Glyptodonts of North America

FRONTISPIECE.—-Reconstruction of Glyptolherium anzonae. SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY • NUMBER 40 Glyptodonts of North America David D. Gillette and Clayton E. Ray ISSUED DEC 211981 SMITHSONIAN PUBLICATIONS SMITHSONIAN INSTITUTION PRESS City of Washington 1981 ABSTRACT Gillette, David D., and Clayton E. Ray. Glyptodonts of North America. Smithsonian Contributions to Paleobiology, number 40, 255 pages, 97 figures, 70 tables, 1981.—All known North American glyptodonts belong in the genus Glyptothenum Osborn, 1903 (Family Glyptodontidae, Subfamily Glyptodon- tinae). Junior synonyms are Brachyostracon Brown, 1912; Boreostracon Simpson, 1929; Xenoglyptodon Meade, 1953; and all assignments of North American specimens to Glyptodon Owen, 1838. The ancestral species is Glyptothenum texanum from the Early Pleistocene Tusker (Arizona) and Blanco (Texas) local faunas of the Blancan Land Mammal Age; G texanum is smaller and lacks many of the exaggerated features of the descendant species. The descendant species are G. anzonae (Blancan? and Irvingtonian); G. floridanum (Ranchola- brean); and two species known from isolated localities in Mexico, G. cyltndricum and G. mexicanum. The taxonomic validity of G. mexicanum is questionable. The geographic distribution and faunal associations of Glyptothenum clearly indicate tropical or subtropical habitats. North American glyptodonts exhibit extreme tendencies toward hypsodonty and homodonty in the dentition, and they lack both incisiform and caniniform teeth. They probably fed on soft vegetation near permanent bodies of water. Graviportal limb proportions and details of the gross osteology suggest slow and cumbersome locomotion, which probably precluded occupation of upland habitats. A substantial expansion in the number of specimens available for study has extensively improved our knowledge of the gross osteology of Glyptothenum. especially for G. texanum and G. anzonae. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The trilobite Phacops rana Green. Library of Congress Cataloging in Publication Data Gillette, David D. Glyptodonts of North America. (Smithsonian contributions to paleobiology ; no. 40) Bibliography: p. Supt. of Docs, no.: SI 1.30:40 1. Glyptodontidae. 2. Paleontology—North America. I. Ray, Clayton Edward, joint au thor. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to paleo biology; no. 40. QE701.S56 no. 40 IQE882.E2] 560s [569'.31) 80-607040 Contents Page Preface v Introduction 1 Previous Work 3 Systematics 5 Subfamily GLYPTODONTINAE 10 Genus Glyptothenum Osborn . 10 Glyptothenum texanum Osborn . 11 Glyptothenum anzonae Gidley 12 Glyptothenum flondanum (Simpson), new combination 14 Glyptothenum cylindncum (Brown), new combination 15 Glyptothenum mexicanum (Cuataparo and Ramirez), new combination 16 Distribution 18 Osteology 27 Skull 27 Presacral Axial Skeleton 68 Front Limb 81 Pelvis 112 Hind Limb 124 Caudal Vertebrae 162 Carapace 168 Caudal Armor 194 Selected Aspects of Glyptodont Paleobiology 199 Functional Morphology 200 Habitat 207 Evolutionary History of Glyptothenum 208 Conclusions 209 Appendix: Tables of Measurements 212 Literature Cited 252 m We respectfully dedicate the present monograph to the late Ted Galusha, whose expert field work made this revision possible. Preface "Mother," he said, "there are two new animals in the woods today, and the one that you said couldn't swim, swims, and the one that you said couldn't curl up, curls; and they've gone shares in their prickles, I think, because both of them are scaly all over, instead of one being smooth and the other very prickly; and besides that, they are rolling round and round in circles, and I don't feel comfy." "Son, son," said Mother Jaguar ever so many times, graciously waving her tail, "a Hedgehog is a Hedgehog, and can't be anything but a Hedgehog; and a Tortoise is a Tortoise, and can never be anything else." "But it isn't a Hedgehog, and it isn't a Tortoise. It's a little bit of both, and I don't know its proper name." "Nonsense!" said Mother Jaguar. "Everything has its proper name. I should call it 'Arma dillo' till I found out the real one. And I should leave it alone."