DENVER MUSEUM OF NATURE & SCIENCE ANNALS DENVER MUSEUMDENVER OF NATURE & SCIENCE ANNALS • NUMBER 8 DECEMBER 23, 2019 DENVER MUSEUM OF NATURE & SCIENCE ANNALS NUMBER 8, DECEMBER 23, 2019

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Cover photo: Denver Museum of Nature and Science Curator of Paleoecology Dr. Richard Stucky and students from the 2011 Teen Science Scholars program excavating mammoth bones at Locality 4086 of the Villa Grove Paleontological Site. From left to right: Emily Hoefs; Olivia Verma; Evan Alger-Meyer; Richard Stucky; Ashley Goodfellow; Clara Miller; Orion Hunter. Photo: Steven Holen, July 14, 2011.

The Denver Museum of Nature & Science Annals is an Frank Krell, PhD, Editor-in-Chief The Pleistocene Mammalian Fauna open-access, peer-reviewed scientifi c journal publishing and Paleoenvironment of the EDITORIAL BOARD: original papers in the fi elds of anthropology, geology, James Hagadorn, PhD (subject editor, Paleontology and paleontology, botany, zoology, space and planetary Villa Grove Paleontological Site, Geology) sciences, and health sciences. Papers are either authored Colorado Nicole Garneau, PhD (subject editor, Health Sciences) by DMNS staff, associates, or volunteers, deal with DMNS John Demboski, PhD (subject editor, Vertebrate Zoology) specimens or holdings, or have a regional focus on the Steve Lee, PhD (subject editor, Space Sciences) Rocky Mountains/Great Plains ecoregions. Evan Alger-Meyer, Frank Krell, PhD (subject editor, Invertebrate Zoology) Jared Maxwell Beeton, The journal is available online at www.dmns.org/science/ Steve Nash, PhD (subject editor, Anthropology and Richard K. Stucky, and publications/dmns-annals free of charge. Paper copies are Archaeology) Steven R. Holen available for purchase from our print-on-demand publisher

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The Pleistocene Mammalian Fauna and 1 Evan Alger-Meyer Paleoenvironment of the Villa Grove Jared Maxwell Beeton2 Richard K. Stucky3 Paleontological Site, Colorado Steven R. Holen4

ABSTRACT—Excavations of a gravel pit in 2011 and 2012 near the town of Villa Grove in the San Luis Valley of Colorado yielded several Pleis- tocene megafauna and small mammal fossils. We describe and analyze the fauna from the site and illustrate how this assemblage provides insights into Colorado high-altitude basin ecosystems during the Late 1Department of Earth Sciences, Denver Pleistocene. Extant taxa from the site include Brachylagus idahoensis, Museum of Nature & Science, 2001 Cynomys cf. gunnisoni, Lemmiscus curtatus, Lepus sp., cf. Sylvilagus Colorado Boulevard, Denver, Colorado nuttallii, and Urocitellus sp. Extinct taxa recovered include Camelops 80205-5798, U.S.A. sp., Canis dirus, Equus cf. conversidens, and Mammuthus columbi. [email protected] An unidentified species of Bison likely constitutes an extinct species, and Brachylagus idahoensis and Canis dirus are the first fossil occurrences 2Department of Environment and of these taxa in Colorado. The genera Brachylagus, Lemmiscus, and Sustainability, Fort Lewis College,1000 Urocitellus are currently found in northern Colorado but not in the San Rim Drive, Durango, Colorado 81301, Luis Valley. The fossil assemblage suggests that a sagebrush-prevalent U.S.A. plains environment persisted in this region during the Wisconsinan [email protected] glaciation, possibly comparable to that of the Great Basin.

3Department of Earth Sciences, Denver Museum of Nature & Science, 2001 Colorado Boulevard, Denver, Colorado 80205-5798, U.S.A. [email protected]

4Center for American Paleolithic Research, 27930 Cascade Road, Hot Springs, South Dakota 57747, U.S.A. [email protected] Alger-Meyer, Beeton, Stucky, Holen

The end of the Pleistocene marked a transition from (Hager 1975), Porcupine Cave (1 million to 780,000 the Last Glacial Maximum and the glacial–interglacial- years BP) (Barnosky 2004), and the more recent Weis dominated global climate of the past few million years Gravel Pit Stegomastodon Site (1.2 million years BP) to the warmer and more stable Holocene. This climatic (Meade-Hunter et al. 2012). Material from the middle shift had substantial impacts on ecosystems worldwide, Pleistocene of Colorado is poorly known outside of the some of which continue into the present (Graham et Ziegler Reservoir Fossil Site, which contains deposits al. 1996, Blois & Hadley 2009). Assessing the effect of spanning the end of the middle Pleistocene through climate change and ecosystem alteration in the fossil the early part of the Late Pleistocene (140,000–77,000 record can allow us to understand more fully trends years BP). The remaining, large Colorado Pleistocene in the distributions of modern taxa, and predict how sites are generally Late Pleistocene in age. Cement they are likely to respond to future climatic shifts. It is Creek Cave contains late-Pleistocene fossils deposited therefore important to document a reliable, consistent from 49,800 ± 3,800 years BP to 1,120 ± 40 years BP record of fossil faunas, particularly for sites preceding to the present (Reynard et al. 2015). The Lamb Spring the Pleistocene–Holocene transition. Archaeological Preserve Site represents deposition from Megafaunal extinctions characterized vertebrate 17,850 ± 550 years BP to 14,500 ± 500 years BP (Elias community changes throughout North America during & Toolin 1990), the Selby and Dutton archaeological the Late Pleistocene and through the Pleistocene– localities represent deposition from 13,600 ± 485 to Holocene transition (Faith & Surovell 2009). Smaller 11,710 ± 150 years BP (Stanford & Graham 1985, Holen changes in microvertebrate communities were also 2006), and the Haystack Cave specimens were deposited common and complex (Graham et al. 1996, Schmitt & from 14,935 ± 610 to 12,154 ± 1,700 years BP (Emslie Lupo 2012, 2016). Pleistocene fossil sites are distributed 1986). Individual specimens and smaller sites include throughout North America, with those in California those from the Magna Site, Fairplay locality, Florissant and Florida among the most well-known (Stock 1956, locality, Zapata Mammoth Site, Medano Mammoth Site, Morgan 2002). Sites from the Rocky Mountains and and Alamosa National Wildlife Refuge Sites, among surrounding areas are generally less well studied, others (Wescott et al. 2016, also see review in Murphy et but include important records of biodiversity, such as al. 2015). Of these localities, the Ziegler Reservoir Fossil those from Porcupine Cave, Natural Trap Cave, and the Site, Hansen Bluff Site, Porcupine Cave, Cement Creek Ziegler Reservoir Fossil Site (Martin & Gilbert 1978, Cave, Haystack Cave, Magna Site, Fairplay Site, Floris- Barnosky 2004, Miller et al. 2014, Sertich et al. 2014). sant Site, Zapata Mammoth Site, Medano Mammoth High-elevation paleontological sites are of great inter- Site, and Alamosa National Wildlife Refuge Sites are est because they document more climatically variable found at elevations higher than 2,200 m (Emslie 1986, ecosystems and are less common than lower elevation Elias & Nelson 1989, Rogers et al. 1992, Barnosky 2004, sites (Miller et al. 2014, Sertich et al. 2014). Miller et al. 2014, Sertich et al. 2014, Reynard et al. Pleistocene vertebrate fossil sites have been docu- 2015, Wescott et al. 2016, and also see review in Murphy mented in Colorado for more than one hundred years et al. 2015). and include hundreds of localities (see the review in The Villa Grove Paleontological Site (VGPS) Murphy et al. 2015). Most of these sites contain isolated is a fossiliferous late-Pleistocene gravel pit from the remains scattered throughout the state, although several northern San Luis Valley (Fig. 1) with sediments and more substantial sites have been studied as well. mammoth dentin dated to between 25,600 ± 80 14C Major early-Pleistocene sites from Colorado years BP and 33,405 ± 340 14C years BP. It is a smaller include the Hansen Bluff Site [2.67 million to 670,000 high-elevation site (~2,430 m) that contains several years before present (BP)] (Elias & Nelson 1989), the mammalian megafaunal and microvertebrate remains. Donnelly Ranch Vertebrate Site (2.5 million years BP) It stands out as a site of somewhat unique age for

2 DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 Villa Grove Paleontological Site Fossils and Paleoenvironment

Materials and Methods The geological context of the VGPS was determined based on soil stratigraphic data such as soil sediment color, texture, structure, mineralogy, carbonate mineralogy, boundary characteristics, horizonation, and depositional environment. Sediments and soils are described using standard procedures and terminology outlined by the Soil Survey Division Staff (1993) and Birkeland (1999). Organic materials and bones were collected and sent out for radiocarbon dating to establish temporal control. Further lab work included sediment size analysis using the hydrometer method and organic carbon percentage determination using loss on ignition. Fossil specimens under study were recovered in July 2011, August 2011, and July 2012 by staff from the Denver Museum of Nature & Science (DMNS) and the Colorado Bureau of Land Management. Larger materials were jacketed with plaster or foil in the field whereas smaller specimens were sifted out using 1-mm sieves onsite. Sedi- ment samples brought back to the lab were picked and yielded no additional fossils. Specimens DMNH EPV.62800, DMNH EPV.63766, DMNH EPV.63755, and DMNH EPV.63747 were prepared by DMNS paleontology labora- Figure 1. Location of Villa Grove, near the tory staff. Measurements of the smaller specimens were Villa Grove Paleontological Site, and the two made using 6-inch dial calipers calibrated to 0.005 mm. localities from which fossils were collected Measurements were taken according to the median points (DMNH locality 4085 and DMNH locality of the element, such as from the buccal to lingual or pos- 4086). Site relative to the state of Colorado (A) terior to anterior edge of a tooth, unless otherwise stated. and the northern San Luis Valley area (B). Fossils were identified using comparative specimens from the DMNS Zoology and Earth Sciences Collections, as well Colorado, documenting slightly younger late-Pleistocene as specimens from the Berkeley Museum of Vertebrate faunas than Cement Creek Cave and older faunas than Zoology, and guidelines for identification described in the Lamb Spring Archaeological Preserve Site, the Selby relevant literature (described later). and Dutton localities, and Haystack Cave. The faunal The site itself is designated by two primary localities: composition is also of note as the presence of two DMNH locality 4085 and 4086. Locality 4085 is situated sagebrush-dependent species indicate an environmental on the eastern end of the site and is associated with strati- shift from the late-Pleistocene system to the present. Two graphic deposits containing Camelops fossils, with species from the site have never before been documented surrounding sediment radiocarbon-dated to 25,600 ± 80 in the fossil record of Colorado and are important addi- 14C years BP. Locality 4086 is defined by a highly weathered tions to Colorado Pleistocene fauna. Nearby sites in the mammoth skull and surrounding fill deposits radiocarbon- San Luis Valley include the Zapata Mammoth Site, the dated to 33,405 ± 340 14C years BP. All fossils were recovered Alamosa National Wildlife Refuge Sites, Hansen Bluff, from these localities with the exception of the mammoth the Magna Site, and the Medano Mammoth Site. skull, which was too weathered to be collected.

DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 3 Alger-Meyer, Beeton, Stucky, Holen

Repositories and Abbreviations DMNS—Denver Museum of Nature & Science (his- torically, this institution was known as the Denver Museum of Natural History, so its catalogue and locality numbers use DMNH as an acronym instead) DNMH EPV–Denver Museum of Nature & Science verte- brate paleontology collections NZA—Rafter Radiocarbon Lab UGAMS—University of Georgia Center for Applied Isotope Studies MNI—minimum number of individuals VGPS—Villa Grove Paleontological Site Dental Morphology Abbreviations—(UPPER, lower): I[i], Figure 2. Boundary between the well-developed incisor; C[c], canine; P[p], premolar; M[m], molar. soil in the alluvial fan and moderately developed (younger) soil in the channel fill near locality 4086. Geology The VGPS is located in the Southern Rocky Mountains on the eastern edge of the San Juan Volcanic Field. The San Juan Mountains formed from Tertiary volcanism between 33 and 23 million years BP (Lipman 2007), and source an alluvial fan complex that dips eastward and covers the VGPS. Just up-valley of the VGPS alluvial fan is the Bonanza Caldera, the source of the 33-million years BP Bonanza Tuff. Exposed bedrock consists of a complex layering of ash flows; ignimbrite sheets; and rhyolitic, andesitic, and basaltic lavas (Lipman & McIntosh 2011). Rock fragments in the VGPS alluvial fan consist primarily of volcanic conglomerates, basalt, chert, sandstone, feldspars, quartzite, and schist. Figure 3. Coarse-grained gully fill inset into fine- Alluvial fan sediments consist of coarse alluvial grained channel fill at locality 4086. A weakly cobbles, gravels, and sands, with lenses of finer grained developed soil sits on top of the gully fill. materials. A paleolandscape buried ~12 m beneath the surface of the fan is represented by a well-developed Soil development in the fan sediment represents a buried soil with an A-Bk profile. The buried soil is con- hiatus in fan aggradation and stability on the landscape. tinuous across at least three different parent materials, The degree of soil development is strongest in the fan sedi- including (1) alluvial fan sediments; (2) a 20-m-wide ments, intermediate in the channel fill, and weakest in the channel fill composed of fine-grained, organic-rich gully fill and overlying sediments. Soils and stratigraphic sediments interpreted to be aggradational cumulic soil data are shown in Fig. 4. Stronger soil development (mod- developed in a low-energy stream setting; and (3) a erate, medium subangular blocky) in the fan sediments 1-m-wide gully fill composed of gravels and sands repre- suggests that the surface of the paleofan was stable first, senting a higher energy system that is inset into channel while the channel fill was aggrading. Slow aggradation of fill (Figs. 2 and 3). The coarser grained fan sediments are sediments and subsequent cumulic soil development con- found on both sides of the finer grained channel fill, and tinued in the channel until an erosional event initiated the channel fill is found on both sides of the gully fill. downcutting into the channel fill. Subsequent degradation

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Figure 4. Soil stratigraphic column of major sedimentary units at the Villa Grove Paleontological Site. The order of geologic events is (1) the alluvial fan aggrades; (2) the fan stabilizes and a soil develops; (3) a channel cuts, fills, and develops a cumulic soil; (4) a gully erodes into the channel fill; (5) the gully fills with coarse sediments and bones are deposited; (6) weaker soil develops on top of the gully fill, with continued soil development in the channel fill and alluvial fan; and (7) the alluvial fan continues to aggrade. Locality 4086 is best characterized by the gully and channel fill profiles, whereas locality 4085 is younger and located near the upper portion of the fan fill profile. carved a tightly meandering, 1-m-wide gully into the of a thin layer of fine sands and are encased in the silts channel fill. Sometime after the gully was cut into the of the channel fill. landscape, a high-energy fluvial event or series of events The same flood events that deposited bones in the occurred and filled the gully with gravelly sediments. base of the gully may have produced splays and overbank The majority of large mammal bones occur in flood deposits that carried some of the bones outside the one of two geological settings. First, bones occur at the meandering gully and dropped them just downstream base of the gully fill. They may have been deposited of the paleocutbanks. Encasement of these bones in the during the same high-energy flood events that deposited silts of the channel fill requires that the system returned the gravelly fill. Because the bones come out of the base to a quasi-stable, cumulic environment after the bones of the fill, they were likely deposited during earlier flood were deposited. This subsequent cumulic environment events. Second, bones occur in a higher stratigraphic deposited another ~150 mm of silty channel fill on top of position near the channel fill surface, directly next to the gully fill. Based on radiocarbon age determination of the gully fill and just downstream of the outsides of soil organic matter in the channel fill soil, the channel meander bends. These bones are typically resting on top surface was stable before 25,600 ± 80 14C years BP.

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Systematic Paleontology March 2011 by a construction crew. A paleontologi- The San Luis Valley environment is a semiarid high- cal team from DMNS excavated Pleistocene mammal altitude desert comprising grassland, sand dunes, remains from the pit in Summer 2011 and 2012. sparse shrubland, and scattered regions of dense Two bounding horizons of the site’s strata have been vegetation grading upward to the tree line. The lower radiocarbon-dated to 33,405 ± 340 (NZA-51383) and altitude basin is populated by arid plains grasses and 25,600 ± 80 14C years BP (UGAMS-08694). Fossils shrubs (Dixon 1971). The grassland vegetation grades were found in both of these strata and throughout the to sagebrush shrubland and pinyon–juniper forests interlaying sequence. These remains were identifi ed at higher elevations, with sagebrush (Artemisia spp.), at the museum and were found to consist of extant, juniper (Juniperus spp.), and pinyon pine (Pinus extinct, and extirpated species, providing an insight spp.) occurring from 2,400 to 3,000 m above sea level into the paleoenvironment of the region during the (Grauch & Keller 2004). Late Pleistocene. Villa Grove is a small town in Saguache Table 1 shows the fossil faunas recovered from the County within the northern portion of the Valley VGPS. Only mammalian material is fi gured. Gastropod (38°11’52.4” N, 105°56’22.4” W), the Alamosa Basin, shells and (probably modern) remnants of arthropods bordered by the San Juan and Sangre de Cristo moun- were also recovered from the sediments but are not tain ranges (Fig. 1). The paleontological site is a discussed. gravel pit a few kilometers south of the town, located The youngest fossils from the site stratigraphi- at an elevation of 2,434 m, and was discovered in cally are the Camelops elements, and were also the

Table 1. Faunal list and minimum number of individuals for the Villa Grove Paleontological Site, fossil taxa. *Extinct taxon. †Taxon not currently present at site.—The Bison specimens from the site likely represent B. antiquus, but they are given here as an extant taxon because accurate species identifi cation is unknown and the genus Bison has a recent historical record in the San Luis Valley. All specimens reviewed are mammalian.

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first specimens discovered. The Camelops remains in Order Proboscidea Illiger 1811 locality 4085 were fossils of the genera Brachylagus, Urocitellus, Cynomys, and Lemmiscus. The first three Mammuthus columbi Falconer 1857 of these are burrowing taxa, and at least a few individu- als were discovered in remnants of burrows, so some of Referred Specimens: DMNH EPV.63741 [right lower the fossils may be of a considerably younger age than molar m2], DMNH EPV.63739 (thoracic vertebra), 25,600 years. However, the presence of Brachylagus DMNH EPV.63740 (upper molar), DMNH EPV.63742 (left and Urocitellus, neither of which have current ranges zygoma), DMNH EPV.63749 (thoracic vertebra). within 100 km of the site, suggests that these particular burrowing specimens are not modern representatives. Proboscidean material is relatively common in North A few rodent bones found isolated in back piles of dirt American Pleistocene deposits, and may be identified may represent modern specimens and were omitted by molar and premolar morphology if other elements from the study. are fragmentary (Saunders 1970, Kurtén & Anderson The second locality, locality 4086, was found 1980, Froehlich & Kalb 1995). Mammuthus molars are initially to contain a single skeleton of Mammu- characterized by, among other features, fine lamellar thus. Dentine from a molar associated with this plates of enamel surrounding mesiodistally compressed find was dated to 33,405 ± 340 14C years BP (Holen dentine lakes that wear to a nearly flat surface, similar & Holen 2014) and was accompanied by specimens to modern Elephas (Osborn 1922, Kurtén & Anderson of Cynomys, Urocitellus, Brachylagus, Sylvilagus, 1980, Froehlich & Kalb 1995). The taxonomy of North Lepus, Equus, Bison, and Canis in strata near the American Mammuthus has been debated for well over a same horizon. As with the 4085 locality, the lower century, with some recent genomic evidence suggesting stratigraphic bounding age of the burrowing genetic similarity across populations of the two most mammals may be imprecise when coupled with sub- readily recognized North American species: M. primige- terranean activity. Bioturbation in the form of small nius and M. columbi (Enk et al. 2011). M. imperator, mammal burrows, one occupied by several immature M. jeffersonii, M. floridanus, and M. exilis have also Cynomys partial skeletons, is present in the strata. The been posited as their own species, although most are rec- Mammuthus remains were disarticulated and rede- ognized to be similar to the widespread North American posited downstream of the death site prior to burial. taxon M. columbi (Osborn 1922, Kurtén & Anderson Lighter and rounded bones were redeposited farther 1980, Agenbroad et al. 1999) or, in the case of M. jeffer- down the gully, and bones were concentrated around sonii, a possible hybridization between M. primigenius the skull in a plunge pool. Weathering is present to and M. columbi (Hoyle et al. 2004, Fisher 2009). For a high degree on many of the Mammuthus fossils our purposes, we consider M. primigenius, M. columbi, (Behrensmeyer weathering stages 3–4) and, to a lesser and M. exilis valid fossil species, with the note that M. degree, on some of the Camelops elements (Behrens- exilis is an insular taxon likely descended from M. meyer weathering stage 2) (Behrensmeyer 1978). columbi and restricted in range to the Channel Islands Some fossils from the site found in the lower strata of California (Agenbroad et al. 1999). M. columbi can showed more mineralization and darker coloration than be distinguished from M. primigenius by its larger size, the Mammuthus remains, suggesting older fossils are lower lamellar plate count in given molars, greater preserved below the Mammuthus horizon. These fossils lamellar width and spacing, and thicker enamel deposits are scant and fragmentary, and likely derive from an older (Osborn 1922, Saunders 1970, Kurtén & Anderson 1980, alluvial fan of Bull Lake age (Marine Isotope Stage 5?) Froehlich & Kalb 1995). (Rosholt et al. 1985) into which the primary alluvial fan The VGPS Mammuthus remains consist of various of the site is eroding. skeletal elements surrounding a heavily worn skull, all

DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 7 Alger-Meyer, Beeton, Stucky, Holen

presumed to belong to a single individual. Identifiable skeletal elements indicates that the fossils remained on material includes a partial left m2, the root base of an the surface for several years prior to burial by fluvial upper molar, a left zygoma, a complete thoracic vertebra, sediments. Some of the vertebrae and molars were shel- a thoracic vertebra centrum, and numerous fragments tered partially or fully by other skeletal elements and are of bone and dental material. The late-stage weathering better preserved. The distribution of some fossil elements of the skull renders it poor for identification purposes, on a shallow incline indicates that sediments may have although some isolated teeth preserve the occlusal moved the bones slightly from their original position. morphology of the lamellae. An accurate Laws’s age The M2 bears relatively wide spacing between the class assignment (Laws 1966) cannot be determined as lamellae and a close morphological resemblance to a result of the fragmentary nature of the material and M. columbi. Nine lamellar plates are fully preserved, the lack of lower teeth. However, because the right second including the three posteriormost, which are broken upper molar (M2) (DMNH EPV.63741, Fig. 5) is abraded into ovate to subrounded lophs; all are abraded to through to the posterior end of the occlusal surface but some degree. The lamellar frequency is approximately the plates are not heavily attrited, the M2 may be placed eight lamellae per 100 mm, and the average width of in Louguet’s attrition level of C to D1, which estimates the enamel is 2.15 mm. Although the enamel is slightly the age of the individual to be on the upper end of 22 narrower in the VGPS specimen than the average for to 35 years of age (Louguet 2002). The weathering M. columbi, this is within the variation for the species (Behrensmeyer stage 4) of the VGPS skull and most other (Kurtén & Anderson 1980), and the molar structure more closely matches that of M. columbi than M. primigenius. Based on these features, the species present at the VGPS is designated as Mammuthus columbi. This taxon is known from a handful of sites in Colorado, including the Ziegler Reservoir Fossil Site (Sertich et al. 2014).

Order Lagomorpha Brandt 1855

Brachylagus idahoensis Miriam 1891

Referred Specimens: DMNH EPV.62800 (cranium), DMNH EPV.62801 (partial cranium and partial skel- eton), DMNH EPV.63784 (left M3), DMNH EPV.63785 (right M3), DMNH EPV.63786 (left M2), DMNH EPV.63787 (right M2), DMNH EPV.63788 (left M1), DMNH EPV.63789 [left upper premolar (P) 4], DMNH EPV.63790 (right P3), DMNH EPV.63791 (left P3), DMNH EPV.63784 (right P2), DMNH EPV.63793 (left dentary), DMNH EPV.63950 (right dentary).

There are four leporid genera currently found in North Figure 5. Villa Grove Paleontological Site America: Sylvilagus (cottontail rabbits), Brachylagus Mammuthus columbi left lower molar 2 (DMNH (pygmy rabbits), Lepus (hares), and Romerolagus EPV.63741), occlusal view. Scale = 100 mm. (volcano rabbits) (Green & Flinders 1980, Cervantes et

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Figure 6. Average lower premolar (p) 3 length and width measurements in major North American lagomorphs. Adapted from Ramos (1999a, b), and Jass (2009). DMNH63793, DMNH 63950 (Brachylagus), and DMNH63799 (Sylvilagus) are included for comparison. Specimens assigned letters are as follows: A, North American fossil Ochotona; B, Brachylagus idahoensis; C, B. coloradoensis; D, Sylvilagus bachmani; E, S. nuttallii; F, S. audubonii; G, S. floridanus; H, L. americanus; I, L. townsendii; J, L. californicus; K, L. arcticus; and L, L. alleni. The Villa Grove Paleontological Site fossil specimens are given by their DMNH catalogue number. Some lagomorph species with restricted ranges or those that are found in more southern locations (i.e., southern Mexico, eastern United States) are not included. Error bars represent standard deviation. All units are in millimeters. al. 1990, Oliver 2004). The small lagomorph Ochotona EPV.63950, and DMNH EPV.63800. Ochotonids, which (pikas) is also found throughout North America, includ- include the North American species O. princeps and O. ing Colorado (Smith & Weston 1990). Brachylagus collaris, may be distinguished from lagomorphs based idahoensis has been classified occasionally within the on several dental character, including smooth ridges genus Sylvilagus (e.g., Orr 1940, Grayson 1988, Grayson on upper molar reentrant angles, an anterior reentrant 1985) and was designated originally as a species of Lepus on the P3, and a triangular p3 with two external reen- (Merriam 1891), but most recent sources agree it is dis- trant angles and one to two interior reentrant angles tinct genetically and morphologically from Sylvilagus (Smith & Weston 1990, Jass 2009, Fostowicz-Frelik et al. (e.g., Oliver 2004, Estes-Zumpf et al. 2014), and we there- 2010). The P2 of Brachylagus has a rounded occlusal fore consider Brachylagus a distinct genus after Lyon surface that contains a single anterior reentrant angle (1904). North American Pleistocene fossil lagomorphs (Hibbard 1963). The single anterior reentrant angle is can be distinguished by size, cranial morphology, limb seen in modern Nesolagus, a Southeast Asian leporid, proportions, and dental morphology, especially the struc- and in the Pliocene lagomorph Hypolagus (Hibbard ture of the P2 and lower premolar (p) 3 occlusal surface 1963, 1969). The Nesolagus P2 differs in form from (Hibbard 1963, Grayson 1977, Russell & Harris 1986, Dal- that of Brachylagus by being generally shallower, more quest et al. 1989, White 1991, Ramos 1999b, Jass 2009). elongate, and larger (Hibbard 1963, Averianov et al. Figure 6 shows the relative length and width ratios 2000). P2 character in Hypolagus are similar to those among some North American lagomorph taxa p3s com- in Brachylagus, but the tooth is larger in Hypolagus pared with VGPS specimens DMNH EPV.63793, DMNH (Hibbard 1969, Ramos 1999a).

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Figure 7. Villa Grove Paleontological Site (VGPS) Brachylagus elements from the VGPS. (A) Cranium (DMNH EPV.62800), ventral view. (B) Left dentary (DMNH EPV.63793), dorsal view. (C) Right dentary (DMNH EPV.63950), dorsal view. (D) Right upper second premolar (P2) (DMNH EPV.62800), occlusal view. (E) Left P2 (DMNH EPV.62800), occlusal view. (F) Left lower third premolar (p3) (DMNH EPV.63793), occlusal view. (G) Right p3 (DMNH EPV.63950), occlusal view. (H) Right scapula (DMNH EPV.62801), lateral view. (I) Left innominates (DMNH EPV.62801), lateral view. (J) Right innominates (DMNH EPV.62801), lateral view. (K) Atlas (DMNH EPV.62801), anterior view. (L) Posterior thoracic vertebra (DMNH EPV.62801), dorsal view. (M) Posterior thoracic vertebra (DMNH EPV.62801), dorsal view. (N) Sacrum (DMNH EPV.62801), dorsal view. (O) Left humerus (DMNH EPV.62801), anterior view. (P) Left radius (DMNH EPV.62801), anterior view. (Q) Left femur (DMNH EPV.62801), anterior view. (R) Left tibia (DMNH EPV.62801), anterior view. (S) Right humerus (DMNH EPV.62801), anterior view. (T) Right radius (DMNH EPV.62801), anterior view. (U) Right femur (DMNH EPV.62801), anterior view. (V) Right tibia (DMNH EPV.62801), anterior view. Scale: A–C, 10 mm; D–G, 1 mm; H–N, 30 mm; O–V, 30 mm.

10 DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 Villa Grove Paleontological Site Fossils and Paleoenvironment

In Brachylagus, the p3 trigonid and talonid basins stratigraphic age deposits and are not older than about are separated by an elongate posterior external reentrant 33,000 years. Small lagomorphs were found at both VGPS angle (Dalquest et al. 1989, White 1991) that usually localities 4085 and 4086. runs the entire width of the tooth, although occasionally The VGPS small lagomorph material bears the the channel is incomplete at the farthest lingual edge morphology of leporids rather than ochotonids, and (Hibbard 1963). This is a unique character that can overall size measurements and leg proportions best distinguish B. idahoensis from other leporids, particu- match those of the genus Brachylagus (Fig. 7). The larly the extinct taxa B. coloradoensis and Hypolagus upper premolars of DMNH EPV.62800 and DMNH (Hibbard 1963, 1969, Ramos 1999a). B. coloradoensis EPV.63792 both bear the single prominent reentrant and Hypolagus have a larger p3 length and width than angle characteristic of Brachylagus (Fig. 7D, E). The Brachylagus idahoensis, with Hypolagus being the third premolars of the dentaries DMNH EPV.63793 and largest of the three (Gazin 1934, Ramos 1999a). Hypo- DMNH EPV.63950 (Fig. 7F, G) show distinct trigonid lagus is distinguished most easily from Brachylagus by and talonid enamel lakes separated by a posterior an external reentrant fold that runs partway through reentrant channel running buccolingually through the tooth and bears a simpler enamel pattern than in the midsection of the premolar, as in B. idahoensis. Brachylagus (Gazin 1934, Ramos 1999a). In B. colora- The posterior reentrant angle of DMNH EPV.63793 doensis, the p3 posterior reentrant fold extends roughly (Fig. 7F) does not extend fully through the tooth, with half to two thirds of the way through the center of the a thin corridor connecting the two enamel lakes. The premolar, and the overall tooth is slightly larger than in channel is narrow and restricted farther anteriorly than B. idahoensis (Ramos 1999a). B. idahoensis teeth are reports of B. coloradoensis, and comparisons with B. smaller than all other mature extant leporids (Gazin coloradoensis material from the Porcupine Cave Site 1934, Hibbard 1963, Ramos 1999a, b; also see Fig. 6). matrix found a distinct difference in the depth of the Lagomorph specimens from the VGPS represent- reentrant angle projection as well as the overall molar ing small leporids include several postcranial elements, size (personal observation). The pattern seen on DMNH a partial disarticulated skeleton, two dentaries, isolated EPV.63793 is well within the regular variation of the teeth, and a cranium with a complete molar row. All lago- species (Hibbard 1963, Ramos 1999b). Size compari- morph material from the site is from adult specimens, sons of the VGPS third premolars to other lagomorphs as evidenced by fused epiphyses, fully erupted molar showed a strong similarity to the average values of sequences, and tooth wear. Specimens DMNH EPV.63784, Brachylagus idahoensis, and although slightly smaller DMNH EPV.63785, DMNH EPV.63786, DMNH EPV.63787, than average for modern B. idahoensis, the specimens DMNH EPV.63788, DMNH EPV.63789, DMNH EPV.63790, were within the standard deviation of the premolar DMNH EPV.63791, and DMNH EPV.63793 were excavated measurements (Fig. 6). from the same location and associated with DMNH Differences between the VGPS Brachylagus and EPV.62801, constituting at least one partial skeleton, comparative modern B. idahoensis were not numerous including an intact dentary and the majority of the upper or prominent, although we note that the palate of DMNH molar row. The cranium DMNH EPV.62800 contains a EPV.62800 (Fig. 7A) is somewhat wider and more con- full molar row and partial rostrum with intact incisors. stricted anteroposteriorly than is typical of B. idahoensis. The dentaries DMNH EPV.63793 and DMNH EPV.63950 Based on the morphological features, we conclude that show differential wear and slight size disparity, suggest- the Brachylagus specimens at the VGPS belong to the ing they belong to different individuals. The actual age of taxon Brachylagus idahoensis. This species is currently the small lagomorph specimens is difficult to determine restricted to a region in the Great Basin and surrounding because of burrowing activity, but based on the superposi- areas within Idaho, Oregon, Nevada, Utah, Montana, Cali- tion of the burrow fill, they are bounded by the lowermost fornia, and Wyoming (Green & Flinders 1980, Campbell

