Genera and Subgenera of Chipmunks

Part 1

Produced by Chris Curnow, Joseph Cooper, Anne Storer and the Online Distributed Proofreading Team at http://www.pgdp.net

Genera and Subgenera of Chipmunks BY JOHN A. WHITE

University of Kansas Publications Museum of Natural History

Volume 5, No. 32, pp. 543-561, 12 figures in text

December 1, 1953

University of Kansas LAWRENCE 1953

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, and Robert W. Wilson

Volume 5, No. 32, pp. 543-561, 12 figures in text

December 1, 1953

UNIVERSITY OF KANSAS Lawrence, Kansas

PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1953

Genera and Subgenera of Chipmunks By JOHN A. WHITE

CONTENTS

PAGE Introduction 546 Historical 546 Methods, Materials, and Acknowledgments 547 Evaluation of Characters 548 Characters in which the Subgenera Eutamias and Neotamias Agree, but Differ from the Genus Tamias 548 Structure of the Malleus 548 Structure of the Baculum 549 Structure of the Hyoid Apparatus 552 Presence or Absence of P3 553 Length of Tail in Relation to Total Length 553 Color Pattern 554 Characters in which the Subgenus Eutamias and the Genus Tamias Agree, but Differ from the Subgenus Neotamias 554 Shape of the Infraorbital Foramen 554 Width of the Postorbital Process at Base 554 Position of the Supraorbital Notch 554 Degree of Convergence of the Upper Tooth-rows 554 Degree of Constriction of the Interorbital Region 555 Shape of the Pinna 555 Structural Features that are too Weakly Expressed to be of Taxonomic Use 555 Discussion 555 Genera and Subgenera 557 Genus Eutamias Trouessart 557 Subgenus Eutamias Trouessart 558 Subgenus Neotamias Howell 558 Genus Tamias Illiger 559 Discussion 559 Conclusions 560 Literature Cited 561

ILLUSTRATIONS

Figs. 1-3. Dorsomedial Views of Malleus 549 Figs. 4-10. Lateral Views of Baculum 551 Figs. 11-12. Ventral Views of Hyoid Apparatus 552

INTRODUCTION

The supraspecific categories of the chipmunks, as in most other groups of squirrels, have been a source of controversy for many years. Before presenting new evidence and a review of older evidence bearing on the problem, it seems desirable to review briefly in chronological order, the taxonomic history of the genera and subgenera of the chipmunks.

HISTORICAL

Linnaeus (1758:64) described the eastern North American chipmunks under the name Sciurus striatus and based his description on that of Catesby (1743:75). The Asiatic chipmunk was first described, under the name Sciurus sibiricus, by Laxmann (1769:69). Schreber (1785, 4:790) separated the Asiatic and North American chipmunks into the Asiatic and American varieties. Gmelin (1788:50) followed Schreber and, employing trinomials, used the names Sciurus striatus asiaticus and S. s. americanus. Illiger (1811:83) proposed Tamias as the generic name of the chipmunk of eastern North America. Say (1823:45) described Sciurus quadrivittatus, the first species of chipmunk known from western North America.

Trouessart (1880:86-87) proposed Eutamias as the subgeneric name to include the western North American and Asiatic chipmunks.

Merriam (1897:189-190) raised Eutamias to full generic rank. In so doing he neither listed nor described any characters but wrote that "it will be observed that the name Eutamias, proposed by Trouessart in 1880 as a subgenus of Tamias is here adopted as a full genus. This is because of the conviction that the superficial resemblance between the two groups is accidental parallelism, in no way indicative of affinity. In fact the two groups, if my notion of their relationship is correct, had different ancestors, Tamias being an offshoot of the ground-squirrels of the subgenus Ictidomys of Allen, and Eutamias of the subgenus Ammospermophilus, Merriam."

Howell (1929:23) proposed Neotamias as the subgeneric name for the chipmunks of western North America, of the genus Eutamias.

