Cranial and Bacular ' Variation in Populations of Spiny Rats of the Genus Proechimys (Rodentia: Echimyidae) * Mm South America
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ROBERT E. MART Cranial and Bacular ' Variation in Populations of Spiny Rats of the Genus Proechimys (Rodentia: Echimyidae) * mm South America SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • 1970 NUMBER35 SERIAL PUBLICATIONS OF THE SMITHSONIAN INSTITUTION The emphasis upon publications as a means of diffusing knowledge was expressed by the first Secretary of the Smithsonian Institution. In his formal plan for the Insti- tution, Joseph Henry articulated a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge not strictly professional." This keynote of basic research has been adhered to over the years in the issuance of thousands of titles in serial publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Annals of Flight Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to ^oology Smithsonian Studies in History and Technology In these series, the Institution publishes original articles and monographs dealing with the research and collections of its several museums and offices and of professional colleagues at other institutions of learning. These papers report newly acquired facts, synoptic interpretations of data, or original theory in specialized fields. Each publica- tion is distributed by mailing lists to libraries, laboratories, institutes, and interested specialists throughout the world. Individual copies may be obtained from the Smith- sonian Institution Press as long as stocks are available. S. DILLON RIPLEY Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY NUMBER 35 Robert E. Martin Cranial and Bacular Variation in Populations of Spiny Rats of the Genus Proechimys (Rodentia: Echimyidae) from South America SMITHSONIAN INSTITUTION PRESS CITY OF WASHINGTON I97O ABSTRACT Martin, Robert E. Cranial and Bacular Variation in Populations of Spiny Rats of the Genus Proechimys (Rodentia: Echimyidae) from South America. Smithsonian Contributions to Zoology, 35:1-19. 1970.—Specimens of Proechimys from 12 local- ities in Bolivia, Brazil, Colombia, and Peru, were studied to assess the degree of variation in bacular, cranial, and dental morphology, and pelage. Coefficients of variation and Student's t values were computed for selected cranial measurements to evaluate intra- and interpopulation variation. Studies on tooth wear demonstrated considerable variation in dental occlusal pattern and suggested that taxonomic assignment based entirely on dental morphology may be misleading. Descriptions and illustrations of bacula from most localities indicate that these bones are highly variable in overall dimensions, but have common structural features at a particular locality. Most specimens are tentatively referred to Proechimys guyannensis, although P. cani- colUs, P. quadruplicates, and P. steerei were also represented. Proechimys guyannensis is regarded as a highly variable species. It is suggested that subspecific delimitation may not adequately express the variation observable in this species. Official publication date is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1&70 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover) Robert E. Martin Cranial and Bacular Variation in Populations of Spiny Rats of the Genus Proechimys (Rodentia: Echimyidae) from South America Introduction relate these data with the results of analyses of cranial, bacular, dental, and pelage morphology. Taxonomic Spiny rats of the genus Proechimys are caviomorph assignment was only a secondary objective. Descrip- rodents of the family Echimyidae inhabiting most tions were written of the morphological features com- forested areas of South America north of the Tropic mon to specimens from each locality, and compari- of Capricorn and Central America northward to Nica- sons made with other populations. The accounts ragua (Moojen, 1948). Although these rats frequently reflect differences between populations from different live near streams, they are not entirely riparian and localities, and offer suggestions on taxonomic assign- may inhabit semiarid grasslands (Hershkovitz, 1948) ment, but are not taxonomic descriptions in the strict or dry forests (Allen, 1904). sense. All specimens examined are deposited in the The wide range of morphological variation observed mammal collection of the National Museum of Nat- in these rats has made species determination difficult. ural History. This has caused problems in the taxonomy of the genus