قراءة كتاب Pleistocene Pocket Gophers From San Josecito Cave, Nuevo Leon, Mexico
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Pleistocene Pocket Gophers From San Josecito Cave, Nuevo Leon, Mexico
the cave. Jakway (1958:313-327) has reported on the lagomorphs and rodents in detail, and compared this part of the cave fauna with that of Rancho La Brea and Papago Spring Cave, Arizona. Jakway (lit. cit.:323-324) suggests that the fauna from San Josecito is late Pleistocene, probably contemporaneous with the remains from Papago Spring Cave and pre-Rancholabrean.
I thank Professor E. Raymond Hall and Dr. Robert W. Wilson for their permission to examine this material and for critical comments and advice on the manuscript. The drawings were made by Miss Lucy Remple. The specimens are a part of the collection of fossil vertebrates formerly belonging to the California Institute of Technology, but now the property of the Los Angeles County Museum. The specimens had been lent by the late Professor Chester Stock to Professor Hall and Dr. Wilson for study and report. All measurements herein are in millimeters.
Material referable to Thomomys consists of a nearly complete cranium, L.A.C.M. (C.I.T.) No. 3952, with nasals, maxillary teeth, and lower parts of braincase missing and zygomata broken; four rami (unnumbered), one of which is badly broken; and two isolated molariform teeth. The skull has a sphenoidal fissure, a feature typical of the umbrinus group of Thomomys. The fossil specimens closely approximate in size the living subspecies Thomomys umbrinus analogus Goldman. Thomomys is not known from the vicinity of the cave at the present time and has not been reported from southwestern Nuevo León, even though there has been extensive collecting for pocket gophers there in recent years. To my knowledge the nearest record of occurrence of modern Thomomys is a series of Thomomys umbrinus analogus from 12 miles east of San Antonio de las Alazanas at an elevation of 9000 feet in the state of Coahuila (Baker, 1953:511), approximately 85 miles to the northwest. The fossil gophers are not from the talus of the cave floor, which is evidently of subrecent origin, but from the Pleistocene deposits below. Close resemblance to the living subspecies T. u. analogus, however, indicates that these remains are not so old as some of the other geomyid fossils from the cave.
Seven rami pertain to the genus Cratogeomys. All except three, L.A.C.M. (C.I.T.) Nos. 2974, 2978, and 3954, lack cheek teeth and the posterior processes are missing on most of the mandibles. No. 2974 is smaller than the other specimens, and probably is from a young individual. No. 3954 may have been fossilized at an earlier date than the other six jaws; however, it is comparable to them in size and morphology. Also present in the deposits are three limb bones of Cratogeomys castanops. One, a right humerus bearing L.A.C.M. (C.I.T.) No. 2982, is slightly larger than that of the pocket gophers living in the area now. Two tibias, L.A.C.M. (C.I.T.) Nos. 2983 and 2984, complete the material referable to this species.
Cratogeomys castanops planifrons (see Russell and Baker, 1955:607) occurs in the immediate vicinity of San Josecito today. None of the rami from the cave differs appreciably from those of the subnubilus group of Cratogeomys castanops, a group of small subspecies including planifrons, subnubilus, rubellus and peridoneus. All are small in external measurements and skull and differ markedly in this respect from the group of large subspecies (the subsimus group) that occurs farther northward in Coahuila and Nuevo León.
A rostral part of a skull, L.A.C.M. (C.I.T.) No. 2927, is referable to the genus Cratogeomys. This fragment consists of the anterior part of the skull, including a portion of the frontals,
