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Investigations of the Ichthyofauna of Nicaraguan Lakes Papers in the Biological Sciences

1976

Derivation of the Freshwater Fish Fauna of Central America

George S. Myers California Academy of Sciences

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Myers, George S., "Derivation of the Freshwater Fish Fauna of Central America" (1976). Investigations of the Ichthyofauna of Nicaraguan Lakes. 9. https://digitalcommons.unl.edu/ichthynicar/9

This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Investigations of the Ichthyofauna of Nicaraguan Lakes by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Side looking radar mosaic of research area taken from aircraft at about 40,000 feet. Lake Managua at upper left; Lake Nicaragua with Rio San Juan emptying at lower right. Data acquisition by Westinghouse. Courtesy Instituto Geografico Nacional de Nicaragua. Published in INVESTIGATIONS OF THE ICHTHYOFAUNA OF NICARAGUAN LAKES, ed. Thomas B. Thorson (University of Nebraska-Lincoln, 1976). Copyright © 1976 School of Life Sciences, University of Nebraska-Lincoln.

Made in United States of America Reprinted from COPEIA, 1966, No.4, December 23 pp. 766--773

Derivation of the Freshwater Fish Fauna of Central America

GEORGE S. MYERS

The nature, composition, and evolution of Centra) American freshwater fish groups are discussed in relation to the history and derivation of the faunal elements. It is concluded that the entire area between the Isthmus of Tehuantepec and eastern Panama was and always had been devoid of primary (obligatory) freshwater fishes prior to the very late Tertiary. Instead, secondary freshwater fishes evolved in this area during the Neogene and perhaps for a longer period, the Poeciliidae having probably had a longer history within the area than the Cichlidae. In the late Tertiary a very few North American immigrants entered the area from the north, and towards the end of the Pliocene the closing of the very ancient Panama sea gap permitted an influx of South American primary types. Most of these have not yet gotten past Costa Rica, but a few aggres­ sive characids have reached Guatemala or southern Mexico and one has reached Texas. It follows that the rich South American primary fresh­ water fish fauna could not have been originally derived from or through Central or North America, and continental drift (not here discussed in detail) is suggested to explain South American-African similarities.

y purpose in this paper is to outline, in for they not only combine a considerable Ma very general way, what the present time span into one map, but also are based distribution and character of the freshwater upon correlations which later work often fishes of Central America south of the Isth­ shows to have been inexact. Finally, biogeo­ mus of Tehuantepec appear to demonstrate graphical conclusions are often in part based in regard to their geographical derivation as upon geological conclusions, and are then they evolved and dispersed. It is common in again cited by geologists as evidence, produc­ studies of this kind to examine the geological ing circular reasoning of no mean sort. I evidence in some detail and to attempt to have tried to let the fishes tell their story, correlate the paleogeographical findings of within only the most general of geological geologists with the present distributional pic­ and geographical limits. There are two gen­ ture of the organisms concerned. So far as possible, I have not done so. Perhaps as eral books on the geology of the region much time has been wasted in attempting to (Schuchert, 1935; and Weyl, 1961), and these make dispersional patterns of plant and ani­ summarize most of the important points. mal groups fit paleogeographical maps pub­ lished by geologists as biogeographers have COMPOSITION OF THE FISH FAUNA wasted in drawing imaginary land-bridges Dr. R. R. Miller (1966) has compiled a with no geological evidence to back them. list of the fishes known from fresh water be­ Central America is not as well known, geo­ tween the Isthmus of Tehuantepec and the logically, as North America. Moreover, pa­ Colombian border of Panama. In my totals, leogeographical maps are rarely very exact, I have added a very few still undescribed