I wish to express my sincere appreciation to the in- (see Thomas, 1927, 1928a, 1928b; Hershkovitz, 1948; dividuals who aided in the completion of this report. and Moojen, 1948). Thomas (1928a, p. 262) re- Dr. Gary L. Ranck, formerly Curator of the Mammal marked that "The bewildering instability of the char- Identification Service, Smithsonian Institution, di- acters of these spiny rats makes it at present impos- rected the study and offered helpful advice and criti- sible to sort them according to locality into separate cism. Dr. Henry W. Setzer, Associate Curator, Division species, subspecies, or local races." of Mammals, Smithsonian Institution, aided in the The present study is an effort to measure some ele- statistical treatment of the data. Dr. Ronald H. Pine, ments of variation in Proechimys, and thereby provide Curator, Mammal Identification Service, reviewed the an aid toward future taxonomic work in the genus. manuscript and sent specimens for additional study. Initially, the most useful measurements were selected Dr. Charles O. Handley, Jr., Curator-in-Charge, and by a study of variation within a population. The pri- Dr. David H. Johnson, Research Curator, Division of mary aims were to: (1) assess interpopulation varia- Mammals, gave useful advice. Dr. George E. Watson, tion in cranial dimensions; and (2) attempt to cor- Chairman, and other personnel of the Department of Vertebrate Zoology, Smithsonian Institution, provided Martin, Robert E., Department of Biology, Texas Tech University, Lubbock, Texas 79409. helpful comments on the manuscript. Dr. Merle L. 1 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY Kuns and associates of the Middle America Research to Patterson and Pascual (1968) this assemblage, in- Unit collected most of the specimens analyzed. cluding Paradelphomys and Xylechimys, represents the At Oklahoma State University, Dr. Bryan P. Glass, subfamily Adelphomyinae. Professor of Zoology, served as major advisor and The earliest fossil forms of Proechimys are of late critically read the manuscript. Dr. Herbert L. Bru- Pleistocene or Recent age and thus shed no light on the neau, Associate Professor of Zoology, and Dr. Wil- early history of the genus. Moojen (1948) suggested liam A. Drew, Associate Professor of Entomology, that evolutionary development in Proechimys has been served on the graduate advisory committee and read directed toward species with increased numbers of the manuscript. Dr. George A. Moore, Professor counterfolds in the cheek teeth. For evidence, Moojen Emeritus of Zoology, gave advice and critically read mentioned the low counterfold numbers in the cheek the manuscript. At Texas Tech University Dr. teeth of fossil Proechimys from Lagoa Santa, Brazil, Robert L. Packard, Professor of Biology, and Mr. and like numbers in the teeth of species in the subgenus Tony R. Mollhagen, provided helpful advice on the Trinomys. An increased number of counterfolds along manuscript. with greater species diversity is present in the subgenus Mr. Paul Ryan took the photographs that aided in Proechimys, and may be an indication that the multi- the preparation of Figure 3. My wife, Patricia, helped counterfold line of spiny rats is more "successful" in an by recording data and preparing most of the illustra- evolutionary sense. Convincing evidence, however, is tions. Mrs. Frank Roberts and Mrs. Daniel Carabine definitely lacking on this point. typed final stages of the manuscript. The name Proechimys was proposed by Allen This report is based on a research project con- (1899b) using Echimys trinitatis Allen and Chapman, ducted in 1967 while the author was a summer as the genotype. His concept of the genus included spe- research assistant in the Division of Mammals, Smith- cies of Hoplomys and Mesomys, presently accorded full sonian Institution, Washington, D.C. Financial aid generic rank in the family Echimyidae. Thomas (1921) during this period was provided by a stipend from the proposed the subgenus Trinomys to characterize the Office of Education and Training, Smithsonian In- spiny rats of southeastern Brazil that have a distinctive stitution. The paper that resulted from that study was mainfold arrangement in the cheek teeth. Tate (1935) submitted to the Graduate College of Oklahoma State presented a taxonomic history of the genus Proechimys, University in partial fulfillment of the requirements for later supplemented by Ellerman (1940), Hershkovitz the degree of Master of Science in Zoology. (1948), Moojen (1948), and Cabrera (1961). Most of the discussion