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A fossil giant tortoise from the Mehrten Formation of Northern California

Hesperotestudo is a genus of giant tortoise that existed from the Oligocene to the Pleistocene of North and Central America. Recorded occurrences in the United States are plentiful; however, California seems to be an exception. Literature on Hesperotestudo in California is limited to faunal lists in papers, with few detailed descriptions. Here we review the literature on the genus, describe and identify specimens found in the upper Mehrten Formation (late Miocene-early Pliocene) exposed in the Central Valley of California at Turlock and Modesto Reservoirs, Stanislaus County, and address their implications for early Pliocene California biogeography and climate. All fossils described are from the collections of the University of California Museum of Paleontology (UCMP). The largest specimen from the Mehrten is a peripheral from an animal with an estimated carapace length over one meter. The specimens were compared first to modern material of Gopherus, the only other tortoise genus from the late Miocene-early Pliocene of California, and then to measurements from the literature of the three species of Hesperotestudo to which it could most likely be referred: H. osborniana, H. orthopygia, and H. campester. Based on characteristics and measurements of the carapace and plastron, these specimens are assigned to H. orthopygia. Hesperotestudo orthopygia is a species known primarily from the Great Plains region, so its presence in California during the late Miocene-early Pliocene indicates that it expanded west into California at this time. Large tortoises are not very tolerant of frost conditions, possibly indicating a relatively frost free climate for this area at the time. This agrees with previous estimates of annual temperature records based on plant fossils from the upper Mehrten Formation, in particular the presence of Persea, an avocado relative, which is also frost sensitive.

Western Association of Vertebrate Paleontology Annual Meeting: Program with Abstracts

Abstracts and program for the February 13-14, 2016, WAVP Annual Meeting, Anza-Borrego Desert State Park, Borrego Springs, CA, USA.

Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming

Rodent assemblages are described from two early Eocene (Wasatchian North American Land Mammal Age; Graybullian subage) localities from the Main Body of the Wasatch Formation in the Washakie Basin, Wyoming. One locality (UCMP V71237) represents a catastrophic death assemblage and the other (UCMP V71238) is a channel lag which immediately overlies it. Quarrying and screen-washing at these localities has resulted in the recovery of 81 specimens from V71237 and 224 specimens from V71238 and comprising a uniquely rich, stratigraphically controlled sample. The rodent fauna from these localities include Paramys copei, P. taurus, Lophiparamys murinus, Microparamys hunterae, Tuscahomys ctenodactylops, and Knightomys cf. K. minor. These specimens provide substantial new morphological data for the previously poorly-known M. hunterae, T. ctenodactylops, and L. murinus. Comparison of relative abundances demonstrates that T. ctenodactylops is the most common in both localities, but that the smaller bodied species M. hunterae and Knightomys cf. K. minor are much rarer in the lag deposit.

Yelmochelys rosarioae gen. et sp. nov., a stem kinosternid (Testudines; Kinosternidae) from the Late Cretaceous of Coahuila, Mexico

A small smooth-shelled kinosternoid from the late Campanian Cerro del Pueblo Formation and the early Maastrichtian Canyon del Tule Formation of Coahuila, Mexico that is abundantly represented by isolated elements is described as Yelmochelys rosarioae gen. et sp. nov. A phylogenetic analysis concludes that Y. rosarioae is a representative of the stem lineage of the Kinosternidae. Inclusion of Y. rosarioae in Kinosternidae is supported by presence of a groove for the musk duct, the loss of the eleventh peripheral and twelfth marginal, reduced articulation between the plastron and carapace, and diamond-shaped vertebral scales. A basal position within Kinosternidae is indicated by the presence of distinct abdominal scales that meet at the midline and the presence of a relatively long costiform processes. The inclusion of Y. rosarioae in Kinosternidae supports the hypothesis that Kinosternidae and Dermatemydidae had diverged by the Late Campanian.

Fauna and setting of the Adelolophus hutchisoni type locality in the Upper Cretaceous (Campanian) Wahweap Formation of Utah

We report new data on the type locality of the hadrosaurid ornithischian Adelolophus hutchisoni Gates et al., 2014 from the Campanian-aged Wahweap Formation of southern Utah, and the remainder of the vertebrate assemblage from the site. The type locality (UCMP V98173) is a previously-reported U.S. Geological Survey locality (USGS D815) and is stratigraphically low in the upper member of the Wahweap Formation. Additional taxa from the same site include acipenseriforms (sturgeon), amiiforms (bowfin), and lepisosteiforms (gar fish), baenid and trionychid turtles, and both theropod and ornithischian dinosaurs.