117 MYERS-CENTRAL AMERICAN FISH FAUNA 767

forms which I know to have been collected 1). This is somewhat inexact, for several spe­ by Professor Rivas and Dr. Rosen. With cies are found in Costa Rica and also north­ these additions, I find a total of 446 species ward into Nicaragua or beyond. known to me from the area. Of these, 104 Returning to the primary fishes, it is nota­ are primary freshwater fishes, 165 are secon­ ble that all of them are ostariophysans­ dary species, and 187 are peripheral forms. characoids, gymnotoids, cyprinoids, and cat­ Of the peripheral species, a good many are fishes. This also is a remarkable fact. In all what I would call sporadic, that is, which other large continental areas in which os­ enter fresh water from the sea in river tariophysans form a sizable part of the fresh­ mouths, or occasionally even spend much water fish fauna, they are accompanied by at time away from the sea. Among these are the least a few other types of primary (obliga­ tarpon and the bull shark. These peripheral tory) freshwater fishes, such as the sunfishes freshwater fishes do not concern us at the and true perches in North America. moment. I wish first to consider the core of The most startling fact of all is the ex­ the freshwater fauna, the primary forms, most treme poverty, in primary freshwater fishes, or all of which cannot survive long in sea of what may be called middle Central Amer­ water of normal salinity. ica-the area between Costa Rica and Te­ The 104 species of primary freshwater spe­ huantepec. In no other reasonably extensive cies belong to 18 families, the largest of continental area on earth where cypriniform which (in our area) is the Characidae, with fishes occur naturally are they (and other 42 species. Second is the catfish family Pime­ primary freshwater fishes) so few in species lodidae with 23 species, and third is the cat­ and so greatly outnumbered by the species of fish family Loricariidae, with 14 species. the secondary and even of the peripheral Other families are: Catostomidae (2 species) , group. The freshwater fish fauna of middle Erythrinidae (2), Gasteropelecidae (1), Paro­ Central America is without parallel in this dontidae (2), Ctenoluciidae (1), Curimatidae regard. (1), Lebiasinidae (2), Gymnotidae (2), Ap­ Indeed, one might call this great region, teronotidae (4), Ictaluridae (1), Auchenipteri­ from Tehuantepec to the Costa Rican tribu­ dae (1), Ageneiosidae (1), Trichomycteridae taries of Lake Nicaragua, an area of vacuum, (2), Callichthyidae (1), and Astroblepidae (1). or near-vacuum, of primary freshwater fish However, such totals are misleading if one stocks (Myers, 1963:20). I believe the anom­ does not consider the areas inhabited by the aly to be rather simply explainable, but this fishes. Of the 18 families and 104 species of simple explanation has far-reaching conse­ primary freshwater fishes, two-thirds of the quences. Not only does it deeply affect the families (12) and nearly three-fourths of the theories of Darlington (1957) on continental species (74) are found only in Costa Rica relationships and fish dispersal, but also it and Panama-that small and narrow part of deeply affects the conclusions of the only Central America adjacent to South America. modern ichthyologist who has attempted to Northwards, from the Costa Rican-Nicara­ utilize the theory of continental drift to ex­ guan border to the Isthmus of Tehuantepec, plain freshwater fish dispersal (Kosswig, only 5 families and 27 species of primary 1944). However, in order to give my explana­ freshwater fishes are known! This is a re­ tion, I must make a few observations on markable fact. ostariophysan ecology and evolution. Among the 165 secondary freshwater fishes, which have some tolerance for normal sea OSTARIOPHYSAN ECOLOGY AND EVOLUTION water, no such concentration of the majority vVhat I have to say on these subjects is of the species in the south is noticeable. The very brief, for I am presenting the subject in more northerly areas are much larger and, more detail elsewhere. First, I wish to point as would be expected, have more species. In out some facts of characoid and cyprinoid listing the number of species following each ecology and evolution that I believe will be family, I give first the total number of spe­ accepted because most ichthyologists know cies known for the entire area, followed by them, even though they have rarely or never the number found only north of Costa Rica: been stated. Lepisosteidae (1-1), Cyprinodontidae (25- The characoids (Characidae and their close 18), Poeciliidae (56-about 34), Anablepidae relatives) and the cyprinoids (Cyprinidae and (1-1), Cichlidae (83-71), Synbranchidae (2- their close relatives) have a generally com-

