Jim I. Mead

Late Quaternary environments and biogeography in the Great Basin

Abstract Plant and animal remains found in packrat ( Neotoma spp.) middens and cave fill from the eastern and southern Great Basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the Late Wisconsin. Limber pine ( Pinus flexilis ) and bristlecone pine ( P. longaeva ) were important in the late Pleistocene plant communities throughout this region. Spruce ( Picea cf. engelmannii ) and common juniper ( Juniperus communis ) were present in some of the more northerly localities, and Douglas fir ( Pseudotsuga menziesii ) and white fir ( Abies concolor ) were present in southern and eastern localities. Single needle pinyon pine ( Pinus monophylla ), common across this region today, was apparently not present north of the Sheep Range of southern Nevada during the Late Wisconsin. Pikas ( Ochotona cf. princeps ), small boreal mammals present in only a few Great Basin mountain ranges today, were common throughout the region. Heather voles ( Phenacomys cf. intermedius ) have been found in two cave fill deposits in Nevada, though they are unknown in the Great Basin today. Limber and bristlecone pines are generally restricted to rocky substrates in modern subalpine habitats in the Great Basin, and this may also have been the case when these plants grew at lower elevations during the Late Wisconsin. Subalpine conifers were present on the rock outcrops sampled by the packrat middens, but shrub communities, perhaps dominated by sagebrush ( Artemisia spp.), may have been present on alluvial valley-bottom substrates. Forested habitats would thus have been isolated habitat islands, as they are today. Boreal small mammals, including pikas and heather voles, were able to colonize the Great Basin mountain ranges during the late Pleistocene. We suggest that these mammals were able to survive in the intervening valley-bottoms under a cool-summer climatic regime, and that continuous forest or woodland corridors were not necessary for migration.

Middle- and late-Wisconsin paleobotanic and paleoclimatic records from the southern Colorado Plateau, USA

The Colorado Plateau is a distinct physiographic province in western North America, which presently straddles the transition between summer-wet and summer-dry climatic regimes to the south and northwest, respectively. In addition to climate, the diversity of environments and plant communities on the Colorado Plateau has resulted from extreme topographic diversity. Desert lowlands as low as 360 m elevation are surrounded by forested plateaus, and even higher peaks greater than 3800 m elevation. This environmental diversity provides a unique opportunity to study the history of biotic communities in an arid region of North America. Although the Colorado Plateau harbours numerous potential sites, the paleoecological record of the Plateau is poorly known. Potential deposits for analysis include packrat middens, alluvial and cave sites at lower elevations, and lake, bog and wetland sites at higher elevations. Forty-six sites have been analysed across the nearly 337,000 km2 region, of which 27 contain records that span Marine Oxygen Isotope Stage (IS) 2 data, with IS 3 information coming from only 12 sites. Most IS 2 and 3 sites are clustered along the lowland regions of the Colorado River corridor and the uplands of the Mogollon Rim area. We compiled selected data from long paleoecological records to examine patterns of vegetation and climate change across the southern Colorado Plateau for the middle and late Wisconsin. During the middle Wisconsin, mixed conifers covered middle-elevations presently dominated by ponderosa pine (Pinus ponderosa), and juniper (Juniperus) woodland grew at elevations today covered by blackbrush (Coleogyne) and sagebrush (Artemisia) desert. During the late Wisconsin, boreal conifers, primarily Engelmann spruce (Picea engelmannii), replaced the mixed conifer association. Estimates of mean annual temperatures (MAT) during IS 3 were at least 3–4°C cooler than today, whereas IS 2 MAT estimates are at least 5°C colder. Our investigation of millennial-scale climatic variability within the region provided equivocal results. The packrat midden sequence could not distinguish vegetation changes that might be associated with Heinrich events in the North Atlantic. From the lake records, however, many Heinrich events were associated with generally drier intervals, often with elevated sagebrush pollen concentrations. Future paleoecological investigations should concentrate on the northern Colorado Plateau, as well as the eastern and western margins. Additional sites, along with closer-spaced sampling in regions already studied, will be important in determining the history of important climatic phenomena such as the timing of the Arizona monsoon.

The timing of Late Pleistocene mammalian extinctions in North America

More than 375 14C dates from 150 fossil sites in North America have been analyzed to evaluate the question of extinction of Late Pleistocene megafauna. When critically evaluated, no 14C ages for any extinct Pleistocene genera are younger than 10,000 yr B.P.

