CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY THE UNIVERSITY OF MICHIGAN VOL. 23, NO. 1, p. 1-36 (13 text-figs.) NOVEMBER28, 1969 THE RODENTS FROM THE HAGERMAN LOCAL FAUNA, UPPER PLIOCENE OF IDAHO BY RICHARD J. ZAKRZEWSKI Idaho State University MUSEUM OF PALEONTOLOGY THE UNIVERSITY OF MICHIGAN ANN ARBOR CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY Director: ROBERTV. KESLING The series of contributions from the Museum of Palentology is a medium for the publication of papers based chiefly upon the collection in the Museum. When the number of pages issued is sufficient to make a volume, a title page and a table of contents will be sent to libraries on the mailing list, and to individuals upon request. A list of separate papers may also be obtained. Correspondence should be directed to the Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan 48104. VOLS. 2-22. Parts of volumes may be obtained if available. Price lists available upon inquiry. THE RODENTS FROM THE HAGERMAN LOCAL FAUNA, UPPER PLIOCENE OF IDAHO1 RICHARD J. ZAKRZEWSKI" Idaho State University ABSTRACT-The Hagerman local fauna is known from deposits of the Glenns Ferry Formation exposed west of the town of Hagerman in Twin Falls County, Idaho. Approximately 300 localities are known over an area of six square miles through 500 feet of beds (elevation 2900 to 3400 feet above sea level). Rodents are represented in the fauna by at least 14 genera and 19 species. These include five species from the family Sciuridae, two from the Geomyidae, three from the Heteromyidae, two from the Castoridae, and seven from the Cricetidae. Five of the species are described as new: Pliogeomys parvus, Perognathus magnus, P. maldei, Dipoides intermedius, and Baiomys aquilonius. The beaver Castor and the microtines Cosomys and Pliopotamys are the most abundant mammalian forms in the fauna. This fact suggests a marsh-meadow habitat near the deposi- tional area. Upland forms, though rare in the fauna, become relatively more abundant above 3100 feet. Changes in the population structure of the microtines are demonstrated as one goes higher in the section. These changes include a slight increase in size for Cosomys and Plio- potamys and an increase in the number of triangles on the MI in Cosomys and Ophiomys. There is also a gradual replacement of Cosomys by Pliopotamys and Ophiomys, which appar- ently becomes complete above the elevation of 3265 feet. On the basis of the fauna and a potassium-argon date of 3.48 t 0.27 X 10' years on a basalt which has been correlated with the basalt approximately 150 feet below the Horse Quarry, the Hagerman local fauna is considered to be Upper Pliocene in age. Comparison with other Upper Pliocene local faunas in regard to the stage of evolution of the rodents suggests a post-Rexroad age for the Hagerman local fauna. CONTENTS Introduction ............................................................................................................................................................................... 1 Previous work ........................................................................................................................................................................... 2 Materials and methods ........................................................................................................................................................... 2 Systematic paleontology ........................................................................................................................................................ 4 Family Sciuridae ...............................................................................................................................................................4 Family Geomyidae ........................................................................................................................................................... 7 Family Heteromyidae ....................................................................................................................................................... 11 Family Castoridae. ............................................................................................................................................................. 13 Family Cr~cetldae............................................................................................................................................................. 16 Conclusions ................................................................................................................................................................................. 27 Paleoecology ....................................................................................................................................................................... 27 Age and correlation ......................................................................................................................................................... 31 Acknowledgments ..................................................................................................................................................................... 34 Literature cited ......................................................................................................................................................................... 34 INTRODUCTION fossil finds to warrant a field party from the United States National Museum. The party The Hagerman local fauna is opened the now world famous Horse Quarry flood plain and stream deposits of the Glenns (Gazin, 1936). Ferry Formation (Malde & Powers, 19b2) ex- The fauna has been considered as one of posed west of the town of Hagerman in Twin the classic Upper Pliocene faunas of North Falls County, 1daho. Approximately 300 local- America and was thought to be well known. ities are known over an area of six square miles However, collections of fossils by field parties through 500 feet of beds. The fauna has been from The University of Michigan, Museum of known since the late 1920's when Elmer Cook, PaIeontology, under Claude W. Hibbard in the a local rancher, created enough interest in his summers of 1956, 1962, 1964-1966, and by ' This paper is a revision of the thesis submitted in a partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan. 'President's Postdoctoral Fellow in Geology. 2 RICHARD J. ZAKRZEWSKI Philip R. Bjork and Richard J. Zakrzewski in principally on personal communication with 1967 have more than doubled the fauna. The Hibbard. The most recent study involved the presence of radiometrically dated horizons, the microtine genus Ophiomys (Hibbard & Zakr- best of which is a basalt dated at 3.48 + 0.27 zewski, 1967). X lo6 years which has been correlated with the basalt 150 feet below the Horse Ouarrv (Evern- MATERIALS AND METHODS den, et al., 1964) has placed the ~agerman The materials discussed in this report con- local fauna in a critical position for the inter- sist of maxillaries and jaws, with and without pretation of late Cenozoic history. teeth, plus numerous isolated teeth of rodents Of great importance in placing the Hager- from the Hagerman local fauna. Post-cranial man local fauna in its proper perspective is the material was considered only in the discussion rodent portion of the fauna. Rodents, especially of Paenemarmota and Dipoides. Measurements microtines, are very abundant throughout the were made to the nearest 0.01 mm, using a section. Because of the rapid evolution which Gaertner Measuring Microscope. Statistical microtines have undergone (Zakrzewski, 1967) analyses were made using The University of they are valuable for correlative purposes. The Michigan IBM 7090 computer. microtines, as well as the other rodents, are The specimens are listed under the various limited in their habitat preferences and are, taxa, except in the case of Citellus cf. C. therefore, good indicators of the ecology. hozelelli, Thomomys, and the microtines, which Changes in the population structure of the are too numerous to list individually. The term- microtines have also been demonstrated (Hib- inology used in the discussion of the various bard, 1959 ; Hibbard & Zakrzewski, 1967). The groups is defined under the specific group in combination of these factors makes the study question. The majority of the specimens are in of the rodents of great interest. the collection of The Universitv of Michigan. Museum of Paleontology. The others are tibe PREVIOUS WORK found in the United States National Museum. The first description of rodents from the The specimens found in the former are pre- Hagerman local fauna was by Wilson (1933). fixed by a V; those in the latter by USNM. He also described and discussed rodents from Recent forms used for comparison are in The the younger Grand View local fauna. From the University of Michigan, Museum of Zoology Hagerman local fauna he described Citellus ? (UMMZ) . sp., Thomomys gidleyi, Mimomys (Cosomys) The specimens and the localities at which primus, and Ondatra idahoensis minor. Wilson they are found are listed in stratigraphic order. (1933) discussed the beaver from the Grand This is not necessarily in topographic order, as View local fauna and questionably placed the Bjork (pers. comm.) has demonstrated a ver- Hagerman beaver in the same species. Stirton tical displacement of 160 feet between some of ( 1935) after cursory examination referred the the marker horizons in the Glenns Ferry For- beaver to another