118 768 COPEIA, 1966, NO.4 plementary distribution, except in Africa. the African lakes and in Central America, where both occur. Together, they form the including many predatory species in each, order Cypriniformes (see Greenwood, Rosen, cuts down the evolutionary rate of smaller vVeitzman, and Myers, 1966), which, together cypriniform fishes. This is a demonstrably with the catfish order Siluriformes, comprises impossible explanation. The rivers of both the superorder Ostariophysi. Wherever they South America and Africa are rich in genera occur naturally in any numbers, save in Cen­ and species of cichlids, many of them highly tral America and certain endemic lake faunas, predatory, but the number of species of cypriniform fishes have become more speciose cypriniform fishes in the same rivers is far than other groups, especially in the smaller greater. Only in lakes, to which cichlids are species. Everywhere in fresh waters, except much better adapted than are cypriniforms, in Australia, species of little cyprinoids or can such a theory perhaps be considered to characoids are the principal forage fishes on have applicability. Other explanations, in­ which larger predators feed. They swarm in volving periodic destruction of the fish fauna the lowland rivers and in the highland by the admittedly high incidence of vulcan­ brooks. \Vherever larger predators belonging ism in Central America, or periodic marine to other orders are few or absent, and oc­ transgressions of large extent, cannot be en­ casionally when they are fairly numerous, the tertained, because such catastrophes would cypriniform fishes themselves have evolved also have involved the far more speciose large and important predatory forms (Sa 1- cichlids and poeciliids in the same areas. minus, Brycon, and Serrasalmus in South The only acceptable explanation is that America; Hydrocynus and large Barilius in already suggested by myself (Myers, 1938)­ Africa; Elopichthys and Luciobrama in the cypriniform fishes in middle Central China; Ptychocheilus in western North Amer­ America are, geologically speaking, very new ica). They are the most successful, aggres­ to the area. They have not yet had time to sive, numerous and all-pervading of fresh­ evolve many endemic species or genera. And water fishes. Cyprinidae have probably been they have penetrated into the area far more present in North America only since the recently than the more speciose Central Early Miocene (Myers, 1938), but they now American Poeciliidae and Cichlidae. form the preponderant element of the fauna. One can make such a statement purely on In Africa, where Cyprinidae entered (prob­ the basis of the literature, but seeing the ably in the Miocene or Pliocene) a continent fauna in the field is even more convincing. already inhabited by the other large cyprini­ Four years ago I collected in the basin of form group, the characoids, the cyprinids Lake Nicaragua, Lake Managua, and the Rio have become the more numerous group, in San Juan. The rotenone rarely or never species and in individuals'! But they by no brought up more than four species (usually means swamped-out the older African chara­ only two or three) of cypriniform fishes at coids, numbers of which, both large and anyone place-a couple of small characids small, still survive. Even in the remarkably (usually a Roeboides, an Astyanax and a rich endemic African lake faunas, composed large predatory Brycon, up to nearly a yard mostly of the highly preadapted Cichlidae, in length)-mixed with a much more varied small cypriniform fishes (e.g., Engraulicypris) assortment of Cichlidae, a gymnotus, a Rham­ tend to form the bulk of the primary forage dia, some poeciliids, and some gobies. Gar­ fishes. pike were present; also tarpon and sharks. Why are the species of Cypriniformes so But it was clear that at least 50% of the few in middle Central America? Several ex­ biomass or weight of fish present in the planations occur. One is that a large fauna streams must have been composed of the of cichlid species, which is present equally in three or four species of Characidae! This was certainly true if one adds to the characids 1 The relative newness of Cyprinidae in Africa is the biomass of pimelodid catfishes present­ demonstrated beyond reasonable doubt by the small usually a single species of Rhamdia. In other number of African genera, nearly all of which are identical with dominant genera of the far richer and words, the few species of newcomers, both more diverse cyprinid fauna of Asia. In other words, characids and Rhamdia, are today by far the as in any intercontinental, filter-bridge invasion, it was almost entirely the common, dominant Asiatic genera most numerous fishes in the streams. These which colonized Africa. Also, there can be no doubt ostariophysans are obviously in the early in this instance that the transfer was a one-way affair, for none of the older African groups reached Asia. stages of taking over an area newly opened

