North American Land Mammal Research Articles

Evidence of early C4 grasses, habitat heterogeneity, and faunal response during the Miocene Climatic Optimum in the Mojave Region

Major changes to landscapes, climate, and mammalian faunas occurred at the regional scale in western North America during the Miocene Climatic Optimum (MCO) between ~17 and 14Ma, but few studies have looked at how the MCO affected basin-scale environments. Paleoenvironmental reconstructions coupled with mammalian fossil assemblages from the Crowder and Cajon Valley formations in the Mojave Desert, California, contribute insights into local-scale (10s of kilometers) responses to warming during the Hemingfordian and Barstovian North American Land Mammal Ages. By integrating lithological descriptions, phytolith analyses, carbon isotope composition of preserved soil organic matter (δ13CSOM), and elemental geochemistry of paleosols, we provide reconstructions of depositional environments, vegetation, and precipitation through the MCO. Phytolith and δ13CSOM evidence suggest that paleoenvironments were predominately C3 grasslands, with the earliest potential presence of C4 grasses in the region found within the Crowder Formation at ~17Ma. Based on elemental geochemistry of paleosols, mean annual precipitation estimates are 807 (±182) mm yr−1 at 17Ma in the Crowder Formation and 740–800 (±182) mm yr−1 from 16 to 15Ma in the Cajon Valley Formation. Our multiproxy approach indicates that the Crowder and Cajon Valley basins were stable, large-scale braided stream and floodplain systems with intermittent paleosol development and heterogeneity in vegetation and moisture conditions across spatial scales. Overall, we find a signal of local paleoenvironmental stability during the MCO; however, a significant drying trend in the Crowder Formation does correspond with faunal turnover and reduction in the number of taxa present. High species diversity within faunal assemblages, especially among small mammals, and fewer shared species between the Crowder and Cajon Valley assemblages than expected based on bootstrap analysis indicate that peak mammal diversity was accommodated at both local and regional scales during sustained tectonic activity and the MCO in western North America.

Craniodental morphology and diet ofLeptarctus oregonensis(Mammalia, Carnivora, Mustelidae) from the Mascall Formation (Miocene) of central Oregon

AbstractThe Leptarctinae are an enigmatic subfamily of mustelids present in North America and Eurasia during the Miocene (Arikareean to Hemphillian North American Land Mammal Ages). Their diet and ecology have been particularly controversial. Some workers have suggested they were similar to koalas, whereas others suggested they were crushing omnivores analogous to raccoons.Leptarctus oregonensisStock, 1930, a poorly known leptarctine from the early Barstovian, is represented by fragmented cranial elements and isolated teeth from the Mascall Formation of Oregon, and some fairly complete but undescribed material from the Olcott Formation of western Nebraska. Herein, we describe the first well-preserved skull ofL.oregonensisfrom the type formation. Based on this new specimen, we confirm thatL.oregonensisis a distinct species fromL.primusLeidy, 1856 andL.ancipidensWhite, 1941 that is characterized by a distinct morphology of its tympanic projections and first upper molars. We are also able to describe intraspecific variation withinL.oregonensiscoinciding with the geographic distribution of the specimens (Oregon and Nebraska). The most variable characters are concentrated in the morphology of the frontals and the upper fourth premolar. Additional specimens will be needed to settle the debate over sexual dimorphism in this species, but this new specimen suggests thatLeptarctus oregonensis, despite being one of the smallest members of the Leptarctinae, was an animal-dominated omnivore with considerable crushing ability.

Morphological variation, phylogenetic relationships, and geographic distribution of the Baenidae (Testudines), based on new specimens from the Uinta Formation (Uinta Basin), Utah (USA).