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et al. 1982, Larrucea 2007). The presence of small popu- angle, and both an anterior and posterior external lations of modern Brachylagus was confirmed in 2014 by reentrant angle are visible on the anterior (abraded) and fecal pellet genetic analysis in the northwestern corner of posterior occlusal surfaces. The anterior external reen- Colorado near the Wyoming border (Estes-Zumpf et al. trant angle is faint and narrow, but appears to extend 2014), but B. coloradoensis specimens from Porcupine relatively far into the trigonid basin, terminating below Cave are the only known fossils of the genus in Colorado the anterior reentrant angle. The posterior external reen- (Ramos 1999a). The Brachylagus idahoensis specimens trant angle is partially obscured by the break between the from the VGPS currently represent the only known fossil trigonid and talonid, but the morphology of the enamel occurrence of this species in Colorado. border is still preserved. There is some evidence of small crenulations on the posterior enamel border of the cf. Sylvilagus nuttallii Bachman 1837 posterior external reentrant angle, whereas the anterior border appears generally smooth where visible. Referred Specimens: DMNH EPV.63800 (right dentary), The length and width measurements for the tooth DMNH EPV.63801 (left P4) most closely match the average values given by Ramos (1999b) for Lepus americanus (Fig. 6), but are also Cottontail rabbits, members of the genus Sylvilagus, are within the range of variation for the p3 in various species represented in North America by fifteen extant species, of Sylvilagus. The p3 occlusal surface is obscured, of which S. nuttallii, S. audubonii, and S. floridanus but the visible crenulations and reentrant angle are are present in Colorado (Hay 1921, Chapman 1975, comparable to specimens of Lepus americanus and Chapman & Willner 1978, Chapman & Ceballos 1990). Sylvilagus nuttallii. Moderate wear on the p3 suggests it As with other leporids, identification of species in the belongs to an adult individual. The dentary height and fossil record is made based primarily on size, cranial morphology, and the p3 occlusal pattern, although the P2 pattern may also be useful (Hibbard 1963). The anterior wall of the posterior external reentrant of the p3 is strongly crenulated in S. audubonii and smoother in S. nuttallii and S. floridanus, usually lacking crenulations on the anterior wall of the reentrant angle (Dalquest et al. 1989). This pattern continues through to the base of the tooth, with some sharper definition according to Dalquest et al. (1989). Sylvilagus occurs at locality 4086 of the VGPS and is represented by the posterior portion of a right dentary (DMNH EPV.63800) containing a p3 and a lower first incisor (i1), and an isolated left P4 (DMNH EPV.63801). Both specimens are in poor condition, but the p3 occlu- sal morphology is partially preserved on the dentary and offers a potential species identification. In Fig. 8, we adjusted the focus so that both the trigonid and talonid Figure 8. Villa Grove Paleontological Site cf. basins are aligned and in focus, although there is a thin Sylvilagus nuttallii right third lower premolar gap between the basins where the anterior enamel border (DMNH EPV.63799), occlusal view. Note anterior of the posterior external reentrant angle connects to the portion occlusal abrasion. Scale = 3 mm. reentrant channel. There is a single anterior reentrant

12 DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 Villa Grove Paleontological Site Fossils and Paleoenvironment depth are less than comparative L. americanus, and the cranial material, especially fragmentary as in this case, length of the diastema is short compared to specimens is not typically diagnostic to species level, so we refer to of S. audubonii and L. americanus. The tooth size this specimen as Lepus sp. is relatively large overall, but comparable to modern S. nuttallii from Colorado (personal observation). Order Rodentia Bowdich 1821 We believe the dentary dimensions and p3 occlusal morphology most closely resemble those of S. nuttal- Lemmiscus curtatus Thomas 1912 lii. Given the fragmentary condition of the p3 and the similarities to L. americanus, however, we designate Referred Specimen: DMNH EPV.63850 (left dentary). the tooth as belonging to cf. Sylvilagus nuttallii, in that it bears a stronger resemblance to S. nuttallii than to A single left dentary (DMNH EPV.63850) of an arvicoline other leporids. The left P4 is not diagnostic beyond the rodent is present from locality 4085 of the VGPS and genus Sylvilagus, and is left as Sylvilagus sp. contains an intact m1 and m2 (Fig. 10B). The dentary matches the size of modern Lemmiscus, and further Lepus sp. morphological similarity is observed in both molars (Bell & Mead 1998, Barnosky & Bell 2003). The m1 Referred Specimen: DMNH EPV.63774 (right humerus). contains seven distinct triangles and an anterior loop within the morphological variation of L. curtatus (Fig. Lepus is a genus of large leporids common worldwide, 10A). The buccal wing of the triangles is more developed including in Colorado. The only material referable than the lingual wing in DMNH EPV.63850, which is also to large leporids recovered from the VGPS is the distal consistent with Lemmiscus morphology (Bell & Mead portion of a right humerus from locality 4085. It is 1998, Barnosky & Bell 2003). These traits distinguish the characteristically constricted with deep articulatory specimen as Lemmiscus and show no clear divergence grooves (Fig. 9), and measures 10.86 mm in width, from the only currently known species, L. curtatus, so we larger than Sylvilagus and appropriate for Lepus. Post- assign these specimens as Lemmiscus curtatus.

Figure 10. Villa Grove Paleontological Site Lemmiscus curtatus right dentary (DMNH Figure 9. Villa Grove Paleontological Site EPV.63850). (A) Lower first molar, detail, Lepus sp. right distal humerus (DMNH occlusal view. (B) Dentary fragment, dorsal EPV.63744), anterior view. Scale = 10 mm. view. Scale: A, 1 mm; B, 10 mm.

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Urocitellus (= Spermophilus) sp. the p4 relative to the trigonid, but extended in m1–m2 (Fig. 11A). The m1 and m2 are slightly narrower Referred Specimens: DMNH EPV.63772 (left dentary), mesiodistally than buccolingually, but rounded mesi- DMNH EPV.63773 (left dentary), DMNH EPV.63771 ally with subrounded basins between the metaconid (partial skeleton). and protoconid. In some teeth, these basins pinch out where the protoconid starts to form. The p4 is nearly The ground squirrels (Marmotini) of the North the same size as the m1, but both are smaller than the American Pleistocene and Holocene include the genera m2. The trigonids of p4–m2 are all raised considerably Paenemarmota, Marmota, Cynomys, Spermophilus, higher than the talonid. The m3 is larger than the Ictidomys, Notocitellus, Callospermophilus, Otosper- other molars and resembles, superficially, a Cynomys mophilus, Poliocitellus, Xerospermophilus, Urocitellus, m3, but differs mainly in having a shallower relative and Ammospermophilus, all of which except Paene- topography, smaller size, and reduced depth in the marmota are extant (Herron et al. 2003, Helgen buccolingual channel between the metalophid and the et al. 2009, White & Morgan 2005). The modern talonid basin. The trigonid basin is slightly raised and diversity of the Marmotini is well-established, but abraded in a pattern comparable to that of the other several taxa have an understudied fossil record, molar trigonids. The m3 hypoconid is deflected slightly particularly those formerly in the genus Sper- anteriorly, as in some Cynomys. mophilus (Spermophilus, Ictidomys, Notocitellus, The teeth are relatively large, and the p4 is larger Callospermophilus, Otospermophilus, Poliocitellus, than in many comparative specimens of medium-size Xerospermophilus, Urocitellus) (Helgen et al. 2009). Marmotini, although smaller relative to the molar row Paenemarmota, Marmota, Cynomys, and Ammo- than in Cynomys, Marmota, and Paenemarmota. Some spermophilus may be readily distinguished by size of the dental characters are comparable to Cynomys, when mature; all other taxa generally fall within the but differ considerably in size and in the morphology dimensions between those of larger Cynomys and of the p4–m2. The distance between the protoconid and Ammospermophilus (Goodwin 2004, Helgen et al. hypoconid on the m1–m2 is considerably shorter relative 2009). Cranial characteristics, maxillary dental mor- to the buccolingual width than in Cynomys, and all the phology, and occasionally dentary morphology may be used to differentiate different members of the Marmo- tini (Goodwin 2004, Helgen et al. 2009). Small Marmotini material from the VGPS that is morphologically distinct from Cynomys includes four dentaries, two of them isolated (DMNH EPV.63772, DMNH EPV.63773), and the other belonging to a partial skeleton (DMNH EPV.63771). DMNH EPV.63771 contains a full molar row (Fig. 11), whereas DMNH EPV.63772 contains a p4–m1, and DMNH EPV.63773 contains an isolated m2. The p4 on both DMNH EPV.63771 and DMNH EPV.63772 is relatively large Figure 11. Villa Grove Paleontological and rounded in outline, with a metaconid, entoconid, Site Urocitellus sp. right dentary (DMNH hypoconid, and protoconid of roughly equal size as EPV.63771). (A) Detail of p4, occlusal view. well as a smaller protolophid that forms the anterior (B) Detail of m3, occlusal view. (C) Dentary, rim of a small basin between the metaconid and pro- dorsal view. Scale: A–B, 3 mm; C, 10 mm. toconid (Fig. 11A). The talonid is slightly reduced in