119 MYERS-CENTRAL AMERICAN FISH FAUNA 769

to them. No other explanation appears to whole, less able to make use of swift water be possible. streams than the six genera mentioned above, while some have a rather highly specialized DERIVATIO~ OF THE FAUNAL ELEMENTS ecology. Aside from peripheral groups, the only If one includes all of ~Iexico as well as families of either primary or secondary fresh­ Central America, there are nearly a hundred water fishes present in middle Central Amer­ species of Cichlidae in the area, and the ica that were unquestionably derived from group has obviously had a special center of North America are the garpike (Lepisostei­ evolution in this region. However, South dae), with one species extending as far south America has more cichlid species and far as the Costa Rican tributaries of Lake Nica­ more genera. Nearly all the endemic Central ragua; the suckers (Catostomidae), with two American forms belong to the common species reaching southern Mexico and Guate­ South American genus Cichlasoma. There mala; and the North American catfish (Icta­ can be little doubt that this element of the luridae), with one species extending from fauna arrived in Central America relatively southern Mexico into Guatemala and British recently, but probably prior to the im'asion Honduras. The derivation of these is un­ of the Characidae. In the ostariophysan questioned; they came from the north. So, vacuum of middle Central America, before perhaps, did the Cyprinodontidae and Poe­ the advent of characids, relatively rapid evo­ ciliidae. lution of Cichlasoma species obviously went At the southern end, the relatively rich on, both in streams and in lakes. Panamanian fauna of primary fishes is all Less numerous in species, but more diverse South American. Many species are identical in Central American genera than the cichlids, with those of the Rio Atrato and even the the Poeciliidae would appear to have had a Rio Magdalena in Colombia, but, as would longer period for evolution in the region be expected, even the apparently rich Pana­ than the Cichlidae. Apparently limited to manian fauna is merely a pale reflection of rather small physical size by heredity, the the greater richness of the South American poeciliids nevertheless evolved such a rapa­ rivers. cious predator as Belonesox in middle Cen­ Leaving aside the Panama-Costa Rica tral America, as well as mud-eaters, surface­ fauna at the south, the few North Ameri­ film feeders, alga-scrapers, and insectivorous can elements, and, for the moment, the forms. The entire gambusine group, as well Cyprinodonts, Cichlidae, and marine deriva­ as Pseudoxiphophorus, tends to be predaceous tives, there seems to be no doubt that all the on fishes smaller than themselves, including rest of the faunal elements of middle Central the young of larger species. I doubt that America came from the south-evidently from poeciliid forms of such diverse specialization South America. Astyanax, Hyphessobrycon, would have been evolved had there been Roeboides, Brycon, Gymnotus, and Rhamdia much competition from other families. are all generalized, widespread genera in Parenthetically, I find it somewhat diffi­ cult to talk about certain generic evolution­ South America. They are precisely the types ary and geographic trends according to the that would be expected to be in the fore­ new classification of Rosen and Bailey (1963). front of any invasion of newly opened terri­ For example, all or nearly all species of the tory, because they (and relatively few others) old (and more restricted) genera Poecilia, have developed South American ranges al­ M ollienesia, Limia, and Xiphophorus appear most or quite coextensive with the ranges of to be averse to soft, acid water, and to need the families or subfamilies to which they be­ some dissolved calcium carbonate or chloride, long. They found no climatic barriers in while Lebistes, Micropoecilia, Pamphorich­ their invasion of the wholly tropical area of thys, and Pseudopoecilia tend to inhabit soft, middle Central America, a type of barrier acid water by preference. In general, poe­ which undoubtedly acted as a deterrent to ciliids appear to be few in species and in in­ most North American groups moving south­ dividuals in the great soft water areas of ward. The South American genera which Guiana and Amazonia, although this may have gotten no farther north than Panama or be related to the diversity and numbers of Costa Rica, although also mostly members of characoid fishes in such areas. However both relatively widespread genera, are, on the soft water and characoid predominance have

