A Zoogeographic Study and the Taxonomy of the Xenodontine Colubrid Snakes by Janann Jenner A dissertation in the Department of Biology submitted to the Faculty of the Graduate School of Arts and Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy at New York University. May, 1981 Approved Herndon G. Dowling Professor Department of Biology Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright (c) 1981, Janann Jenner - ii - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS The author gives special thanks to: - Dr. Herndon G. Dowling, sponsor and teacher. His generosity, thoughtfulness, and patient support during the preparation of this thesis has created a debt that can never be adequately repaid. - John Fuchs and Itschak Gilboa, City University Computer Center, who designed the computer software necessary to produce the computer maps. - George Foley, Dr. Charles W. Myers, and Margaret Shaw, Department of Herpetology, American Museum of Natural History, who allowed the use of the herpe- tological literature citation cross-index. - Frances Irish, Dr. Roy McDiarmid, and Dr. George Zug, Department of Herpetology, United States National Museum, who allowed the use of specimens and library. - The Department of Biology of New York University for financial support. - The New York University Computer Center for fin­ ancial support. - Herpetological Information Search Systems (HISS) for use of hemipenis drawings. - Dr. Irving Brick, Dr. Calvin Heusser, Dr. Joseph LoBue, Dr. Janis Roze, Dr. Fleur Strand, members of my doctoral committee, for their helpful criticisms. - iii - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. - Karen Anderson, Barbara Pytel, Lisa Levinson, and Esther Indelman, herpetology graduate students, who made suggestions during the final preparation of this thesis. - Dr. Barbara Brummer and Tom Brummer who encouraged me that someday this thesis would be finished and pulled me back from the window ledge many times. - Richard Carter, William Elek, Miesje Jolley, Allerton Kilbome, Verna Koons, Lanette McAndrews, James McAndrews, Melanie Perish, Bernie Weinstein, and Dr. Lou Wise who were never too busy to listen to my woes and offer encouragement. - iv - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Author: Janann Jenner Title: A Zoogeographic Study and the Taxonomy of the Xenodontine Colubrid Snakes Research Advisor: Herndon G. Dowling, Professor of Biology, New York University. Morphological and geographic analysis of the xeno­ dontine colubrid snakes demonstrated that previous tribal criteria as well as tribal allocations were erroneous. Two previous tribes are not accepted. Four new tribes are des­ cribed. Four genera (Scolecophis, Simophis, Tantilla, and Tri- morphodon) were transferred to the Subfamily Colubrinae. Genera with flounced hemipenes (Conophis, Ialtris, Pseudo- eryx and some species of Atractus and of Coniophanes) as well as those genera with inadequate hemipenial descrip­ tions (Ditaxodon, Elapomojus, Hydromorphus, Lioheterophis, Parapostolepis, Paraptychophis, Platynion, and Tantillita) cannot be properly assigned to xenodontine tribes. The remaining xenodontine genera are allocated to seven tribes. Each tribe has a distinctive hemipenial con­ figuration and a cohesive geographic range. Tribal criteria and allocations are as follows: Tribe Alsophiini is defined by possession of a bilobed, - v - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. semicapitate hemipenis with proximal spines, distal caly­ ces, and forked sulcus. Its geographic distribution is centered in Hispaniola. Alsophis, Antillophis, Arrhyton, Farancia, Helicops, Heterodon, Hydrodynastes, Hypsirhynchus, Uromacer, and Uromacerina are allocated to Tribe Alsophiini. Tribe Diaphorolepini is defined by possession of an entirely spinose, noncapitate hemipenis with a forked sul­ cus. Its geographic distribution is centered in southern South America. Atractus, Chersodromus, Crisantophis, Dia- phorolepis, Elapomorphus, Enulius, Gomesophis, Pseudotom- odon. Ptvchophis. and Sordellina are allocated to Tribe Diaphorolepini. Tribe Dipsadini is defined by possession of a fully capitate hemipenis wit; proximal spines and a forked sul­ cus. Its geographic distribution is centered in Central America. Adelphicos, Coniophanes, Cryophis , Dipsas, Geo- phis , Ninia, Pliocercus, Rhadinaea, Sibon, Sibynomorphus, Tretanorhinus, Trimetopon, and Tropidodipsas are allocated to Tribe Dipsadini. Tribe Leptodeirini is defined by possession of a fully capitate, single or bilobed