14 DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 Villa Grove Paleontological Site Fossils and Paleoenvironment molars are rounder in outline. DMNH EPV.63772 belongs DMNH EPV.63813 (right dentary), DMNH EPV.63814 to an adult individual with worn dentition, whereas (left dentary), DMNH EPV.63827 (right M3), DMNH DMNH EPV.63771 shows adult dentition and skeletal EPV.63828 (left M2), DMNH EPV.63829 (right M2), development, but with a less abraded occlusal surface. We DMNH EPV.63830 (left M3), DMNH EPV.63831 (left M1), take these specimens to represent adult animals, as well DMNH EPV.63832 (right M1), DMNH EPV.63833 (left as the associated skeletal material and dentary of DMNH M3), DMNH EPV.63834 (left dentary), DMNH EPV.63835 EPV.63773, which contain a heavily abraded m2 and are (right P4), DMNH EPV.63836 (left P3), DMNH EPV.63837 not currently diagnostic beyond Marmotini. Postcranial (right dentary), DMNH EPV.63838 (right P3), DMNH and maxillary elements are also not sufficient to distin- EPV.63839 (left maxilla), DMNH EPV.63840 [left first guish the taxa beyond Marmotini. The upper dentition upper incisor (I1)], DMNH EPV.63841 (right I1), DMNH in isolated specimens is too fragmentary to be identified EPV.63842 (left I1), DMNH EPV.63843 (right I1). clearly, but can be readily distinguished from Cynomys. The general morphology and size of the dentaries most Members of the genus Cynomys (prairie dogs) are large, closely resembles comparisons to members of the genus plains-dwelling ground squirrels (clade Marmotini) Urocitellus based on comparisons to specimens in the endemic to western and central North America. The DMNS zoological collections, and are also very similar genus is represented by five extant species (C. ludovi- to Porcupine Cave specimens described by Goodwin cianus, C. leucurus, C. gunnisoni, C. parvidens, and (2004) as Spermophilus cf. elegans. DMNH EPV.63771 C. mexicanus) and seven extinct species (C. vetus, C. and DMNH EPV.63772 are similar in morphology to the hibbardi, C. sappaensis, C. spenceri, ?C. andersoni, species U. richardsonii, U. elegans, and U. beldingi. C. niobrarius, and C. churcherii), all found in North There is some resemblance in the occlusal surface of America (Hollister 1916; Clark et al. 1971; Pizzimenti & the lower molar row—in particular, the relative size of Hoffmann 1973; Eshelman 1975; Burns & McGillivray the p4—to the “townsendii” group of Urocitellus (par- 1989; Goodwin 1993, 1995a, b; Hoogland 1996; Goodwin ticularly U. townsendii, U. mollis, and U. canus), but 2004). The extinct taxa are known from Pliocene to comparisons to modern specimens found these characters late-Pleistocene deposits in Kansas, Nebraska, Colorado, to vary considerably, which in combination with the and Alberta, and are generally distinguished by cranial larger size of the VGPS specimens and the morphological characteristics and maxillary dentition, as well as lower differences in other dentary features make the similarity dentition in C. hibbardi, C. spenceri, C. sappensis, and to the “townsendii” group likely an artifact. The species ?C. andersoni (Goodwin 1995b, Goodwin 2005). designation is currently unclear for the VGPS specimens, Cynomys is somewhat similar morphologically to and they are therefore designated as Urocitellus sp. other moderately large Marmotini, but larger cheek teeth, Specimens are present at both localities of the VGPS. U. more heavily built jaws, a distinct lophid and cuspulids elegans is the only species of Urocitellus extant in Colo- on the talonid of the upper first and second molars, a rado, and occurs on the northern edge of the state, but is well-developed basin along the ectolophid of the M3, and not currently present in the San Luis Valley. large auditory bullae relative to other ground squirrels can be used to identify Cynomys (Goodwin 1995b, Helgen Cynomys (Leucocrossuromys) cf. gunnisoni et al. 2009). Fossils of extant Cynomys species may be dis- Baird 1855 tinguished somewhat by relative size and, more reliably, by cranial measurements and dental occlusal morphol- Referred Specimens: DMNH EPV.63802 (left dentary), ogy, particularly that of the maxillary alveolar row DMNH EPV.63806 (left dentary), DMNH EPV.63810 (left (Goodwin 1995a, b). However, Goodwin (1995b) notes dentary, right metatarsal, right rib), DMNH EPV.63811 that size and morphology of fossil and modern specimens (right dentary), DMNH EPV.63812 (left dentary), of Cynomys believed to belong to the same species can

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be variable, and species differentiation is often less reli- the specimens were found at locality 4086 and appear able than subgenus identification. The two subgenera concentrated near the 33,405 ± 340-14C years BP of Cynomys (Cynomys and Leucocrossuromys) have horizon, although their actual age is uncertain as a characteristic osteological features seen in both extant result of the tendency of this taxon to burrow. Several and extinct species (Goodwin 1993, 1995a, b). An enamel isolated teeth and bones accounting for at least three bridge runs across the center of the m3 in the subgenus individuals were found in a single burrow infill deposit, Leucocrossuromys, connecting the talonid basin to the suggesting at least some of the specimens are younger ectolophid (Goodwin 1995b). Members of the subgenus than 33,405 ± 340 14C years BP. Cynomys (C. ludovicianus and C. mexicanus) are not Reliable comparison of VGPS material to extinct known to show this feature, and bear a strong anterior Cynomys is difficult as a result of the lack of intact deflection in the m3 hypoconid (Goodwin 1995b). The cranial material. When comparisons are possible, none enamel bridge characteristic of Leucocrossuromys of the specimens show the distinguishing dental mor- may be reduced or absent in C. gunnisoni according to phologies of the extinct species of Cynomys described Goodwin (1995b), and C. gunnisoni may have a more by Goodwin (1995b). All the dentaries and lower third anteriorly deflected m3 hypoconid, which is similar mor- molars from the VGPS were analyzed for the presence phologically to members of the subgenus Cynomys. or absence of a bridge in the m3, and with the exception Cynomys is the most common fossil found at of a few specimens that were too worn to show distinct the VGPS, with a minimum number of individuals occlusal morphology, all the lower third molars bore this at six based on lower left third molars. Some of the feature (Fig. 12A, B). Because the m3 bridge is found Cynomys material is associated with partial skeletons, only in members of the subgenus Leucocrossuromys, we although most is isolated. Juveniles, adults, and mature designate this as the subgenus of the VGPS specimens. individuals are represented in the samples based on The m3 hypoconids of some specimens (Fig. 12B) show a occlusal wear, epiphyseal fusion, and bone porosity. All slight anterior deflection characteristic of C. gunnisoni,

Figure 12. Villa Grove Paleontological Site Cynomys cf. gunnisoni dentary elements. (A) Left lower third molar (m3) detail (DMNH EPV.63813), occlusal view (reversed image). (B) Left m3 detail (DMNH EPV.63802), occlusal view. (C) Right alveolar row (DMNH EPV.63813), occlusal view. (D) Left dentary (DMNH EPV.63802), dorsal view. (E) Right dentary (DMNH EPV.63802), lateral view. (F) Left dentary (DMNH EPV.63802), lateral view. Scale: A–B, 3 mm; C–F, 10 mm.

16 DENVER MUSEUM OF NATURE & SCIENCE ANNALS | No. 8, December 23, 2019 Villa Grove Paleontological Site Fossils and Paleoenvironment although this feature is variable among VGPS specimens. Assignment of Late Pleistocene species of equids has DMNH EPV.63802 (Fig. 12B) demonstrates the anterior been problematic for decades for multiple reasons, hypoconid deflection and transverse enamel bridge often related to poor type specimen designations and characters in tandem. Goodwin (1995b) performed a disagreement over which species should be considered morphometric analysis of Leucocrossuromys species valid (Scott 2004, Heintzman et al. 2017). More than traits and found variation between C. leucurus, C. gun- thirteen species of Pleistocene North American equids nisoni, and C. parvidens based on dentary material that have been proposed, many of which are considered was generally nondiagnostic, but Goodwin (2004) used a invalid by one or more authors (Gidley 1901, Dalquest discriminant function model on a sample of Porcupine & Hughes 1965, Lundelius & Stevens 1970, Dalquest Cave Cynomys to determine a probable identification 1979, Harris & Porter 1980, MacFadden 1992, Scott for the sample out of C. gunnisoni and C. leucurus. 2004). In general, North American Pleistocene equids Our own comparisons between the VGPS specimens and may be organized by size (large, medium, or small), recent Colorado C. leucurus and C. gunnisoni found and whether they were “stout-legged,” with relatively a slightly closer affinity to C. gunnisoni in their molar short limb proportions, or “stilt-legged,” with longer proportions, although given variation in the ages and the limb proportions (Dalquest 1979, MacFadden 1992, relatively small sample size of VGPS specimens, we do not Scott 2004, Heintzman et al. 2017). All late-Pleistocene find this affinity significantly meaningful. equids were formerly placed in the genus Equus, The average measurements of dentary elements although a recent paleogenetic study by Heintzman et from the VGPS closely match those of modern C. gun- al. (2017) suggests that a New World stilt-legged group nisoni given in Goodwin (2004). Members of Cynomys of equids belongs in its own genus (Haringtonhip- are not typically sympatric, although their ranges may pus) with one known species: H. francisci. The state of overlap somewhat near their borders (Pizzimenti & stout-legged equids remains complicated. Scott (2004), Hoffmann 1973), so we think the VGPS specimens likely however, provides a baseline we use for our identifica- represent a single species altogether, given their close tion of the VGPS equid material. Scott (2004) considers stratigraphic proximity. We are confident this material E. simplicidens, E. cumminsi, E. conversidens, E. represents a member of the subgenus Leucocrossuromys. scotti, and E. “occidentalis” valid species and also The m3 morphology of some of the dentaries suggests recognize a broad group of North American equids the material represents C. gunnisoni, although we traditionally referred to as hemionines. Heintzman et accept uncertainty associated with individual variation al. (2017) point out that the association of the stilt- and a lack of diagnostic cranial material. We therefore legged morphotype with hemionines is inconsistent with designate the VGPS Cynomys material as Cynomys cf. genomic data, which in their study recovers the North gunnisoni. C. gunnisoni is currently found at the site, American stilt-legged group as distinct from modern so at least some skeletal material may be intrusive. hemionine Equus. E. conversidens is particularly problematic Order Perissodactyla Owen 1848 because it has been described variably as a stilt-legged and stout-legged horse, and its holotype is nondiagnos- Equus cf. conversidens Hay 1915 tic (McFadden 1992, Scott 2004, Heintsman et al. 2017). Scott (2004) proposed to recognize E. conversidens as Referred Specimens: DMNH EPV.63758 (right meta- a valid species for its widespread historical use until a carpal 3), DMNH EPV.63763 (left M3), DMNH EPV.63759 neotype can be assigned to clarify its identification. (left m3, left m2), DMNH EPV.63763 (right M3), DMNH Because the criteria used to assign material to E. con- EPV.63757 (left femur). versidens have varied, we consider E. conversidens a tentatively valid taxon according to the features