Dung of Mammuthus in the arid Southwest, North America

Abstract The discovery of a unique organic deposit in a dry cave on the Colorado Plateau, southern Utah, permits the first comparison of the physical characteristics and the diet of the dung of the extinct mammoths from the arid Southwest, North America, with that of mammoths from Siberia and northern China, the only other known locations of such remains. The deposit buried beneath sand and rockfall is composed primarily of mammoth dung, estimated at over 300 m3. Radiocarbon dates on dung boluses indicate that the mammoths frequented the cave between approximately 14,700 and 11,000 yr B.P. (the range of ages at 2σ). The desiccated boluses, measuring approximately 230 × 170 × 85 mm, are nearly identical in size to dung from extant elephants. The largest contents in the dung are stalks measuring 60 × 4.5 mm. Grasses and sedges dominated the diet, although woody species were commonly eaten.

New Extinct Mekosuchine Crocodile from Vanuatu, South Pacific

Abstract We describe a new species of crocodile (Reptilia: Crocodyloidea: Mekosuchinae) from a maxilla recovered at the Arapus archaeological site, on the island of Efate, Vanuatu, South Pacific. As with mekosuchine species in New Caledonia and Fiji, Mekosuchus kalpokasi sp. nov. was a small, possibly terrestrial carnivore that is now extinct. The differences between the Efate specimen and previously described species of Mekosuchus warrant recognition of a new species. Based on its association with Efates earliest known human inhabitants, dating approximately 3000 cal yr B.P., the extinction of M. kalpokasi and other insular mekosuchines may have been anthropogenic. The lack of adequately dated pre-Quaternary and Quaternary vertebrate fossil records from Vanuatu, New Caledonia, and Fiji (as well as other smaller islands) precludes determining the timing and route of dispersal of mekosuchine crocodyloids.

TROPICAL MARSH AND SAVANNA OF THE LATE PLEISTOCENE IN NORTHEASTERN SONORA, MEXICO

Abstract We recovered Pleistocene fossils from a lava-dammed river deposit along the Río de Moctezuma in northeastern Sonora, at 29°41′N, 109°39′W, and 605 m elevation. Today the region is semiarid, with a foothills thornscrub community. The impoundment that resulted from the lava dam produced a short-lived marsh with an adjacent savanna. The extraordinary fauna is both diverse and rich, and includes ostracods, mollusks, fish, amphibians, turtles, a crocodilian, snakes, lizards, birds, and mammals, many with tropical affinities today. Most of the animals are either extralimital to the setting today or extinct. The recovery of Bison dictates a Rancholabrean Land Mammal Age for the fauna; a preliminary 40Ar/39Ar age suggests that the deposit is between 570,000 and 310,000 years old. The occurrence of cf. Crocodylus acutus (a crocodilian; generic assignment uncertain) and Pampatherium, the giant armadillo, is unique in the northern interior Sonora setting. We speculate that a well-developed riparian corridor along the Río Yaqui, from the Gulf of California to the mountain-valley setting at Térapa, permitted the animals with tropical affinities to extend 350 km inland.

Not Enough Skeletons in the Closet: Collections‐Based Anatomical Research in an Age of Conservation Conscience

The emergence of new technologies and improved computing power helped to introduce a renewed vitality in morphological research in recent decades. This is especially apparent in the new advances made in understanding the evolutionary morphology of the skeletal system in extinct and extant squamate reptiles. The new data generated as a result of the recent increase in attention are relevant not only for systematic analyses but also are valuable in their own right for contributing to holistic perspectives on organismal evolution, mosaic evolution in the rates of change in different anatomical systems, and broader patterns of macroevolution. A global community of morphological researchers now can share data through online digital collections, but opportunities for continued advance are hindered because we lack even basic data on patterns of variation of the skeletal system for virtually all squamate lineages. Most work on skeletal morphology of squamates is based on a sample size of n = 1; this is an especially noticeable phenomenon for studies relying on X‐ray computed tomography technology. We need new collections of skeletal specimens, both material and digital, and new approaches to the study of skeletal morphology. Promising areas for continued research include the recent focus on skeletal elements not traditionally included in morphological studies (especially systematic analyses based upon morphological data) and efforts to elucidate patterns of variation and phylogenetically informative features of disarticulated skeletal elements. Anat Rec, 297:344–348, 2014.