We described newly discovered baenid specimens from the Uintan North American Land Mammal Age (NALMA), in the Uinta Formation, Uinta Basin, Utah. These specimens include a partial skull and several previously undescribed postcranial elements of Baena arenosa, and numerous well-preserved shells of B. arenosa and Chisternon undatum. Baenids from the Uintan NALMA (46.5–40 Ma) are critical in that they provide valuable insight into the morphology and evolution of the diverse and speciose baenid family near the end of its extensive radiation, just prior to the disappearance of this clade from the fossil record. These Uintan specimens greatly increase the known variation in these late-surviving taxa and indicate that several characters thought to define these species should be reassessed. The partial cranium of B. arenosa, including portions of the basicranium, neurocranium, face, and lower jaw, was recently recovered from Uinta B sediments. While its morphology is consistent with known specimens of B. arenosa, we observed several distinct differences: a crescent-shaped condylus occipitalis that is concave dorsally, tuberculum basioccipitale that flare out laterally, and a distinct frontal-nasal suture. The current sample of plastral and carapacial morphology considerably expands the documented variation in the hypodigms of B. arenosa and C. undatum. Novel shell characters observed include sigmoidal extragular-humeral sulci, and small, subtriangular gular scutes. Subadult specimens reveal ontogenetic processes in both taxa, and demonstrate that diagnostic morphological differences between them were present from an early developmental age.

Paleontology and stratigraphy of Middle Eocene rock units in the southern Green River and Uinta Basins, Wyoming and Utah

The Bridger Formation is restricted to the Green River Basin in southwest Wyoming, and the Uinta and Duchesne River Formations are located in the Uinta Basin in Utah. These three rock units and their diverse fossil assemblages are of great scientific importance and historic interest to vertebrate paleontologists. Notably, they are also the stratotypes from oldest to youngest for the three middle Eocene North American Land Mammal Ages—the Bridgerian, Uintan, and Duchesnean. The fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning approximately 10 million years (49 to 39 Ma). This article provides a detailed field excursion through portions of the Green River and Uinta Basins that focuses on locations of geologic, paleontologic, and historical interest. In support of the field excursion, we also provide a review of current knowledge of these formations with emphasis on lithostratigraphy, biochronology, depositional, and paleoenvironmental history, and the history of scientific exploration.

FACIES, ENVIRONMENTS, AND FOSSIL PRESERVATION IN THE BARSTOW FORMATION, MOJAVE DESERT, CALIFORNIA

Continental deposits of the middle Miocene Barstow Formation formed in an extensional basin of the Mojave region. Mammalian faunas of the type section in the Mud Hills, California, are the basis for defining the Barstovian North American Land Mammal Age. Prior mapping, lithostratigraphy, geochronology, and fossil collecting have established a structural, chronostratigraphic, and biostratigraphic framework for the Barstow Formation. Here, we analyze the sedimentary facies of the lithostratigraphic sequence, infer the major depositional environments, and assess controls on fossil preservation in relation to major facies. We recognize six major facies associations that represent alluvial fans, shallow or seasonal lakes, and channels and floodplains. The transition from older, fan-dominated to younger, floodplain-dominated environments reflects changes in tectonics, accommodation, drainage, and depositional settings during the formation and filling of the basin. Fossil-mammal concentrations are common in four facies associations. Body fossils are abundant in two facies associations that represent well-drained floodplains and spring-fed wetlands. Fossil concentrations are moderately abundant in facies associations that represent floodplains and channel deposits, and fossils are rare in facies associations that represent alluvial fans and lake margins. The highest frequency of fossil localities occurs in the facies associations representing both suitable life habitats and high preservation potential for terrestrial mammals.

New Material of Eocene Helaletidae (Perissodactyla, Tapiroidea) from the Irdin Manha Formation of the Erlian Basin, Inner Mongolia, China and Comments on Related Localities of the Huheboerhe Area

ABSTRACT Perissodactyls first appeared at the beginning of the early Eocene and reached their highest diversity, dominating contemporaneous mammalian faunas in species richness during the middle Eocene. Tapiroidea is an important perissodactyl group that includes earliest-Eocene forms, such as Orientolophus as well as extant taxa (such as Tapirus), that preserves numerous plesiomorphic characters. Because tapiroids were widely distributed in North America and Asia in the middle Eocene, they have played an important role in biostratigraphically defining middle Eocene North American Land Mammal Ages (NALMA) and Asian Land Mammal Ages (ALMA), respectively, as well as in biostratigraphic correlation between the two continents. Here we report a new cranial specimen of middle Eocene helaletid Paracolodon fissus and a maxilla of Desmatotherium mongoliense from the middle Eocene Irdin Manha Formation of the Erlian Basin, Inner Mongolia, China. Paracolodon fissus was previously assigned to Desmatotherium, Helalete...