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Figure 13. Villa Grove Paleontological Site Equus cf. conversidens representative elements. (A) Left lower second molar (m2) (EPV.63759), occlusal view. (B) Left m3 (EPV.63759), occlusal view. (C–E) Right metacarpal (DMNH EPV.63758) proximal view (C), anterior view (D), and posterior view (E). Scale: A–B, 50 mm; C–E, 100 mm. described by Dalquest (1978), Kurtén & Anderson slightly worn, indicating the animal was a young (1980), and Scott (2004). These features include pri- adult. Some of the fragmentary teeth show differential marily small, stout limb proportions. Metapodial size, wear and size, which suggest they belong to more molar ectoflexid depth, and linguaflexid morphology than one individual. The complete teeth appear to be have been proposed as a means of identifying species from a single individual. All equid material from the of North American Pleistocene equids, although the VGPS was found at locality 4086 near the mammoth shape of the linguaflexid can vary among modern and skull and at the 33,405 ± 340-14C year BP horizon. extinct equid populations (Gidley 1901, Dalquest 1979, The VGPS metacarpal (DMNH EPV.63758) is small: MacFadden 1992). Enamel wear also slightly affects the 230 mm in length, 29.7 mm mediolaterally across the extent of folding on the occlusal surface (Gidley 1901, center of the shaft, 45.0 mm at the widest portion of MacFadden 1992). the proximal base, and 40.0 mm at the greatest width Of the referred equid specimens, only the meta- of the distal head. The DMNH EPV.63759 m3 and p4 carpal and lower molars (Fig. 13) are in a condition are each flattened buccally with a fairly narrow, rect- that warrants potential species identification. The angular protoconid and hypoconid, and a relatively teeth are moderately weathered but fully erupted and elongate metaconid and metastylid with pinched

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Figure 14. Measurements of third metacarpals from representatives of North American equid species based on data from Gazin (1936), Willoughby (1948), Lundelius & Stevens (1970), and Harris & Porter (1980). Taxa are named according to Scott (2004) and Heintzman et al. (2017). Specimens assigned letters are as follows: A, Equus conversidens; B, Haringtonhippus francisci; C, E. simplicidens; D, E. “occidentalis”; E, E. scotti. Equid species are not typically identifiable through metapodials alone, but they may be assigned general size categories based on metapodial dimensions (Scott 2004, Sertich et al. 2014, Heintzman 2017). E. cumminsi is primarily identified by dental morphology (Dalquest 1975) and is therefore omitted. All measurements are in millimeters. channels near the ectoflexid. The linguaflexid valleys Order Artiodactyla Owen 1848 are broad and V shaped, opposite a small, moderately shallow ectoflexid. An isthmus is present at the base Camelops sp. of the channel connecting the metastylid of the m3. A similar feature can be seen to a lesser degree in the Referred Specimens: DMNH EPV.63755 (left fused m2, where it is interrupted by the buccal tip of the metacarpals 2 and 3), DMNH EPV.63750 (left proximal ectostylid. The m3 is 33.56 mm in length and 14.25 phalanx), DMNH EPV.63752 (left carpals), DMNH mm in width, whereas the p4 is 32.28 mm in length EPV.63754 (left pelvic fragment), DMNH EPV. 63767 and 16.44 mm in width. (partial molar), DMNH EPV.63753 (thoracic vertebra). The VGPS metacarpal most closely matches the average dimensions for Equus conversidens given by The VGPS camelid specimens are represented by a Dalquest (1979) and Dalquest & Hughes (1965) (Fig. presumed single individual found at locality 4085 in 14). The teeth resemble the general morphology of soil dated to 25,600 ± 80 years BP. Material includes a Equus conversidens, which is described by Dalquest metacarpal (Fig. 15), three carpal bones, a phalanx, a (1979) as broad and containing metaconid–metas- partial pelvis, a partial thoracic vertebra, and associ- tylid valleys that are U shaped or broadly V shaped. ated bone fragments. The metacarpal bears the general The m2 and m3 are somewhat longer than is typical morphology of Camelidae, consisting of two fused for E. conversidens. Recognizing the imprecision of metacarpals with a Y-shaped split at the distal end. The a species designation made based on a problematic size and width indicates Camelops, although it is not taxon, we denote the VGPS equine material as Equus cf. diagnostic to the species level (Kurtén & Anderson 1980, conversidens. Dalquest 1992, Zazula et al. 2016). Dalquest (1992) notes that tooth morphology can be of limited value

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Figure 15. Villa Grove Paleontological Site Camelops sp. left fused metacarpals (DMNH EPV.63755), anterior view. Scale = 100 mm.

because occlusal features can vary considerably depend- as Bison. The third molar is fully erupted and slightly ing on the state of wear. Dalquest (1992) recommends worn, indicating the animal was an adult at the time that, unless sufficient cranial and dental remains are of death. The age and location of the VGPS Bison present, most American Pleistocene camelids are best specimens are consistent with the age and range left unspecified beyond the genus level. Because no fully of the species B. antiquus, according to McDonald intact camelid teeth or cranial materials have been (1981). Comparison to B. latifrons specimens from found at the site, the Camelops specimens are left as the Ziegler Reservoir Fossil Site suggests the VGPS Camelops sp. Camelops is known from several dozen specimen belongs to a smaller species. However, there sites in Colorado, including the Ziegler Reservoir Fossil is insufficient study on the lower tooth morphology Site and Porcupine Cave (Sertich et al. 2014). of extinct Bison as a means of identifying species, and no postcranial material or horn cores have been Bison sp. recovered from the VGPS. Although the material likely belongs to Bison antiquus based on the distribu- Referred Specimens: DMNH EPV.63766 (right dentary), tion and time range of the species, the VGPS material DMNH EPV.63748 (lower molar). cannot be identified with certainty to the species level, and is therefore be left as Bison sp. Bison specimens Bison are widespread in North American and Eurasian are known from several sites in Colorado. fossil records, and numerous species including B. lati- frons, B. antiquus, B. priscus, B. occidentalis, and Order Carnivora Bowdich 1821 the modern B. bison are known from North America (Lucas 1899, McDonald 1981). Species are designated Canis dirus Leidy 1858 primarily based on horn core morphology (Lucas 1899, McDonald 1981). Referred Specimens: DMNH EPV.63747 (left m1), The VGPS Bison specimens consist of a single ?DMNH EPV.63746 (left second metatarsal). right dentary (DMNH EPV.63766) (Fig. 16) with all molars present but fragmentary, and one isolated Canis is represented in the North American Pleistocene lower molar (DMNH EPV.63748). The dentary is paleontological record by seven species: C. lupus, C. bovine with hypsodont dentition and has an accessory latrans, C. rufus, C. dirus, C. lepophagus, C. arm- column on the lower third molar which designates it brusteri, and C. edwardii (Nowak 1979). C. lepophagus,

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Figure 16. Villa Grove Paleontological Site Bison sp. left dentary (DMNH EPV.63766), lateral view. Scale = 100 mm. C. armbrusteri, and C. edwardii lived during the early Among the VGPS carnivore material is a partial and middle Pleistocene, whereas C. dirus lived during the left m1 (DMNH EPV.63747) and a left metatarsal Late Pleistocene; all other taxa are extant (Nowak 1979). (DMNH EPV.63746), both collected from locality 4086 Various subspecies have been assigned, but we consider in stratigraphic deposits near the mammoth remains. identification of VGPS material only to the species level. The metatarsal DMNH EPV.63746 is not diagnostic Canis rufus has a debated classification within Canidae, enough to merit accurate classification beyond Car- considered by some to be a hybrid between C. latrans and nivora, although subjective comparisons to modern C. lupus (Wayne & Jenks 1991, vonHoldt et al. 2011), and specimens give it a size range compatible with medium a distinct species by others (Wilson et al. 2000, Chambers to large Canis or other similar-size Carnivora. The m1 et al. 2012). Because previous studies have designated C. DMNH EPV.63747 has a fragmentary buccal surface, rufus fossils as distinct from C. lupus and C. latrans (e.g., but a distinct paraconid, protoconid, and talonid basin Nowak 1979), we consider it a distinct fossil morphotype are visible, preserving the base of the crown and the and refer to it as C. rufus. Canids are identified most easily majority of the buccal surface. The specimen from the from fossil material based on size and cranial morphology, VGPS measures 35.66 mm mesiodistally and 12.68 mm with Canis being the largest Pleistocene member in North buccolingually at the enamel base. The length of the America. When complete cranial elements are not avail- m1 is easily within the range of C. dirus and is larger able, dental dimensions and occlusal morphology may be by a considerable margin (>3.5 mm) than the largest used for identification of some canids and Canis species measurements of C. lupus and C. armbrusteri taken (Nowak 1979, Brannick 2014). The m1 (Fig. 17) is mor- by Nowak (1979) (Fig. 18). phologically similar between larger members of the genus Buccolingual measurements are not provided Canis (C. dirus, C. armbrusteri, and C. lupus), although by Nowak (1979), but the VGPS canid molar width is C. dirus has a notably more robust build and considerably comparable to other C. dirus measurements provided larger dimensions in the m1 than other Canis species (Fig. by others (Berta 1988) and those of C. dirus DMNH 18). Size ranges may overlap between smaller C. dirus and specimens. Keeping the fragmentary condition of the larger C. lupus and C. armbrusteri (Nowak 1979). specimen in mind, we propose an identification of

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closely fits the mean length for C. dirus. We consider this identification appropriate given the morphology of the specimen, which is also similar to that of C. dirus. DMNH EPV.63747 represents the first reported instance of Canis dirus from Colorado.

