Late Quaternary vertebrates from the Upper Gunnison Basin, Colorado, and small-mammal community resilience to climate change since the last glacial maximum

Abstract

The Upper Gunnison Basin (UGB), Colorado, is a montane region characterized by unusual physiography and topographic isolation. Excavations of three caves in the UGB provide one of the most diverse records of high-elevation late Quaternary vertebrates in North America. The localities, Haystack Cave (2450 m above sea level [m asl]), Cement Creek Cave (2860 m asl), and Signature Cave (3055 m asl), together provide a near-continuous record of vertebrate communities that extends from before the last glacial maximum to the present. These communities largely represent a sagebrush (Artemisiaspp.) steppe-tundra environment that prevailed throughout the UGB in the late Pleistocene. At least five taxa of extinct large mammals disappear from the UGB by the Early Holocene; one small mammal (the short-faced skunkBrachyprotomacf.B.brevimala) also became extinct. The fossil record further indicates that only four small extant mammals (Sorex preblei,Dicrostonyxsp.,Lemmiscus curtatus, andUrocitellus elegans) were extirpated from the UGB by the Early Holocene, in part because of community restructuring and loss of open habitats with expansion of forests to higher elevations. An analysis of taxonomic richness and evenness at Cement Creek Cave indicates high resilience in the small mammal community despite major climate shifts over the past 40,000+ yr.

Two New Late Quaternary Avifaunas from the East-Central Great Basin with the Description of a New Species of Falco

“…Not surprisingly, all these sites most commonly share numerous species of hawks, falcons, vultures, owls, and sage-grouse. This sagebrush-steppe habitat is further supported by the presence of another sagebrush indicator species, the sagebrush vole ( Lemmiscus curtatus ), which is reported from numerous late Pleistocene cave deposits in western North America (Harris 1985), with additional records now including Haystack (Emslie and Meltzer 2019), Crystal Ball (Heaton 1985), Snake Creek Burial (Bell and Mead 1998), and Smith Creek Cave (Jass 2011).…”

“…Other dates on this species are pre-LGM (∼27,000 cal yrs BP) or late Pleistocene post-LGM (∼12,000 cal yrs BP; Table 1), evincing a persistence of sagebrush habitat in Snake Valley throughout the late Quaternary. Haystack Cave in the Upper Gunnison Basin, Colorado, also produced one bone that might represent the smaller Gunnison Sage-Grouse ( C. minimus ) that provided 2 radiocarbon dates ranging from ∼33,000 to 38,000 cal yrs BP (Emslie and Meltzer 2019). Thus, sagebrush habitat or sagebrush-steppe appears to have dominated valley bottoms in the east-central Great Basin from at least 50,000 years ago to the present.…”

Wildlife visitation at abandoned mines

“…Bones found in caves may indicate occupancy, short-term visitation, accidental entry, or transport by predators or water (Brain 1981, Mondini 1995, Martin and Borrero 1997, Kos 2003. A series of excavations in natural caves near our study site documented nearly 60 species of birds and mammals from the late Quaternary, with a diverse assemblage of 16 species of carnivores including several extinct or locally extirpated species (Emslie and Meltzer 2019). Based on our findings, carnivores and other wildlife appear to have expanded their historical use of natural caves to include abandoned mines.…”

Late Pleistocene Herpetofauna from Two High-Elevation Caves in the Upper Gunnison Basin, Colorado

“…The cave appears to have been used heavily by packrats but also by raptors and by small carnivores (including mustelids) that used it as a den. The recovery of herpetofaunal remains is irregular throughout the various layers, with radiocarbon dates indicating ages from the middle Holocene back to about 46,000 cal yr BP (Emslie and Meltzer 2019). Details and supplementary information about the chronology and vertebrate history from these caves are in Emslie and Meltzer (2019).…”

“…Sites with well-preserved mammalian and herpetofaunal fossils in this region are uncommon, but there are the rare occurrences at the high-elevation localities of Porcupine Cave and Snowmass (Ziegler Reservoir; Barnosky et al 2004, Pigati et al 2014). To enhance the record of the high-elevation vertebrate communities for the southern Rocky Mountains, a series of 3 caves were investigated in the Upper Gunnison Basin (UGB) of southwestern Colorado (Emslie and Meltzer 2019; Fig. 1).…”