Ellerman (1940, 1:426) gave Eutamias and Neotamias equal subgeneric rank with Tamias under the genus Tamias; on pages 427-428 he quoted Merriam, as I have done above, and later, after quoting the key to the genera and subgenera of chipmunks of Howell (1929:11), Ellerman wrote (op. cit.: 428-429), "This key convinces me that all these forms must be referred to one genus only. The characters given to separate 'Eutamias' from Tamias are based only on the absence or presence of the functionless premolar, and on the colour pattern. If colour pattern is to be used as a generic character, it seems Citellus suslicus will require a new name when compared with C. citellus, etc." And again, "The Asiatic chipmunk is intermediate between typical Tamias and the small American forms in many characters." To substantiate this, Ellerman (loc. cit.) quotes Howell (loc. cit.), in comparing the subgenera Eutamias and Neotamias, as follows: "'the ears [of subgenus Eutamias] are broad, rounded, of medium height, much as in Tamias; postorbital broad at base, tapering to a point, much as in Tamias; interorbital constriction slight, as in Tamias; upper molariform tooth rows slightly convergent posteriorly, as in Tamias.'" Ellerman (loc. cit.) again quotes Howell (loc. cit.), "'Eutamias of Asia resembles Tamias of North America and differs from American Eutamias in a number of characters, notably the shape of the anteorbital foramen, the postorbital process, the breadth of the interorbital region, the development of the lambdoidal crest, and the shape of the external ears. On the other hand, American Eutamias agrees with the Asiatic members of the genus in the shape of the rostrum, the well-defined striations of the upper incisors, the presence of the extra peg-like premolar, and in the pattern of the dorsal stripes.'"

Bryant (1945:372) wrote, "I am convinced that Ellerman's interpretation of the relationships of the chipmunks is correct." After commenting that the presence or absence of P3, "is of significance only in distinguishing between species of squirrels," Bryant adds that "The other differences between the eastern and the western chipmunks do not appear to be of sufficient phylogenetic importance to warrant the retention of the two groups as genera."

METHODS, MATERIALS, AND ACKNOWLEDGMENTS

Characters previously mentioned in the literature as having taxonomic worth for supraspecific categories of chipmunks were checked by me on specimens old enough to have worn permanent premolars. Some structural features not previously used were found to have taxonomic significance. The baculum in each of the supraspecific categories of sciurids of North America was examined; the bacula were processed by the method described by White (1951:125) to obviate "variation" caused by shriveling of the smaller bacula or breaking of the more delicate parts of the larger bacula. Mallei and hyoid bones of the genera and subgenera of the chipmunks were mostly studied in the dry state. Part of the hyoid musculature in these same groups of chipmunks was dissected.

Part 2

In all, I studied more than 1,000 skulls and skins of the subgenus Neotamias, approximately 50 skulls and skins of Tamias striatus, and 15 skulls and skins of the subgenus Eutamias (Eutamias sibiricus asiaticus from Manchuria). Numerous other specimens were examined but not in such detail.

I am grateful to Professor E. Raymond Hall for guidance in the study. For encouragement and advice I am grateful also to Doctors Robert W. Wilson, Cecil G. Lalicker, Edwin C. Galbreath, Keith R. Kelson, E. Lendell Cockrum, Olin L. Webb, and others at the Museum of Natural History, and in the Department of Zoology of the University of Kansas. My wife, Alice M. White, made the drawings and helped me in many other ways. For lending specimens I thank Dr. David H. Johnson of the United States National Museum, and Dr. George C. Rinker of the Department of Anatomy, University of Michigan.

Assistance with field work is acknowledged from the Kansas University Endowment Association, the National Science Foundation, and the United States Navy, Office of Naval Research, through contract No. NR161 791.

EVALUATION OF CHARACTERS

The following paragraphs treat the characters listed by Howell, Ellerman, and Bryant, and such additional characters as I have found useful in characterizing the genera and subgenera of chipmunks. Some of the findings, I think, illustrate how study of such mammalian structures as the baculum, malleus, and hyoid apparatus--structures that seem to be little influenced by the changing external environment--clarifies relationships, if these previously were estimated only from other parts of the anatomy of Recent specimens.

The structural features and characters to be discussed, or listed, below may be arranged in three categories as follows: 1) Characters in which the subgenera Eutamias and Neotamias agree but are different from the genus Tamias; 2) Characters in which the subgenus Eutamias and the genus Tamias agree but are different from the subgenus Neotamias; 3) Structural features that are too weakly expressed to be of taxonomic use.

CHARACTERS IN WHICH THE SUBGENERA EUTAMIAS AND NEOTAMIAS AGREE, BUT DIFFER FROM THE GENUS TAMIAS

Structure of the Malleus.--The malleus in chipmunks is composed of a head and neck, a manubrium which has a spatulate process at the end opposite the head, and a muscular process situated about halfway between the spatulate process and the head of the malleus. An articular facet begins on the manubrium near the neck and spirals halfway around the head of the malleus. A lamina extends from the anterior edge of the head and neck, tapers to a point and joins the tympanic bulla anteriorly where there is a suture between the lamina and bulla. The lamina is one half as long as the rest of the malleus (see figs. 1-3).

Continue reading Genera and Subgenera of Chipmunks free in the Wunder reader →