Discussion

On the Significance of Brachylagus idahoensis The discovery of phenotypically modern Brachylagus idahoensis (pygmy rabbits) in Pleistocene deposits of Colorado is important for three reasons: (1) it is the first osteological and fossil evidence of this species in the state, and as such represents an increase in the species’ historic range; (2) given the specific habitat requirements of the species, its presence here strongly suggests a sagebrush-dominated ecosystem present in the northern San Luis Valley during the Late Pleis- tocene, with precipitation and temperatures roughly comparable to those found in modern Brachylagus ranges; and (3) VGPS B. idahoensis specimens provide the nearest geographic occurrence of the genus to Porcupine Cave, where the most complete and holotype remains of B. coloradoensis were discovered. Brachylagus idahoensis is currently restricted to the Great Basin and a small part of eastern Washing- ton, limited largely by the presence of big sagebrush (Green & Flinders 1980, Chapman & Flux 1990, Lyman 2004, Oliver 2004, Grayson 2006, Lee 2008, Rickart et al. 2008, Wilson 2010, Lawes 2012). In the past, Figure 17. Villa Grove Paleontological Site Brachylagus is thought to have survived farther south Canis dirus left first lower molar (DMNH and west than it does currently (Green & Flinders 1980; EPV.63747). (A) Lingual view. (B) Buccal view. Campbell et al. 1982; Grayson 1983, 1985; Prichett (C) Occlusal view. Scale = 50 mm. et al. 1987; Streubel & Fitzgerald 1987; Grayson 1988; VGPS specimen DMNH EPV.63747 as Canis dirus on Harris 1990, 1993; Ramos 1999a; Lyman 2004; Oliver the basis of greater size and morphological similarity 2004; Grayson 2006). The paleontological record of to that than any of the other described Canis species Brachylagus shows a trend toward a declining range in North America. Although we accept there is varia- and increasing latitude since the start of the Holocene tion in the measurements of m1 length in larger Canis (Grayson 1988, 2006). The Late Pleistocene saw rapid species, the particularly large size of the VGPS molar climate shifts ~14,500 to 11,500 14C years BP that is anomalistic for C. lupus or C. armbrusteri and culminated in an overall increase in temperature and

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Figure 18. Weighted average lengths of lower first molar in samples of North American canids adapted from Nowak (1979). Outermost bounds represent the smallest and largest measures of individuals in the data used, and the boundaries of the boxes represent the standard deviation from the mean of the sample measurement. Modern (recent) and fossil male and female specimens are used. Measurements taken from the Denver Museum of Nature & Science zoological and paleontological records of C. lupus and C. dirus had no impact on the range or average values. The Villa Grove specimen is DMNH EPV.63747. All measurements are in millimeters. a disruption of the glacial–interglacial cycles that had temperatures increased and precipitation decreased dominated the North American climatic regime for the (Oliver 2004, Grayson 2006, Swanson 2011). In some previous 100,000 years (Walker et al. 2009). Around this areas with relatively continuous late-Pleistocene time, the western United States experienced a decrease strata, such as at Gatecliff Shelter, Homestead Cave, in sagebrush and sagebrush-dependent taxa ranges and and Danger Cave, this decline is concurrent locally population densities, continuing into the present day with other climate change indicators, such as pinyon– (Grayson 2006). juniper woodland encroachment and the appearance Among these taxa, Brachylagus is noted as of xeric-adapted faunas indicating saltbush replace- having ranged far farther south and east than is seen ment of sagebrush (Oliver 2004, Grayson 2006, today, at least since the Irvingtonian (Miller 1976, Swanson 2011). Some of the study sites that indicate Green & Flinders 1980, Grayson 1983, Heaton 1985, disappearance of sagebrush show later resurgence; Prichett et al. 1987, Harris 1990, 1993, Ramos 1999a, however, Brachylagus fossils do not necessarily follow Baxter 2004, Oliver 2004, Murray et al. 2005, Grayson a similar trend (Grayson 2006, Swanson 2011). From 2006, Swanson 2011; also see Fig. 19). The decline the regression of the Brachylagus range through the in Brachylagus in general appears to coincide with Holocene, and evidence from sites with stratigraphic the end of the Pleistocene, particularly in areas where records through this time period, climate seems likely

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to have played a significant role in the disappearance of (Artemisia tridentata), and is considered sensitive Brachylagus in the southwestern United States. to degradation or loss of sagebrush habitat (Green Modern Brachylagus is found almost exclu- & Flinders 1980, Weiss & Verts 1984, Grayson 1985, sively in areas containing patches of big sagebrush Chapman & Flux 1990, Katzner et al. 1997, Gabler

Figure 19. Map of Brachylagus fossil distributions based on Miller (1976), Grayson (1985), Heaton (1985), Harris (1990), Bell (1995), Ramos (1999a), Oliver (2004), Murray et al. (2005), Grayson (2006), Graham & Lundelius (2010), and this article. Light-gray dots (A, B) represent sites containing B. coloradoensis. Black dots (1–48) represent sites containing B. idahoensis. Note that fossil occurrences in Colorado, Arizona, and New Mexico are well outside of the taxon’s modern range. Site Key: A, Porcupine Cave; B, Cathedral Cave; 1, Villa Grove Paleontological Site; 2, 45AD2; 3, Lind Coulee; 4, Kennewick Roadcut; 5, Miller; 6, Fort Rock Cave; 7, Connley Cave; 8, Hanging Rock Shelter; 9, Last Supper Cave; 10, Dirty Shame Rockshelter; 11, James Creek Shelter; 12, Ezra's Retreat; 13, Deer Creek Cave; 14, Wilson Butte Cave; 15, Veratic Rockshelter; 16, Jaguar Cave; 17, Duck Point; 18, American Falls Reservoir; 19, Rainbow Beach; 20, Moonshiner; 21, Middle Butte Cave; 22, Owl Cave; 23, Serendipity Cave; 24, Danger Cave; 25, Homestead Cave; 26, Hogup Cave; 27, Rock Springs Shelter; 28, Silver Creek; 29, Triple T Shelter; 30, Gatecliff Shelter; 31, Toquima Cave; 32, Slivovitz Shelter; 33, Owl Cave 1 and 2; 34, Crystal Ball Cave; 35, Smith Creek Canyon Packrat Middens; 36, Tule Springs; 37, O’Malley Shelter; 38, Conaway Shelter; 39, Civa Shelter II; 40, Isleta Cave No. 2; 41, Sheep Camp Shelter; 42, Dry Cave New Mexico; 43, Pit Stop Quarry Arizona; 44, Kokoweef Cave California; 45, Camels Back Cave; 46, Hidden Cave; 47, Screaming Neotoma Cave; 48, Lake San Augustine.

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2001, Oliver 2004, Grayson 2006, Lee 2008, Rickart in turn interact with sagebrush growth. The conditions et al. 2008). Recent B. idahoensis declines are often pygmy rabbits favor are not uniformly present in the San attributed to habitat fragmentation (Chapman & Flux Luis Valley, as sagebrush density and snowfall are gener- 1990). Other factors suggested to have a prominent ally less than they are in the Great Basin whereas winter impact on pygmy rabbit ranges include total sagebrush temperatures are higher. Because modern B. idahoensis density, plant height, soil conditions, winter tempera- is dependent upon high-density sagebrush ecosystems, ture, and effective precipitation. and fossil specimens also seem to follow a pattern of co- Lawes et al. (2012) reported a positive impact occurrence with sagebrush (Grayson 2006), its presence of close-proximity large patches of sagebrush to in the fossil record of the VGPS indicates that environ- Brachylagus survival in translocation experiments, and mental conditions associated with the modern species’ Lee (2008) found Brachylagus site use correlated posi- range would have been present in the San Luis Valley tively with continuous rather than isolated patches at during the Late Pleistocene. Paleoclimate data suggesting her study sites, although Lawes et al. (2012) also noted the Late Pleistocene of central Colorado was character- that habitat fragmentation does not impede the rabbits’ ized by temperatures averaging 10 to 13°C cooler than movement severely. Density and height of sagebrush today (Leonard 1989) support this conclusion. tend to correlate positively with Brachylagus popula- The only other site currently known in Colorado to tion densities, which is likely related to the animal’s diet contain Brachylagus fossils is Porcupine Cave, located dependence on the plant, especially during the winter north of Villa Grove in the South Park Basin. The fossils (Green & Flinders 1980, Chapman & Flux 1990, Gabler were designated initially by Barnosky & Rasmussen 2001). Sagebrush also contributes to burrow construc- (1988) as Brachylagus (=Sylvilagus) idahoensis, but tion and cover (Green & Flinders 1980, Chapman & Ramos (1999a) considered them to have morphological Flux 1990, Gabler 2001, Grayson 2006). Soil depth, characters sufficient to warrant the new species: B. colo- texture, and moisture affect sagebrush growth and radoensis. Ramos (1999a) designated all identifiable Brachylagus burrow construction, with the species Brachylagus remains at Porcupine Cave as B. colora- favoring loose fluvial soils at least 0.5 m deep (Green doensis (Baxter 2004), noting the remains were variable & Flinders 1980, Weiss & Verts 1984, Katzner & Parker morphologically and, in some instances, trended toward 1997, Gabler 2001, Lee 2008, Wilson 2010). the morphotype seen in B. idahoensis. The Porcupine The impact of temperature and climate on Cave specimens are Irvingtonian in age, estimated to Brachylagus is not as well studied as other factors be a minimum of around 780,000 years BP (Ramos potentially affecting its range, although the species is 1999a), predating all other known Brachylagus remains cold-weather adapted in both behavior and physiology by serval hundred thousand years. The VGPS specimens (Katzner et al. 1997). Pygmy rabbits are estimated to represent the geographically closest Brachylagus to withstand winter temperatures of -26° to 9°C in their Porcupine Cave, suggesting either a long history of native range, although direct cold exposure is mediated by Brachylagus in the region or multiple instances of burrow systems and snow cover, which provide insulation Brachylagus occupation and subsequent extirpation. (Katzner & Parker 1997, Katzner et al. 1997). Katzner & Other sagebrush-dependent taxa at the VGPS, Parker (1997) found high rates of snow accumulation particularly Lemmiscus curtatus (sagebrush voles) provided better insulation and access to food, and tall and possibly Urocitellus sp. (Urocitellus-clade ground vegetation of the type favored for burrows also tends to squirrel), lend support to the idea that the environment exacerbate the development of larger snow drifts. at the VGPS was a sagebrush-dominated ecosystem Brachylagus habitat suitability is likely not solely similar to that of the modern Great Basin, where these dependent upon the presence or density of sagebrush, but taxa co-occur. Presence of sagebrush-dependent species also on soil structure and snow accumulation, which may at multiple strata at the VGPS suggest these conditions