Pleistocene vertebrates of Silicon Valley (Santa Clara County, California)

Here we report on late Pleistocene fossil vertebrates from new and previously described localities in Santa Clara County, California. The three new localities and specimens include: a partial mammoth pelvis from UCMP V91128 (Lawrence Expressway E); a juvenile cranial specimen of Mammuthus columbi from UCMP V99597 (SCVWD “Lupe” Mammoth), now on display at the San Jose Children’s Discovery Center; and a relatively diverse assemblage of medium- to large-sized mammals, including a nearly complete forelimb of Paramylodon harlani from UCMP V99891 (Babcock’s Bones). We also reassess specimens and assemblages from the following eight previously known localities: Molecular Medicine Building (UCMP V90003); Alma Street Underpass at Page Mill Road (USGS M1203); Mountain View Dump (USGS M1227); Sunnyvale Sewer (USGS M1218); Calabaza, Sunnyvale Sewer (USGS M1218A); Matadero Creek (USGS M1001); Matadero Creek, Veteran’s Hospital (USGS M1202); and Milpitas (UCMP V4916). All localities discussed, except Matadero Creek and Veterans Hospital, are mapped in areas with surficial Holocene deposits, and therefore, these Pleistocene-aged assemblages suggest that Pleistocene deposits are closer to the surface in Santa Clara County than may have been previously thought. Material described here highlights the needed resources for mitigation management in Santa Clara County.

First record of the megatoothed shark Carcharocles megalodon from the Mio-Pliocene Purisima Formation of Northern California.

Megatoothed sharks (Family: Otodontidae) are among the most widely reported sharks in Cenozoic marine sediments worldwide, and certain species such as the famed Carcharocles megalodon are particularly abundant in Neogene deposits on the Atlantic margin of the United States. Cenozoic marine strata on the Pacific margin of North America have yielded one of the most densely sampled marine vertebrate records anywhere, but published occurrences of shark assemblages are uncommon. Rarer yet are published occurrences of C. megalodon from this region with unambiguous provenance and robust age control — critical data required for the study of recent marine vertebrate faunal evolution in the eastern North Pacific. A tooth of C. megalodon from near Santa Cruz, California, represents the first record of this species from the Purisima Formation and the geochronologically youngest occurrence (6.9–5.6 Ma, uppermost Miocene; late Messinian) of this species from northern California.

A lower jaw of the nautiloid Aturia angustata (Conrad, 1849) from Oligocene cold seep limestone, Washington State, U.S.A.

Fossil shells of the extinct nautiloid genus Aturia have been found in Cenozoic strata in many parts of the world, and yet there have only been two previous records of fossils of any part of the jaw apparatus of Aturia. This suggests that the jaws were only preserved by virtue of special, highly localized conditions. A fossilized lower jaw referable to Aturia has been found in western Washington State, USA, associated with two shells of Aturia angustata within a piece of limestone that formed as a result of localized hydrocarbon seepage on the deep-sea floor. This is the first report of a nautiloid jaw from Cenozoic strata of western North America, and the first report of any part of the jaw apparatus for A. angustata.

The giant, spike-toothed salmon, Oncorhynchus rastrosus and the “Proto-Tuolumne River” (early Pliocene) of Central California

Oncorhynchus rastrosus was a very large, spike-toothed, Pacific Salmon from the mid-Miocene to early Pliocene of the Pacific Northwest (California to Washington). It had two large premaxillary (breeding-fighting) teeth that stuck out laterally from the snout like spikes. It migrated from the Pacific Ocean to inland rivers to spawn, as extant Pacific salmon do today. It was planktivorous, based on numerous, long, over-lapping gill-rakers, and few, small teeth. There are gaps in our knowledge about this interesting salmon. First, one of the localities where many of the paratype specimens were collected (Turlock Lake, California), was not described geologically in the original paper beyond, ‘from the Mehrten Formation’. Here we describe these deposits as cross-bedded sands, gravels and large, rounded cobbles indicative of a fast-flowing, river, which we coin here as the “proto-Tuolumne River,” that periodically overflowed its banks. Paleocurrent directions indicate the river flowed to the southwest, where it joined the San Joaquin River in the Central Valley and flowed southward at this time (~5 Ma), emptying into a marine embayment near Bakersfield. Thus, the Turlock Lake O. rastrosus specimens would have migrated up from this embayment. Second, we investigated whether O. rastrosus developmentally changed before migration upriver to spawn, as extant Pacific salmon do today, by comparing premaxillary teeth from freshwater and coastal marine deposits in California. We found that the largest teeth (with the largest osseous tooth bases) were from freshwater deposits, and that these specimens had the most worn and blunt tooth tips. We propose that this was due to use in territorial defense during spawning and redd (nesting site) construction.