—Rudyard Kipling, "The Beginning of the Armadillos" Had Kipling chronicled the Pleistocene instead of modern times, he no doubt would have passed over the armadillos in this parable for the even more bizarre glyptodonts. For these extinct creatures of the past outwardly resem bled modern armadillos and turtles, and ecologically perhaps represented an animal somewhere between a land tortoise and a hippopotamus. Just as armadillos today are among the strangest of mammals, the glyptodonts of the Pleistocene, representing a branch of the same order, present a perplexing combination of unlikely characters. If their fossil remains had gone undiscov ered, glyptodonts could only have been the product of a poet's imagination, for their very existence could never be predicted within the confines of modern science and logic. Their improbable existence notwithstanding, glyptodonts comprised an important southern group of characteristic North American mammals of the Pleistocene Epoch. They were large and cumbersome, dwarfing the largest of modern armadillos. In many respects their anatomy reflects extreme adaptation for massive build and heavy weight. They have no living counterparts, except within our poetic imagination. Picture, if you will, a giant tortoise as a mammal, behaving as a lowland herbivore, with kinship to armadillos and the extinct ground sloths. Such are the glyptodonts, the North American representatives of which are reviewed here. FICURE 1.—Schematic illustration of skeleton oi Glyptothenum anzonae (modified for Glyptothenum after Burmeister and Hoffstetter). Glyptodonts of North America David D. Gillette and Clayton E. Ray Introduction found in other mammalian skulls. The bones surrounding the dental battery (maxilla, pala The extinct group of edentates commonly tine) are vertically expanded to accommodate the called "glyptodonts" (Greek: "carved tooth" or peculiar dentition, while bones of the basicran- freely, "grooved tooth") has perplexed students of ium are brachycephalic. The skull roof was pro natural history since their discovery early in the tected by an articulated set of dermal bones or 19th century. These former occupants of the New "cephalic shield." We propose that there was a World tropics and subtropics combine an unlikely large fleshy snout or a proboscis similar to that array of characteristics usually considered unique found in elephants, tapirs, and pyrotheres. to other vertebrates. The predominant feature is The legs, especially the hind limb, are elephan their turtle-like shell, or carapace (Figure 1). Dif tine. Glyptodonts surpass the proboscidean pro fering from the typical armadillo armor by being portions classically illustrated as graviportal and almost entirely immobile, the glyptodont cara represent one of the "most graviportal" groups pace afforded excellent protection. Attendant ever to have lived. Their large tail probably specializations in the axial skeleton are conver functioned as a counterbalance in locomotion, as gent with chelonian anatomy: extensive fusion of an accommodation for the lack of pelvic and most of the vertebral column and fusion of the axial mobility. The caudal vertebrae of the North pelvic girdle to the carapace, rendering the pelvis American representatives were encased in com entirely immobile. plete articulating rings of bony scutes. Despite The glyptodont dentition resembles in its con some reconstructions for North American glyp struction that found in certain rodents, notably todonts showing an elaborate terminal mace, this microtines and capybaras. But glyptodont teeth construction is found only in some of their South lack enamel, as do those of other edentates, and American relatives. Instead, the tail of North glyptodonts also lack incisiform and caniniform American representatives ended in a blunt ter teeth. Glyptodont cheek teeth are the "most hyp- minal tube formed by the fusion of two or three sodont" and the "most homodont" among terres caudal rings. trial mammals. Classically included as members of the extinct The glyptodont skull has modifications not Pleistocene megafauna, glyptodonts reached David D. Gillette, Shuler Museum of Paleontology, Department of North America relatively late in the history of the Geological Sciences, Southern Methodist University, Dallas, Texas family. Already diversified and widespread in 75275. Clayton E. Ray, Department of Paleobiology, National Mu South America in the Miocene, it was at the close seum of Natural History, Smithsonian Institution, Washington, D. C. 20560. of the Pliocene Epoch or perhaps in the earliest SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Pleistocene that glyptodonts finally invaded for at least two other North American species, North America. There they experienced only and probably for two others as well. Without modest success, surviving until the Late Pleisto these specimens and the courteous assistance pro cene. The North American representatives are vided by members of the American Museum of descendants of probably a single invasion of their Natural History, in particular that of Mr. Galu South American relatives into Central America. sha, this study could never have been initiated, Subsequent evolution from this early Pleistocene

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