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may have been met for some extended period of time Like Brachylagus, the genus Lemmiscus is during the Late Pleistocene. At some point, likely by documented farther south and east in late-Pleistocene the end of the Pleistocene or early Holocene, sagebrush deposits than the borders of its current range (Carroll density diminished to its current occurrence within & Genoways 1980, Grayson 1983, Emslie 1986, Harris the San Luis Valley and sagebrush-dependent species 1990, Bell & Glennon 2003, Barnosky & Bell 2003). became extinct locally. The records of the VGPS supply Lemmiscus is also found in regions dominated by important data for pygmy rabbit conservation and sagebrush, which it uses primarily as cover and for food support other paleontological evidence that this taxon (Carroll & Genoways 1980). It is less strictly dependent was found previously at much lower latitudes and over upon sagebrush than Brachylagus, ranging farther and a larger range than it occupies currently. surviving in loosely connected patches (Bell & Glennon 2003). Lemmiscus often appears in Pleistocene sites Paleoecological Context that formerly experienced higher winter precipitation The faunal composition of the VGPS provides informa- rates than they do currently (Carroll & Genoways 1980, tion about the surrounding paleoecological system, Harris 1990, Bell & Glennon 2003). particularly in ecologically sensitive faunas, but also Urocitellus does not occur in this part of Colo- in the makeup of its communities. Late-Pleistocene rado, although the genus occurs in northern Colorado vertebrate assemblages in North America are noted for and is represented by the species U. elegans (Zegers having larger numbers and greater diversity of mega- 1984). Although the VGPS material was insufficiently fauna than those that currently exist on the continent, distinct to derive species identification, the specimens whereas microvertebrate compositions often bear a bore a closest resemblance in size and dental morphol- close resemblance to extant communities. Sympatry ogy to U. richardsonii, U. elegans, and U. beldingi, between any given fossils found at the site is unclear, and also some similarity to U. townsendii, U. mollis, but the presence of Brachylagus idahoensis at mul- and U. canus. Of these species, U. elegans, U. beldingi, tiple strata in both localities suggests continuity in local U. townsendii, U. mollis, and U. canus are found in paleoecology over the course of site deposition, given sagebrush-rich environments in the Great Basin and the species’ noted habitat restrictions. occur within the ranges of Brachylagus and Lemmis- Canis dirus (dire wolf), Brachylagus idahoensis, cus, in sagebrush habitats (Carroll & Genoways 1980, Lemmiscus curtatus, and Urocitellus all have limited Green & Flinders 1980, Jenkins & Eshelman 1984, Zegers or absent records in Colorado (Nowak 1979, Koeppl & 1984, Rickart 1987, Helgen et al. 2009). U. richardsonii Hoffman 1981, Dundas 1999, Grayson 2006, Helgen et occurs in arid grassland environments northward into al. 2009, Ramos 1999a). parts of Canada (Michener & Koeppl 1985). The uncer- Lemmiscus curtatus and the genus Urocitellus tainty in identification of Urocitellus at the VGPS and are not currently found in the San Luis Valley, and are the broader range of other members of the genus limit restricted to northern Colorado (Carroll & Genoways its paleobiogeographic significance here. Further study 1980), although they have often been found farther of Urocitellus fossil distributions may clarify this taxon’s south in the fossil record (Harris & Findley 1964; ecological utility in fossil assemblages. Carroll & Genoways 1980; Zegers 1984; Michener & The taxa Cynomys gunnisoni, Lepus, and Syl- Koeppl 1985; Emslie 1986; Rickart 1987; Harris 1990, vilagus nuttallii are all currently present in the San 1993; Barnosky & Bell 2003; Bell & Glennon 2003; Luis Valley as native residential taxa found historically Murray et al. 2005). Canis dirus does not have any in Colorado. Cynomys, Lepus, and Sylvilagus are found known record in Colorado, although it is known from throughout the state, although C. gunnisoni is more every surrounding state (Nowak 1979, Kurtén & Ander- restricted in range to west of the continental divide and son 1980, Dundas 1999, Morgan & Lucas 2006). south of C. leucurus ranges (Keen 1971, Pizzimenti &

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Hoffmann 1973). S. nuttallii is generally found in the among the VGPS faunas. Its occurrence this far into western two thirds of the state (Chapman 1975). Bison the San Luis Valley without prior occurrence elsewhere were common in plains ecosystems throughout North in the region is somewhat surprising, but not unprec- America until recently, including in the San Luis Valley. edented given its large range and presence near the Ecological contributions of extinct taxa may only Colorado border of New Mexico (Morgan & Lucas 2005). be inferred based on their functional morphologies and The combination of plains grazing animals, geological context, but the co-occurrence of modern traditionally arid-environment western taxa including and extinct taxa at late-Pleistocene sites such as the Cynomys and S. nuttallii, and sagebrush-dependent VGPS offer some insight into some of the possible paleo- species indicate that the VGPS retained a similar overall ecological contributions of extinct megafauna. structure to its current ecosystem, but likely with a Mammuthus columbi was adapted to a varied greater sagebrush density and more prominent mega- diet according to dental morphology and residue studies fauna. Geological evidence points to fluvial activity in the and may have been a grazer, browser, or both depend- initial formation of the deposits, with subsequence cessa- ing on its local environment (Rivals et al. 2012). Extinct tion and later flooding events occurring at least during Camelops and Equus are also interpreted to have been the time when the mammoth bones were interred. Fluvial common grazers throughout plains environments of deposits would have been favorable to burrowing animals North America in the Pleistocene, able to survive in a such as Cynomys, Urocitellus, and Brachylagus, some of variety of habitats occupying a range of temperatures which occurred in filled burrows. Given the small size of and weather patterns based on their widespread fossil the site and its limited preservation of invertebrate and record. Mammuthus columbi, Equus, and Camelops plant remains, late-Pleistocene deposits in the northern are present at the Ziegler Reservoir Fossil Site, but lived San Luis Valley would be worth exploring further to refine in a far wetter, more densely forested environment than our understanding of end-Pleistocene local climatic shifts that indicated at the VGPS (Miller et al. 2014, Sertich et and their ecological impact. al. 2014). Equus and Camelops also both occur in the older, more arid Porcupine Cave site (Mead & Taylor 2004, Scott 2004). All these megafauna are known to have largely gone extinct in North America by the end of the Pleistocene, likely in response to climatic change, possibly in association with other factors such as human hunting pressures (Barnosky 2004). Their relationship to sagebrush environments is poorly understood. Canis dirus was one of a handful of large North American predators present throughout the Late Pleis- tocene (Kurtén & Anderson 1980, Dundas 1999). It has never been recorded in Colorado deposits, but is known from numerous sites in surrounding states, including one near the Colorado border with New Mexico (Morgan & Harris 2015). It is thought to have occupied a wide range of habitats, including plains, highlands, and several types of forests from the western to the eastern coast of the continent and down into parts of South America (Dundas 1999). The C. dirus remains are noteworthy in that they represent a higher trophic level

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Acknowledgments References Cited We thank Paul and Harriet Rosen for their support Agenbroad, L., Morris, D., & Roth, L. 1999. Pygmy mam- funding the site excavation, and the U.S. Department moths Mammuthus exilis from Channel Islands of the Interior Bureau of Land Management Colorado National Park, California (USA). Pp. 89–102. in Division, particularly Harley Armstrong, for facilitating Haynes, G., Klimowicz, J. & Reumer, J.W.F. (ed.): site research (permit no. COC74333). We also thank the Mammoths and the Mammoth Fauna: Studies of 2011 and 2012 DMNS Paleontology Teen Science Schol- an Extinct Ecosystem. Rotterdam, Netherlands: ars who were closely involved in the site excavations and Deinsea. microvertebrate picking. We extend a special thanks to Averianov, A.O., Abramov, A.V., & Tikhonov, A.N. 2000. A Charles Nelson for his help housing the specimens and new species of Nesolagus (Lagomorpha, Lepori- consulting on the site microvertebrates, and the other dae) from Vietnam with osteological description. DMNS volunteers who helped with cataloguing, housing, Contributions from the Zoological Institute St. and preparation. Thank you to Jeff Stephenson and the Petersburg 3: 1–22. Museum of Vertebrate Zoology at University of California, Barnosky, A.D. 2004. Biodiversity Response to Climate Berkeley, who provided valuable reference material for Change in the Middle Pleistocene: The Porcupine taxa identification. We thank Logan Ivy, Carol Lucking, Cave Fauna from Colorado. Berkley, CA: University Kristen MacKenzie, and David Krause, who were respon- of California Press. xxi, 385 pp. sible for specimen curation. We also thank Jaelyn Eberle, Barnosky, A.D. & Bell, C.J. 2003. Evolution, climatic Sara Oser, Carolyn Levitt-Bussian, Megan Sims, Gary change and species boundaries: Perspectives from Morgan, George Corner, Veronika Hall, and Allie Skaer tracing Lemmiscus curtatus populations through for additional information. Finally, we thank the editor, time and space. Proceedings of the Royal Society James Hagadorn, and the three anonymous reviewers for of London B 270: 2585–2590. their help improving this manuscript. Barnosky, A.D. & Rasmussen, D.L. 1988. Middle Pleis- tocene arvicoline rodents and environmental change at 2900-meters elevation, Porcupine Cave, South Park, Colorado. Annals of Carnegie Museum 57: 267–292. Baxter, C.N. 2004. Leporidae of the DMNH Velvet Room excavations and Mark’s Sink. Pp. 164–168 in Bar- nosky, A.D. (ed.): Biodiversity Response to Climate Change in the Middle Pleistocene: The Porcupine Cave Fauna from Colorado. Berkeley, CA: Univer- sity of California Press. Behrensmeyer, A.K. 1978. Taphonomic and ecologic information from bone weathering. Paleobiology 4 (2): 150–162. Bell, C.J. & Glennon, J. 2003. Arvicoline rodents from Screaming Neotoma Cave, Southern Colorado Plateau, Apache County, Arizona, with comments on the Pleistocene biogeography of Lemmiscus curtatus. Pp. 54–63 in Schubert, B.W., Mead, J.I., & Graham, R.W. (eds.): Ice Age Cave Faunas of North America. Bloomington, IN: Indiana University Press.

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Cover photo: Denver Museum of Nature and Science Curator of Paleoecology Dr. Richard Stucky and students from the 2011 Teen Science Scholars program excavating mammoth bones at Locality 4086 of the Villa Grove Paleontological Site. From left to right: Emily Hoefs; Olivia Verma; Evan Alger-Meyer; Richard Stucky; Ashley Goodfellow; Clara Miller; Orion Hunter. Photo: Steven Holen, July 14, 2011.

The Denver Museum of Nature & Science Annals is an Frank Krell, PhD, Editor-in-Chief The Pleistocene Mammalian Fauna open-access, peer-reviewed scientifi c journal publishing and Paleoenvironment of the EDITORIAL BOARD: original papers in the fi elds of anthropology, geology, James Hagadorn, PhD (subject editor, Paleontology and paleontology, botany, zoology, space and planetary Villa Grove Paleontological Site, Geology) sciences, and health sciences. Papers are either authored Colorado Nicole Garneau, PhD (subject editor, Health Sciences) by DMNS staff, associates, or volunteers, deal with DMNS John Demboski, PhD (subject editor, Vertebrate Zoology) specimens or holdings, or have a regional focus on the Steve Lee, PhD (subject editor, Space Sciences) Rocky Mountains/Great Plains ecoregions. Evan Alger-Meyer, Frank Krell, PhD (subject editor, Invertebrate Zoology) Jared Maxwell Beeton, The journal is available online at www.dmns.org/science/ Steve Nash, PhD (subject editor, Anthropology and Richard K. Stucky, and publications/dmns-annals free of charge. Paper copies are Archaeology) Steven R. Holen available for purchase from our print-on-demand publisher

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