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The Turtles of Mexico
Land and Freshwater Forms
By John M. Legler, Richard C. Vogt UNIVERSITY OF CALIFORNIA PRESS
Copyright © 2013 The Regents of the University of California
All rights reserved.
ISBN: 978-0-520-95689-6
CHAPTER 1
TURTLES
A PARADIGM OF VARIABILITY, VENERABILITY, AND VULNERABILITY
Introduction
Objectives
This book concerns the diverse chelonian fauna of Mexico: 15 families, 14 genera, 38 species, and 66 terminal taxa of freshwater and terrestrial chelonians occurring within the political boundaries of Mexico (Los Estados Unidos de Mexico). These represent all of the families of nonmarine cryptodires that occur in the Western Hemisphere.
The authors of this book (hereinafter JML and RCV) have a cumulative experience of nearly a century with chelonian studies in general and with Mexican turtles in particular.
Smith and Smith (1979) gave complete and accurate synonymies for all Mexican testudinates and we make no attempt to do so. The current book makes no significant taxonomic decisions; it attempts to present an account of the species occurring in Mexico with easily used keys and distribution maps, and to cover what is known of their natural history.
Our use of recent nomenclature at the genus and species level, where there is a choice, is conservative. We have tried to separate the identification of specimens from the diagnosis of taxa. Keys are based chiefly on external characters and are made to be used with whole specimens. They do not, as Ernest Williams once put it, require "X-ray vision." Diagnoses may, however, rely heavily on morphological states, often osteology, that cannot easily be perceived outside of a good museum or without dissection.
We hope this book will serve as a one-stop guide, a vade mecum, for those who will study and learn new things about Mexican turtles and turtles in general. We hope the book will also foster communication among persons who study turtles as a hobby and those who consider it a profession.
Most of the available information on Mexican turtles concerns taxonomy and geographic distribution, and it is at this point that most of the knowledge of Mexican chelonians rests. We seek to remedy this situation by organizing what is known about their natural histories and augmenting this information with inferences drawn from the same species or closely related species in countries other than Mexico (usually the United States).
We seek particularly to stimulate studies of turtles in Mexico by Mexican students of cheloniology. Our hope is that this book will encourage many substantial studies of natural history such as the few that have been done at this point (Terrapene coahuila by Brown, 1974; Gopherus flavomarginatus by Morafka and colleagues, 1980–1997; and studies of various neotropical species by Vogt and students, 1980–2011 and several unpublished theses in English and Spanish such as Dean [1980, on Staurotypus salvini] and Zenteno-Ruiz 1993 and 1999). Above all, we wish to chronicle what is currently known about Mexican turtles before their extinction, a possibility that is being hastened by human works.
Although we have consulted and cited an extensive body of literature, much of our information is gleaned from our own, previously unpublished sources—personal observations, field notes, and databases.
The History of Turtle Biology in Mexico
The progression of knowledge of the turtle fauna of Mexico has followed a familiar path, beginning with basic exploration during which a few taxa were named from an occasional specimen reaching one of the large overseas museums. The type specimens of Dermatemys mawi and Trachemys scripta ornata were obtained by British naval officers. Descriptions were made by scientists who knew little about the country of origin. Eventually, there were zoological explorations and floral and faunal surveys with paid collectors who sent their material to overseas institutions. Even then the collector or purveyor and the describing scientist were never the same. Localities often were vague, and natural history information was nonexistent or ignored in taxonomic descriptions, a circumstance that persisted into the early 1950s.
Turtles were typically no more than addenda to larger general collections, probably because they were difficult to obtain, bulky, and difficult to preserve. Special techniques for their study, capture, and preservation had not been developed. New taxa were commonly described from one or two specimens, the provenance of which was unknown or based on dubious information. Series of specimens were almost never available, sought, or valued, and information from dissections and viscera was not routinely harvested. More than half of the Mexican turtles described from 1827 to 1985 were from type localities outside Mexico and were subsequently shown to occur in Mexico.
From 1758 to 1895, European workers described 20 of the 31 new chelonian taxa and workers in the United States described 11. There was a hiatus in activity from 1895 to 1922 when no new taxa were described, including during World War I. From 1922 to 1997, 29 new taxa were described, all by workers in the United States. This change reflected the ascendancy of science in the New World, which, in turn, was correlated with discovery, colonization, and the establishment of academic institutions—the coming of age of North American science following a period of European hegemony.