120 770 COPEIA, 1966, NO. 4

probably persisted in the Guiana-Amazon tween Bramocharax and Astyanax (collected region for the entire Cenozoic, and if the by Rivas). The teeth and mouth structure of poeciliids had a South American origin, one Bramocharax give evidence of derivation or the other or both of these must have con­ from Astyanax, perhaps not too long ago, stituted limiting factors to their northward and discovery of the new intermediate genus dispersal. However, now that a close ally or lends strong support to the origin of Bramo­ member of the Cnesterodontini has been charax from the earliest Astyanax invaders. found in Guatemala by Rosen, all of the Rhamdia, perhaps the most ubiquitous and main generic groups except the Guianan ecologically generalized South American cat­ Tomeurinae are known from middle Central fish genus, undoubtedly arrived concurrently America, and it seems reasonable to conclude with the characids. Invasions by primary that this area has formed the main evolu­ freshwater fishes of !\orth America type were tionary center of the group. confined to two species of the catostomid One more possible factor in regard to poe­ genus I ctiobus and one species of the catfish ciliid evolution needs to be mentioned. If genus lctalurus, and these have barely the poeciliids were present and evolving in reached the northern part of middle Central middle Central America prior to the advent America. Considering what we know of the of South American cichlids and ostariophy­ rates of ostariophysan evolution, it would sans, invasion by these often larger and more appear highly probable that the entire area powerful newcomers might have tended to of middle Central America constituted a cut down the species numbers and diversity region of primary ostariophysan vacuum un­ of the small, weak-swimming poeciliids. At til the Late (and possibly very late) Tertiary. least some special ecological niches or bio­ In a continental area of such extent, it is to topes formerly occupied by poeciliids, but for the highest degree improbable that Early which the newcomers were better adapted, Tertiary primary ostariophysans were present would have been rapidly filled by the in­ in middle Central America, only to be wiped vaders, with concurrent disappearance of out by vulcanism or marine transgressions. such poeciliids. I suspect that this has hap­ 2. It follows that middle Central Amer­ pened in our area, perhaps to some larger, ica, and probably also Costa Rica and Pan­ stream-inhabiting poeciliids, leaving the many ama, must have been protected from invasion smaller poeciliids, as in North and South by primary freshwater fishes from the north America, only in what might be termed pe­ and south for a very long period of geological ripheral habitats. time. Highly effective barriers to invasion must have been present to the south and THE PICTURE OF FISH EVOLUTION probably in the north, and these barriers AND DISPERSAL were almost certainly of a geographical The picture that emerges so strongly from (geological) character in the south. The careful evaluation of the elements and nature climatic factor of the beginning of tropical of the freshwater fish fauna of middle Cen­ climates just north of Tehuantepec has un­ tral America may be summarized as follows: doubtedly played a role in the north, in I. Ostariophysan fishes of the primary practically excluding dominant North Amer­ freshwater type are relatively new to the area ican cyprinoids from the area to the present and were never present there previous to the day. A climatic factor would not have been beginnings of the invasions which we now see operative at the southern barrier. The fishes, in progress. There are no ancient relicts of of the fossils of which we know next to noth­ this group present. If primary cypriniform ing, do not date the breakdown of the south­ fishes had been present at any previous time, ern barrier to primary freshwater fishes. All especially in the earlier Tertiary, pockets or the fish evidence alone can do is to indicate remnants discordant with the members of the that the breakdown in the south was almost late invasion by dominant South American certainly of Late Tertiary age. genera would almost surely have remained. 3. Before the breakdown of the southern The only endemic genera of Characidae pres­ barrier, the Central American fish fauna ent are Bramocharax (two species in Nicara­ lacked all elements of a primary freshwater gua and one still to be described from Guate­ fish fauna, except perhaps for two or three mala) and a localized and, so far, unde­ northerly forms in the north. It was com­ scribed genus more or less intermediate be- posed of peripheral invaders from the sea

