Louis H Taylor

Denver Museum of Nature and Science

Porcupine Cave, arguably the richest source of information in the world on Irvingtonian-age vertebrates, sits in the Colorado Rocky Mountains at 2900 m (latitude 38°43'45" N, longitude 105°51'41" W, USGS Gribbles Park 7.5' Quad) (figures 2.1, 2.2). Situated on the southwest rim of the highest large intermountain basin in North America, known as South Park, the cave is a three-tiered chamber comprising at least 600 m of passageways (figures 2.3-2.7). South Park itself lies nearly in the center of Colorado (figure 2.1) and hosts diverse biotic communities, some of which are unique in the lower 48 United States for their vegetational affinity to central Asia. Although humans have utilized various resources in South Park for centuries, the basin remains sparsely populated, with a wide variety of non-human-dominated landscapes still intact.

The entrance to Porcupine Cave overlooks a west-facing slope that is near the ecotone between Festucca-Muhlenbergia grassland, Pinus-Pseudotsuga needleleaf forest, and Picea-Abies needleleaf forest (Küchler, 1964). Vegetation outside the entrance consists of sparse stands of Pinus ponderosa (Ponderosa pine), Pinus edulis (pinyon pine), Pseudotsuga men-ziesii (Douglas-fir), and Juniperus (juniper) interspersed with Artemisia (sagebrush), Chrysothamnus (rabbitbrush), Cercocar-pus (mountain mahogany), Yucca (Spanish bayonet or soap-weed), Coryphantha (cactus), Opuntia (prickly pear), grasses, and other small herbaceous plants (Barnosky and Rasmussen, 1988:269). The existing entrance is through a mine adit. Before emplacement of the adit (most likely in the 1870s), animals would have had to enter the cave through various cracks and fissures that were probably intermittently open and closed.

Since 1985, when the first systematic paleontological excavations took place at the site, crews from the Carnegie Mu seum of Natural History, the Denver Museum of Nature and Science (previously called the Denver Museum of Natural History), and the University of California Museum of Paleontology have discovered new localities within Porcupine Cave nearly every year. Chapter 4 chronicles the excavation history. Fifteen years of field work at the cave have yielded at least 26 different fossil localities. These localities sample a wide variety of Quaternary and potentially latest Tertiary time periods, and to some extent varying taphonomic situations. This chapter documents the spatial distribution of the many different collecting localities and provides an overview of their suspected geological ages and general taphonomic settings. More details on geological age and correlation are provided in chapters 6 and 7 and in Bell and Barnosky (2000). Older publications on Porcupine Cave (Barnosky and Rasmussen, 1988; Wood and Barnosky, 1994; Barnosky et al., 1996) proposed a somewhat younger age for some of the strata than is now believed to be the case (see discussion of the Pit locality below).

Other important Irvingtonian vertebrate paleontological sites from the central Rocky Mountain region include the Hansen Bluff sequence in the San Luis Valley, Colorado (Rogers et al., 1985, 1992) and the SAM Cave deposits in north-central New Mexico (Rogers et al., 2000). These sites are of particular interest in yielding paleomagnetic, radiometric, palynologi-cal, and invertebrate paleontological data associated with the fossil vertebrates (Rogers et al., 1985, 1992, 2000; Rogers and Wang, 2002). Specimens of vertebrate fossils and numbers of species are sparse from Hansen Bluff (Rogers et al., 1985, 1992) and moderate in abundance at SAM Cave, with the latter including 2 species of amphibians, 3 of reptiles, approximately 10 of birds, and approximately 30 of mammals, distributed through 14 collecting localities (Rogers et al., 2000).

FIGURE 2.1 Location of Porcupine Cave.

Degrees West Longitude

FIGURE 2.1 Location of Porcupine Cave.

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