REFERRED MATERIAL Velvet Room: DMNH 33949 fragmentary R jaw with alveoli pl-4 (G 0, 5, 6, 7, L30); 34570 R Ml (G 0, 5, 6, 7, L 30). Mark's Sink: 34569 fragmentary R maxilla with P4 (8/96); 36681 L jaw with alveoli c-ml (L19, 7/97); 39563 fragmentary L Ml (124, 7/97); 40243 R c (8/96); 40244 R C (8/96); 40266 R c (L22, 7/97). Ferret Room: DMNH 2277l skull fragments. Generator Dome: DMNH L c (Ll). Gypsum Room: CM 48439 L ml.
DESCRIPTION AND COMMENTS Two diagnostic teeth, P4 and Ml, of a true marten (subgenus Martes) were identified in l996 from Mark's Sink and the Velvet Room, respectively (Anderson, l997). Since then, several additional specimens including an ml have been found. This material represents the oldest Pleistocene marten in North America. In size and morphology (figure l3.l), the specimens are similar to those of M. americana, the extant American marten. The P4 (DMNH 34569) lacks an external median rootlet, which is characteristic of the subgenus Pekania (fishers); the Mls (DMNH 34570 and 39563) show the characteristic expansion of the inner lobe; and the ml has a small, distinct metaconid and a basined talonid. A preserved parietal (DMNH 2277l) shows the broad tabletlike band bordered by two faint lines, the temporal ridges, which distinguish a young adult marten (in adults the ridges unite to form the sagittal crest).
In his genetic study of M. zibellina, the sable, and M. americana, Hicks (l996) showed that the two species are not closely related, as had formerly been thought (Anderson, l994), and that the American marten has had a long, independent history in North America. The discovery of a true marten at Porcupine Cave confirms his conclusions.
MUSTELA FRENATA LICHTENSTEIN, 1831
DESCRIPTION AND COMMENTS Fossils of long-tailed weasels are common in Porcupine Cave, especially in the Velvet Room (33 specimens) and Mark's Sink (39 specimens). Other Irvingtonian records of M. frenata include Conard Fissure, Arkansas, and Leisey Shell Pit, Florida, and the species has been recognized in 45 late Rancholabrean faunas ranging from California to Florida and south to Nuevo Léon, Mexico. Today the long-tailed weasel has the broadest geographic range of any American weasel, and its wide ecological tolerances enable it to inhabit plains, brushy areas, open woodlands, coniferous forests, and alpine regions. Specimens from Porcu-
pine Cave are indistinguishable in size and morphology from other Pleistocene and Recent samples.
MUSTELA ERMINEA LINNAEUS, 1858
description and comments Mustela erminea is the smallest extant mustelid in Colorado. Although there can be some overlap in measurements between female M. frenata and male M erminea, this was not a problem in the Porcupine Cave specimens. In the Velvet Room, remains of M. erminea (27 specimens) and M. frenata (33 specimens) are both common and are found together in several grids and levels (Gl, L8; G8/8A, L2; G8/8A, L3; Gl2, L5; Gl6, L3). In contrast, in Mark's Sink, remains of M. frenata outnumber those of M. erminea 39 to ll. Whether this situation is an artifact of collecting or deposition, or reflects ecological conditions less favorable to ermine, is unknown.
Mustela erminea has been recognized at Cudahy, Kansas, and Conard Fissure, Arkansas, both Irvingtonian in age, and from 20 late Rancholabrean faunas. In Colorado the species currently ranges from the foothills to the tundra in timbered areas.
MUSTELA NIGRIPES (AUDUBON AND BACHMAN, 1851)
DESCRIPTION AND COMMENTS Anderson (1996) reported the first Irvingtonian record of Mustela nigripes, four specimens from the Velvet Room (figure 13.2) and the Pit in Porcupine Cave. Since then, an additional 12 specimens have been identified, including postcranial elements. Compared with M. vison, the American mink, M. nigripes is characterized by auditory bullae that are more inflated, a smaller infraorbital foramen, a thicker mandible, relatively larger canines, an m1 that lacks a metaconid, and a smaller m2. Ferret post-cranial elements are heavier and more rugose than those of mink. The specimens from the cave are nearly identical in size and morphology to recent samples.
Mustela nigripes and their preferred prey, Cynomys spp. (prairie dogs), have been found in the Badger Room, Velvet Room, Mark's Sink, Will's Hole, and the Pit. So far, ferrets have not been found in Generator Dome. The only other Irving-tonian site with M. nigripes is Cathedral Cave, Nevada (J. I. Mead, pers. comm., 1998).
MUSTELA VISON SCHREBER, 1777
DESCRIPTION AND COMMENTS In 1994 Mustela vison was identified in Porcupine Cave, and the species is now rep resented by 16 specimens recovered from the Velvet Room, Mark's Sink, Will's Hole, and the Ferret Room (figure 13.3). Compared with those of Mustela nigripes, crania of M. vison have a larger inner lobe on M1, a larger infraorbital foramen, a wider occipital region, less inflated auditory bullae, an incipient metaconid and a wider talonid on m1, and a much larger m2. The postcranial skeleton of M. vison is less rugose than that of M. nigripes.
As Kurten and Anderson (1980) noted, the fossil history of M. vison extends back to the Irvingtonian (Cumberland Cave, Conard Fissure, Cudahy, and now Porcupine Cave). The species has been recognized in 30 late Rancholabrean faunas. In Colorado M. vison currently has a wide distribution from the plains to above 3000 m, but the species is nowhere abundant (Armstrong, 1972). Semiaquatic in habits, mink den along stream banks and feed on riparian animals. The presence of M. vison in a fauna indicates the nearby presence of permanent water, and thus the species is an important environmental indicator.
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