121 ~IYERS-CENTRAL AMERICAN FISH FAUNA 771

(gobies, centropomids, clupeids, atherinids, Schuchert, 1935; Weyl, 1961; Patterson and etc.) and of two widely different groups of Pascual, 1963). secondary freshwater fishes-cichlids and It appears that a sizable core of middle cyprinodonts, which are known to be able Central America, comprising Honduras, EI occasionally to use the sea for dispersal, Salvador, and large adjacent parts of Guate­ either across open sea barriers or along coasts. mala and Nicaragua, has remained unflooded EYen today these elements are more numer­ by the sea since the Paleozoic. However, even ous than the primary fishes in number if this area did not emerge until the earlier of species. Evidence from the diversity of Neogene, the picture of fish distribution the fishes themselves strongly indicates that would not be changed in any important way, the cyprinodonts, especially the poeciliids, for certainly some sizable sections of middle were there and evolving for a considerable Central America must have been emergent period before the arrival of cichlids, and the at any particular time. To the northward, invasion of the latter almost certainly pre­ especially in the Tehuantepec region, there ceded that of the primary ostariophysans, was considerable marine transgression during which are now finally beginning to over­ the Cenozoic, which kept the Yucatan penin­ whelm the cyprinodont and cichlid diversity sula under water during most of that time. into which they were injected. By conti­ In general, the Isthmus of Tehuantepec was nental standards, the fauna is still a highly usually much narrower than at present, and unbalanced one. Cichlid morphological con­ there was Atlantic-Pacific sea connection formity to the Cichlasoma pattern in Central across it during the Miocene and Pliocene, America is strong evidence that the Central and perhaps at earlier times. Also, there was American cichlids originated in South Amer­ oceanic connection across southern Nicara­ ica and that the subsequent evolution of gua during the Oligocene and Miocene, and Cichlasoma and its close relatives in the perhaps at other times. Central American ostariophysan vacuum has If the Panama interocean passage was ever been rapid and geologically of no very great bridged by dry land previous to the Pliocene, age. Our principal fossil evidence consists that bridging was far back in the Mesozoic. of a single Miocene cichlid from the Greater Recent geological work in Colombia makes it Antillean island of Hispaniola. Presumably fairly certain that the interocean passage was cichlids in Central America have been there not across Panama but across northwestern as long and probably longer than in the Colombia. It was a wide break and obviously '''Test Indies, although this is not necessarily a thoroughly effective one insofar as the true. The Miocene fossil may have repre­ northward movements of South American sented a single early overseas colonization primary freshwater fishes is concerned. Ob· from South America. However, if it repre­ viously, none got into Panama until the sents a form derived from Central America, break was closed. Cichlas01na probably entered Central Amer­ The dating of the final closing of the ica as long ago as the Early Miocene (or Panamanian-Colombian gap has been the before) thus pushing the beginnings of result of recent work by mammalian paleon­ poeciliid evolution in Central America prob­ tologists. Patterson and Pascual (1953: 146) ably into the Oligocene. However, such rea­ said: "The long isolation of South America soning on the basis of a single extralimital ended in the late Pliocene (perhaps earliest fossil is highly dangerous. Pleistocene) when the last great episode of Andine uplift began. The Americas were GEOLOGICAL CORRELATIONS united at Panama by a continuous if narrow It now remains to be seen how the known bridge and a great exchange of mammals geological facts fit into the picture as painted got under way." The importance of this from the fish evidence. I shall not go deeply evidence is great because, of all terrestrial into the geology, for I feel that the time is animals, the paleontological history of the not ripe for such correlation, and it should mammals has been the most intensely and be made by geologists or paleontologists. broadly studied. No fossil evidence derived However, it can be said that the geological from other groups of continental organisms is evidence, and especially recent paleontolog­ presently nearly as well documented as that ical evidence derived from mammals, fits in from mammals. That there was earlier over­ with the fish evidence very well (see especially water exchange of mammals between North