Hobart M. Smith (HMS), Rosella B. Smith (RBS), and E. H. Taylor and associates ushered Mexican herpetology into the 20th century by making, studying, and reporting on huge general herpetological collections (somewhere in excess of 30,000 specimens gathered in Mexico from 1932 to 1941, with HMS and RBS concentrating the work from 1938 to 1941). This firmly established the course of Mexican herpetology but not the study of Mexican turtles. There were fewer than 100 turtles in the collection (pers. comm., H. M. Smith). An impressive total of 752 scientific papers resulted from these collections but included no substantive papers on turtles. Knowledge of Mexican turtles achieved a logical plateau in the annotated checklist of Smith and Taylor (1950). Virtually no information was available on natural history at the time.
In retrospect, the foregoing statistics clearly signaled that "general" herpetological collecting in Mexico (or anywhere) would not produce the wherewithal for erudite studies of a chelonian fauna. At the middle of the 20th century, all biological knowledge of chelonians lagged at least 50 years behind that for other groups of vertebrates. This lag was directly correlated with the lack of adequate collections and special techniques for study.
A significant change was affected in the last 40 years of the 20th century. Turtle specialists (mostly young, all zealous) at U.S. universities made expeditions specifically to study and collect turtles, developed their own techniques, and published their own accounts of the results. Among these were James F. Berry, John Iverson, John M. Legler, and Robert G. Webb, whose names were included in the authorship of 14 of the 16 new taxa of Mexican turtles in the years 1959 to 1997 (see Literature Cited). In this same period, Brown (1974) conducted a detailed autecological study of Terrapene coahuila, Morafka and McCoy (1988) spearheaded natural history and conservation studies of Gopherus flavomarginatus in the Bolsón de Mapimí, and Vogt and his students (e.g., Vogt and Flores-Villela, 1992a,b; and Vogt, 1990) began long-term studies of aquatic turtle populations in neotropical Mexico. This surge of interest and activity in a formerly moribund field has persisted to the present time.
Chelonian Studies by Mexican Biologists
Although Mexican biologists have not described new taxa of turtles, they have contributed significantly to the literature on Mexican chelonians.
Professor Eduardo Caballero y Caballero (Universidad Nacional Autónoma de México, or UN AM) published numerous papers on the intestinal parasites of freshwater turtles from various parts of Mexico over a period of about 30 years, one of the earliest (Caballero y Caballero and Sokoloff, 1935) being on Dermatemys mawi.
Don Miguel Álvarez del Toro (1917–1996) originally from Colima, studied the natural history of Chiapas beginning in 1942. Although he had no formal education, he was an outstanding naturalist with a predilection for freshwater turtles and held honorary doctorates from the Universities of Chiapas and Chapingo. He developed a modern zoo in Tuxtla Gutiérrez that includes his name (ZOO MAT). His notable contributions were his early observations of Dermatemys in the Rio Lacantún (Álvarez del Toro, 1960) and comments on economic use of turtles in Chiapas (Álvarez del Toro, et al., 1979). He published three editions of a book, Los Reptiles de Chiapas (1960, 1973, and 1982) that included natural history data on turtles. A fourth greatly expanded edition was prepared (edited by RC V) but never published. The zoo in Tuxtla Gutiérrez (ZOO MAT) maintains breeding populations of native Chiapan turtles, and the keepers there continue to record observations. Don Miguel was also well known for his studies of arachnids, birds, and mammals.
Studies of Mexican freshwater turtles by Gustavo Casas-Andreu (Instituto de Biología, UN AM) culminated in the publication (1967) of a useful work that included illustrations (19 plates), keys, descriptions, geographic distributions with maps, and notes on natural history. Subsequently, his students have undertaken various projects on Mexican turtles. One of his prominent students, Oscar Flores-Villela, wrote an undergraduate thesis that included Mexican freshwater turtles (Flores-Villela, 1980) and then began studies of the ecology of Claudius angustatus, under the supervision of RC V, which was extended and completed as a master's thesis by Veronica Gonzáles Espejel (2004) (Instituto de Ecología, Jalapa). Oscar Flores-Villela wrote a doctoral thesis on biogeography of a regional Mexican herpetofauna and was an author on several publications concerning turtles in southern Mexico based on data collected from 1980 to 1988 (Flores-Villela and Vogt, 1984, 1992a; Vogt and Flores-Villela, 1992b). Flores is currently coordinating an atlas of the herpetofauna of Mexico and is professor and curator of the chief herpetological collection at UNAM—Muséo de Zoologia, Facultad de Ciencias.
A work on the herpetofauna of coastal Jalisco by Garcia Aguayo and Ceballos (1994) contained observations on freshwater turtles.
