ALBERT

Description: A new species of mastodon from the Pleistocene of western North America, Mammut pacificus sp. nov. is herein recognized, with specimens identified throughout California and from two localities in southern Idaho. This new taxon differs from the contemporaneous M. americanum in having narrower teeth, most prominently in M3/m3, as well as six sacral vertebrae, femur with a proportionally greater mid-shaft diameter, and no mandibular tusks at any growth stage. All known Pleistocene Mammut remains from California are consistent with our diagnosis of M. pacificus, which indicates that M. americanum was not present in California.

Description: Late Pleistocene groundwater discharge deposits (paleowetlands) in the upper Las Vegas Wash north of Las Vegas, Nevada, have yielded an abundant and diverse vertebrate fossil assemblage, the Tule Springs local fauna (TSLF). The TSLF is the largest open-site vertebrate fossil assemblage dating to the Rancholabrean North American Land Mammal Age in the southern Great Basin and Mojave Desert. Over 600 discrete body fossil localities have been recorded from the wash, including an area that now encompasses Tule Springs Fossil Beds National Monument (TUSK). Paleowetland sediments exposed in TUSK named the Las Vegas Formation span the last 250 ka, with fossiliferous sediments spanning ∼100–13 ka. The recovered fauna is dominated by remains ofCamelopsandMammuthus, and also includes relatively common remains of extinctEquusandBisonas well as abundant vertebrate microfaunal fossils. Large carnivorans are rare, with onlyPuma concolorandPanthera atroxdocumented previously. Postcranial remains assigned to the speciesCanis dirus(dire wolf) andSmilodon fatalis(sabre-toothed cat) represent the first confirmed records of these species from the TSLF, as well as the first documentation ofCanis dirusin Nevada and the only known occurrence ofSmilodonin southern Nevada. The size of the recovered canid fossil precludes assignment to other Pleistocene species ofCanis. The morphology of the felid elements differentiates them from other large predators such asPanthera,Homotherium, andXenosmilus, and the size of the fossils prevents assignment to other species ofSmilodon. The confirmed presence ofS. fatalisin the TSLF is of particular interest, indicating that this species inhabited open habitats. In turn, this suggests that the presumed preference ofS. fatalisfor closed-habitat environments hunting requires further elucidation.