Extinct mountain goat (Oreamnos harringtoni) in Southeastern Utah

The extinct Harringtons mountain goat (Oreamnos harringtoni Stock) is predominantly known from dry cave localities in the Grand Canyon, Arizona, in addition to two sites in the Great Basin, Nevada, and from San Josecito Cave, Nuevo Leon, Mexico. A dry shelter in Natural Bridges National Monument, on the central Colorado Plateau, southeastern Utah, preserves numerous remains of the extinct mountain goat in addition to pack rat middens. Remains from a 100-cm stratigraphic profile indicate that O. harringtoni lived on the plateau >39,800 yr B.P., the oldest directly dated find of extinct mountain goat. Plant macrofossils indicate that Engelmanns spruce (Picea engelmannii), limber pine (Pinus flexilis), rose (Rosa cf. woodsii), and Douglas fir (Pseudotsuga menziesii) grew during the late Pleistocene where a riparian and a pinyon-juniper (Pinus edulis-Juniperus osteosperma) community now predominates; Douglas fir are found only in mesic, protected, north-facing areas. Limber pine, Douglas fir, bark, and grasses were the major dietary components in the dung. A springtime diet of birch (Betula) is determined from pollen clumps in dung pellets.

Late Pleistocene Reptiles and Small Mammals from the Lower Grand Canyon of Arizona

Twenty-one taxa and 130 identifiable specimens of reptiles and small mammals preserved in late Pleistocene packrat middens from the lower Grand Canyon of Arizona were identified. Samples range in age from 8540 + 180 to 16,330 ?- 270 radiocarbon years. Plant macrofossils of approximately 75 species are associated with the fauna. The plants are a mixture of present desert forms and woodland species (Juniperus sp., Fraxinus anomala, Ribes montigenum) now restricted to higher elevations on the rims of the Grand Canyon. The fauna also represents a mixture of present desert species (Gopherus agassizi, Sauromalus obesus, Coleonyx variegatus) and higher woodland species (Sceloporus undulatus or occi- dental is Neotoma mexicana, Erethizon dorsatum, Marmota flaviventris). Mixed biotic communities in the Pleistocene may reflect a more moderate climate which had mild winters, cool summers, and slightly increased winter rainfall. Rampart Cave in the lower Grand Canyon of Arizona is best known for its remarkable late Pleistocene deposit of dung of the extinct Shasta ground sloth, Nothrotheriops shastense (Laudermilk and Munz 1938; Martin, Sabels and Shutler 1961; Long and Martin 1974). The dung deposit contains large quantities of well-preserved plant and animal remains that provide a record of late Pleistocene biotic com- munities. Wilson (1942) published a preliminary faunal analysis from Rampart Cave principally concerned with large extinct mam- mals. Our analysis is of reptiles and small mammals represented in the samples collected from this cave and nearby areas. In addition to the sloth dung deposit, Rampart Cave is a rich source of Pleistocene packrat (Neotoma) middens. Middens have been found within the cave both associated with the sloth dung deposit, and inde- pendent from it. Additional middens have been collected from num- erous localities within 3 km of the cave, from side canyons and from open sites on both sides of the Colorado River (Phillips and Van

Vertebrate community on an ice-age Caribbean island

Significance A flooded sinkhole cave on Abaco (The Bahamas) has yielded the richest (95 species) set of late Pleistocene (ice-age) vertebrates on any Caribbean island. We track changes in species composition on Abaco through time and relate those biotic changes to climate change. The warmer, wetter climate and rising sea levels from 15,000 to 9,000 years ago probably led to the disappearance on Abaco of at least 17 species of birds. Another 22 species of reptiles, birds, and mammals persisted through those environmental changes but did not survive the last 1,000 years of human activity. For the species that remain, we believe that direct human activity threatens their future more than climate change. We report 95 vertebrate taxa (13 fishes, 11 reptiles, 63 birds, 8 mammals) from late Pleistocene bone deposits in Sawmill Sink, Abaco, The Bahamas. The >5,000 fossils were recovered by scuba divers on ledges at depths of 27–35 m below sea level. Of the 95 species, 39 (41%) no longer occur on Abaco (4 reptiles, 31 birds, 4 mammals). We estimate that 17 of the 39 losses (all of them birds) are linked to changes during the Pleistocene–Holocene Transition (PHT) (∼15–9 ka) in climate (becoming more warm and moist), habitat (expansion of broadleaf forest at the expense of pine woodland), sea level (rising from −80 m to nearly modern levels), and island area (receding from ∼17,000 km2 to 1,214 km2). The remaining 22 losses likely are related to the presence of humans on Abaco for the past 1,000 y. Thus, the late Holocene arrival of people probably depleted more populations than the dramatic physical and biological changes associated with the PHT.