Dr. Gustavo Aguirre-León and associates (Instituto de Ecología A. C., Jalapa, Veracruz) have continued and extended the studies of Gopherus flavomarginatus in the Bolsón de Mapimí (see citations in account of Gopherus flavomarginatus). He and his students have also continued the long-term studies of several aquatic turtles that were begun by Vogt and students in 1980. Others continuing these projects are Claudia Zenteno and students (Universidad Juárez Autonoma de Tabasco) and Carlos Guichard (ZOO MAT, Tuxtla Gutiérrez, Chiapas).
According to Flores-Villela, Smith, and Chiszar (2004), a total of about 70,000 specimens of reptiles and amphibians exists in 20 Mexican collections. Only a few of these are turtles. The largest collection of turtles in Mexico, some 1200 specimens, was made and curated by Vogt during his tenure (1980–2000) at the Estación de Biología Tropical Los Tuxtlas, San Andres Tuxtla, Veracruz. After his departure for Brazil, there was little interest in the collection, and it was given to a private foundation in the United States.
Other Books on Turtles
Turtles form a small, unique group and have been a favorite subject for scientists and popular writers. The works of Walbaum (1782) and Schoepff (1792–1801) on turtles constitute the earliest monographs on any group of reptiles. The 19th century brought forth works such as those by Bell (1831) and Sowerby and Lear (1872) in which artfully crafted plates, often hand colored, were self-standing but text, if any, was simply an addendum. Most works on turtles of this period were attempts to survey the turtles of the world and were based on museum collections.
In an intermediate category was Louis Agassiz's classic Contribution to the Natural History of the United States of America. First Monograph, which comprised three parts bound in two volumes (1857a and 1857b). Parts II and III were on turtles and consisted of extensive text containing accounts of what was then known of form, function, growth, sexual dimorphism, fossils, and some life history, followed by the most complete account of chelonian embryology and organogenesis of the time. These parts of the book were only slightly clouded by part one in which his creationist views (following his mentor, G. Cuvier) were espoused. Parts II and III are best known for their 34 exquisite supporting plates (by artists A. Sonrel and H. J. Clark), seven of life-sized neonates and eggs, 18 on developmental stages, and two in color of Trachemys and Pseudemys. The accounts and illustrations included at least nine taxa that were later shown to occur in Mexico. The book is a compendium that stands as a landmark of utility and excellence for 19th-century cheloniology.
Books exclusively devoted to turtles and relying mostly on what appeared in the text were characteristic of the 19th century. In the years before the current work, books devoted to turtles have consisted chiefly of textual information and were illustrated by photographs and line drawings. These works initiated an era characterized by far less elegance of illustration but far more information in the text. Three of these (Pritchard 1967, 1979; Ernst and Barbour, 1989) were on turtles of the world, and four were on turtles of the United States and Canada (Pope, 1939; Carr, 1952; Ernst and Barbour, 1972; Ernst et al., 1994). Four annotated checklists of great utility have appeared: Iverson (1992a) contains maps and cladograms but no drawings; Wermuth and Mertens (1961) lacks maps but has useful line drawings of most taxa; Smith and Taylor (1950) presented keys, brief synonymies, and geographic distributions for the turtles of Mexico; Bickham et al. (2007) produced a summary of taxonomy and nomenclature that we have usually followed in this book.
It was Carr (1952) who set a modern trend in writing both knowledgeably and delightfully about turtles. His book has been an inspiration for the current book. The only prior work devoted solely to the turtles of Mexico (Smith and Smith, 1979) also stands as the most thorough account ever prepared on the literature, taxonomy, and geographic distribution of turtles in a major region of the world.
The Definition of a Turtle
Turtles are members of the Order Chelonia (also termed Testudines or Testudinata). The distinction of turtles as a unique group of the Class Reptilia and the monophyly of the group has never seriously been questioned. The geographic distributions of humans and turtles overlap broadly, and turtles are familiar to humans. There is a word for "turtle" in most languages, and many children can draw a crude (but diagnostic) picture of a turtle before they can spell the word. If turtles were known only from fossils, they would be regarded with substantially more awe than they are as familiar animals.
The most common English names for members of the order are turtle, tortoise, and terrapin. Each name may have a special significance in local areas, but all are vernacular. The terms turtle, testudinate, and chelonian are commonly used in reference to all members of the order. The word tortoise is used by most turtle biologists in reference to the completely terrestrial testudinids—but in Australia for any member of the Family Chelidae.
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Excerpted from The Turtles of Mexico by John M. Legler, Richard C. Vogt. Copyright © 2013 The Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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