pit vipers are still in Asia, but true vipers are absent in America, with their fullest development now in Africa, whilst pit vipers went E., covering now the whole of America, and having developed the rattlesnakes in Sonora-land. The Elapinae are undoubtedly of Asiatic origin; they have overrun Africa, were too late for Madagascar, but early enough for Australia, where they are only poisonous snakes; and only one genus, Elaps, has got into, or rather, has differentiated in America, in the S. of which it is abundant. Opisthoglypha are useless for our purpose; they are cosmopolitan, with the exception of Australia, but probably they have one ancient centre in S. America, and another in the old world. Amblycephalidae afford another of those curious instances of apparent affinity between S.E. Asia and Central America; paralleled by Pelamis bicolor, which ranges from Madagascar to Panama, while all the other Hydrophinae belong to the Indian Ocean and the E. Asiatic seas. Aglyphous Colubrines show undoubted affinity between N. America and Eurasia; the whole group is absolutely cosmopolitan, and many of the genera, e.g. Coluber, Tropidonotus and Coronella, have proved their success by having acquired an enormous range. Snakes have comparatively few enemies, and they possess exceptional means of distribution. It is rare for a terrestrial species to have such a wide range as Crotalus terrificus, from Arizona to Argentina, or as the India cobra, which, like the tiger, is equally at home in Malay islands, Manchuria and Turkestan. The tortoises divide the habitable world into a S. and a N. world, much as do the anurous Batrachians; the lizards split it into an E. and a W. hemisphere. The poisonous' snakes, the most recent of reptiles in their full development and distribution, allow us to distinguish between Australia, America and the rest of the world. (H. F. G.)
End of Article: SOUTH AND CENTRAL AMERICA
[back]
SOUTH AMERICA
[next]
SOUTH AUSTRALIA

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click and select "copy." Paste it into a website, email, or other HTML document.