122 772 COPEIA, 1966, NO.4 and South America is obvious, but the sea­ Darlington's scheme of primary freshwater barrier appears to have persisted from at fish dispersal inevitably affects his entire least as early as the Jurassic up to the very world scheme, which presupposes continen­ end of the Tertiary, and may never have tal or, rather, ocean basin stability. This been bridged until the Pliocene. is not the time or place to enter into these Primary freshwater fishes, as I have often larger questions, which I am considering else­ pointed out (Myers, 1938, 1949) cross sea­ where. However, this leaves the South Amer­ barriers with much greater difficulty than ican primary fishes without the possibility mammals and amphibians. There is there­ of northern derivation during the enormous fore good reason to believe that the invasion time period from the earlier Mesozoic to the of Central America by primary freshwater Pleistocene. I cannot believe that their an­ ostariophysans from South America is quite cestors came from any northern continent. as young as the character and ecology of the Inevitably this brings us to explanations of middle Central American fish fauna leads us marine derivation during the Cretaceous, to believe. The secondary cichlids were prob­ which there is growing reason to reject, or ably able to cross the narrowing sea-barrier to Mesozoic union of South America and before the primary ostariophysans got their Africa, which there is growing reason to necessary land bridge. And the poeciliids, accept.2 I believe continental drift to be the if they came from South America, or if they ultimate answer, and even Darlington (1964) migrated south into South America, were has very recently cautiously come out in quite as able sea navigators as the cichlids. favor of drift. I am taking up the problem of drift in relation to fish distribution else­ BROADER IMPLICATIOI\S where. I see no escape from the conclusion that Central America possessed no obligatory LITERATURE CITED freshwater ostariophysans until the Pliocene DARLINGTON, P. J., JR. 1957. Zoogeography: the or even the Pleistocene, since which time geographical distribution of animals. John the most aggressive and ubiquitous of all Wiley and Sons, New York, N. Y. 1964. Drifting continents and Late characoid genera (Astyanax) has, in a geolog­ Paleozoic geography. Proc. Nat. Acad. Sci. ical sense, raced northward to the Rio Grande, 52: 1084-1091. trailed a little more slowly by Hyphessobrycon, GREENWOOD, P. H., D. E. ROSEN, S. H. 'VEITZ;\L\N, Brycon, Roeboides, Gymnotus, and a few AND G. S. MYERS. 1966. Phyletic studies of teleostean fishes, with a provisional classifi­ others. A cichlid also has reached the Rio cation of recent forms. Bull. Am. Mus. Nat. Grande, but almost certainly its immediate Hist. 131(4):339-456. ancestors had a somewhat longer period in KOSSWIG, C. 1944. Kontinentalverschiebungs- theorie und Fischverbreitung. C. R. Ann. which to get there than the characids had. Arch., Soc. Turque Sci. Phys. Nat. Istanbul 11: The three North American primary fishes 1-28. in Guatemala cannot have been there long. ~fILLER, R. R. 1966. Geographical distribution These conclusions being accepted, it fol­ of Central American freshwater fishes. Copeia lows that the derivation of the excessively 1966(4):773-802. MYERS, G. S. 1938. Fresh-water fishes and West rich South American freshwater fish fauna, Indian zoogeography. Ann. Rep. Smith. Inst. especially the cypriniform characoids, from for 1937, Wash., D. C. Pp. 339-364. Asian immigrants which filtered through the 1949. Salt-tolerance of fresh-water fish North and Central American faunas without groups in relation to zoogeographical prob­ leaving a trace (Darlington, 1957), cannot lems. Bijdr. Dierk. 28:315-322. ---. 1963. The fresh-water fish fauna of be seriously entertained. Cypriniform fishes North America. Proc. XVI Internal. Congr. do not filter through a fauna without leaving Zool. 4:15-20. traces, as Darlington presumed. They take PATTERSON, B. Al\'D R. PASePAL. 1963. The ex­ over continental faunas and tend to "swamp tinct land mammals of South America. Pro- out" other groups, becoming the dominant element of the fauna. And what fossil evi­ 2 I know of only one attempt by an ichthyologist to explain freshwater fish dispersal by means of conti­ dence we have about them indicates that, nental drift (Kosswig, 1944). Unfortunately, Kosswig morphologically and presumably ecologically, was unfamiliar with such important publications bearing on drift as those of du Toit, and he was obviously un­ they have changed but little since the earli­ acquainted with much of the extensive mammalian and est Cenozoic. other tetrapod evidence. In the face of that evidence, Kosswig's geological timing is so inacceptable that grave This negation of one of the main points of doubt is cast upon all features of his ingenious scheme.

123 MYERS-CENTRAL AMERICAN FISH FAUNA 773

gram, XVI Internat. Congr. Zool. Pp. 138- Antillean-Caribbean region. John Wiley and 148. Sons. New York, N. Y. ROSEN, D. E. AND R. M. BAILEY. 1963. The WEYL, R. 1961. Die Geologie Mittelamerikas. poeciliid fishes (Cyprinodontifonnes), their Beitr. region. GeoI. Erde. Bd. 1, 266 pp. structure, zoogeography, and systematics. Bull. Am. Mus. Nat. Hist. 126(1):1-176. DIVISION OF SYSTEMATIC BIOLOGY, STANFORD SCHUCHERT, C. 1935. Historical geology of the UNIVERSIlY, STANFORD, CALIFORNIA 94305.

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