Rodents of the Rincon Fauna, Western Chihuahua, Mexico

Abstract

As a result of intensive field work over a number of years, a considerable collection of fossil vertebrates has been obtained by the California Institute of Technology from continental deposits exposed in the drainage basin of the Rio Papigochic in western Chihuahua, Mexico. Quarries in fossiliferous outcrops have been opened in the vicinity of Matachic, Yepomera, and to the north of Yepomera in the general area called the Rincon. A few of the fossil species from these deposits have been described, but the bulk of the material is only now being studied in detail. Among the former may be mentioned a leporid, Notolagus velox (Wilson, 1937); a badger, Taxidea mexicana (Drescher, 1939); and an antilocaprid, Hexobelomeryx fricki (Furlong, 1941). The relative ages of the various quarry sites have not been determined in detail, but the fauna is of Hemphillian age, probably late in this interval. Because earlier papers referred to the described forms as from Rincon, a rather broad geographic area, the writer continues to do so in the sense of a general Rincon fauna which may involve local faunas of perhaps slightly different ages. Fossil rodent material from the Rincon area is relatively scarce, and at present consists exclusively of ground-dwelling sciurid types. This rodent group, however, is represented by a number of species, perhaps five in all, and compares very favorably in diversity with present-day sciurid faunas from local areas. Two of the types are giants in their respective genera, and a third type is represented by unusually complete material. The remaining two are not given specific assignments, for it is hoped that additional collecting will serve to determine their relationships more clearly than can be done at present. The photographs, with the exception of those in plate 1, have been retouched by Mr. David P. Willoughby, scientific illustrator of the Division of the Geological Sciences, California Institute of Technology. Plate I was made up a number of years ago by Mr. John L. Ridgway, onetime illustrator for the same institution. My thanks are due to Dr. Remington Kellogg, Curator of Mammals, U. S. National Museum, for the loan of Recent Citellus material from that institution. The present paper was prepared during the writer's tenure as National Research Fellow in paleontology.