hemipenis with a simple sul­ cus. Its geographic distribution is centered on the north­ ern Pacific coast of Mexico. Eridiphas, Hypsiglena, Iman- todes, and Leptodeira are allocated to Tribe Leptodeirini. Tribe Philodryini is defined by possession of a - vi - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bilobed or single, noncapitate hemipenis with a forked sulcus, proximal spines, and distal calyces. Its geo­ graphic distribution is centered in southern South Amer­ ica. Amastridium, Apostolepis, Calamodontophis, Carphophis Contia, Diadophis, Hydrops, Manolepis, Nothopsis, Philo- dryas, Pseudablabes, Synophis, Tachymenis, Thamnodynastes, Tomodon, and Xenopholis are allocated to Tribe Philodryini. Tribe Pseudoboini is defined by possession of a bi­ lobed, bicapitate hemipenis with a forked sulcus. Its dis­ tribution is centered in Matto Grosso, Brazil,and adjacent Bolivia. Clelia, Drepanoides, Oxyrhopus, Phimophis, Pse­ udoboa, Rhachidelus, Saphenophis, Siphlophis, Tripanurgos. and Tropidodryas are allocated to Tribe Pseudoboini. Subfamily Xenodontinae is partitioned into northern and southern units. Alsophiini, Dipsadini, and Leptodeir­ ini are northern tribes, while Diaphorolepini, Philodry­ ini, Pseudoboini, and Xenodontini are southern tribes. Geo­ graphic patterns, latitudinal distributions, maxillary den­ tition, length of maxilla, and mode of scale row reduc­ tion support the existence of northern and southern xenodon tines. It is hypothesized that Subfamily Xenodontinae orig­ inated from a lycodontine ancestor which had an entirely spinose hemipenis with a forked sulcus. Tribe Diaphorolep­ ini retains this ancestral hemipenial configuration. The ancestors of Tribe Philodryini developed calyces on other- - vii - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. wise spinose hemipenes. Calyces were restricted to the apices of the lobes of the hemipenes of Tribe Pseudoboini. Disked hemipenes developed in the Xenodontini. The north­ ern tribes originated from a philodryine ancestor and spread from northern South America to the Lesser and Greater Ant­ illes and northward into North America. Alsophines iso­ lated in Middle America developed the capitate hemipenis and became dipsadines. Dipsadines which lost one fork of the sulcus became the leptodeirines. Dipsadines and lepto- deirines dispersed to South America after the isthmian con­ nection was established in the late Pliocene. - viii - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONTENTS Page Acknowledgements ---------------------------------------- iii Abstract ------------------------------------------------ v List of Tables ------------------------------------------ xiii List of F i g u r e s ------------------------------------------ xvi I. Background------------------------------------------- 1 A. Colubrid Snake Taxonomy ------------------------- 1 B. Historical Review -------------------------------- 2 1. Cope's Contributions ------------------------- 2 2. D u n n ------------------------------------------- 3 3. Underwood ------------------------------------- 3 4. D o w l i n g ---------------------------------------- 8 C. Subfamily Xenodontinae -------------------------- 8 D. Hemipenes ----------------------------------------- 11 E. Xenodontine Hemipenes --------------------------- 13 F. Other Xenodontine Characters -------------------- 15 G. Rationale for Present W o r k ---------------------- 17 H. Importance of Zoogeography to Systematics------- 18 I. Zoogeography of Xenodontine Tribes ------------- 19 1. Factors Influencing Xenodontine Distributions --------------------------------- 19 2. Physiography of Mexico and Central America -- 20 3. Physiography of South America ---------------- 22 4. Plate Tectonics ------------------------------- 25 - ix - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5. Continental Drift: The Global History -- 27 6. Tectonics and Drift in the Western Hemisphere -------------------------------- 29 7. Conclusions from Paleogeography-------- 33 8. Effects of Continental Drift ------------ 34 9. Temperature and Precipitation----------- 35 10. Climate ----------------------------------- 36 11. Climatic Regimes ------------------------- 38 12. History of Climatic Change -------------- 43 13. Vegetation ------------------------------- 44 14. Biotic Provinces ------------------------- 53 15. Importance of the Genus to Zoogeographic Analysis ------------------- 57 II. Materials and Methods ------------------- 59 A. Map Construction-------------------------------