<em>Procerberus</em> (Cimolestidae, Mammalia) from the Latest Cretaceous and Earliest Paleocene of the Northern Western Interior, USA

Three species of the cimolestid Procerberus are currently recognized in the northern North American Western Interior in latest Cretaceous and earliest Paleocene (Puercan North American Land Mammal Age) faunas: P. formicarum, P. andesiticus, and P. grandis. Analysis of a new topotypic sample of P. formicarum from the Bug Creek Anthills locality provides an estimate of the range of variation of its postcanine dentition. The three currently recognized species occur in Puercan 1 (Pu1) interval zone faunas, but two other occurrences indicate that the genus originated and initially diversified prior to the Cretaceous/Paleogene boundary. Rare occurrences at several localities and entries in faunal lists suggest even greater taxonomic diversity. Limited evidence suggests continued diversification in the later Puercan and possible survival of the genus into the Torrejonian. Procerberus grandis or a closely related species may be a sister group of primitive taeniodonts.

New late Paleocene (late middle Tiffanian) mammals from the Roche Percée local fauna, south-eastern Saskatchewan, Canada

An exceptionally large and diverse assemblage of mammals from the early late Paleocene (about 58 million years ago) has been collected from the Ravenscrag Formation near Roche Percée, south-eastern Saskatchewan, Canada. Previous research of the Roche Percée local fauna has examined only a small portion of the mammals, with the vast majority of taxa remaining unstudied. Identification and descriptions of these latter taxa are provided here. With these new additions, the assemblage is now known to include 44 mammalian species. Notable among these findings is the substantial collection of the erinaceomorph lipotyphlan Litocherus lacunatus, the remarkable diversity of viverravid carnivorans, and the recovery of some of the first known elements of the upper dentition of the pantolestid Besseocetor pilodontus. A complete description of the mammalian fauna supports previous assignments of a late middle Tiffanian North American Land Mammal Age (Ti4 lineage zone) to the Roche Percée local fauna. Faunal comparisons further suggest a close similarity of the Roche Percée assemblage to the near contemporaneous Divide Quarry local fauna from the Bighorn Basin, northern Wyoming, but also reveal some similarities to slightly older middle Tiffanian local faunas (Ti3 lineage zone) at localities in the Paskapoo Formation of central Alberta. The specimens from the Roche Percée local fauna represent the largest and most taxonomically diverse assemblage of late middle Tiffanian mammals yet known, offering a unique perspective on mammalian evolution and diversity in North America during this time interval.

Paleontology and stratigraphy of Middle Eocene rock units in the southern Green River and Uinta Basins, Wyoming and Utah

The Bridger Formation is restricted to the Green River Basin in southwest Wyoming, and the Uinta and Duchesne River Formations are located in the Uinta Basin in Utah. These three rock units and their diverse fossil assemblages are of great scientific importance and historic interest to vertebrate paleontologists. Notably, they are also the stratotypes from oldest to youngest for the three middle Eocene North American Land Mammal Ages—the Bridgerian, Uintan, and Duchesnean. The fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning approximately 10 million years (49 to 39 Ma). This article provides a detailed field excursion through portions of the Green River and Uinta Basins that focuses on locations of geologic, paleontologic, and historical interest. In support of the field excursion, we also provide a review of current knowledge of these formations with emphasis on lithostratigraphy, biochronology, depositional, and paleoenvironmental history, and the history of scientific exploration.

Integrated Chronology, Flora and Faunas, and Paleoecology of the Alajuela Formation, Late Miocene of Panama.

The late Miocene was an important time to understand the geological, climatic, and biotic evolution of the ancient New World tropics and the context for the Great American Biotic Interchange (GABI). Despite this importance, upper Miocene deposits containing diverse faunas and floras and their associated geological context are rare in Central America. We present an integrated study of the geological and paleontological context and age of a new locality from Lago Alajuela in northern Panama (Caribbean side) containing late Miocene marine and terrestrial fossils (plants, invertebrates, and vertebrates) from the Alajuela Formation. These taxa indicate predominantly estuarine and shallow marine paleoenvironments, along with terrestrial influences based on the occurrence of land mammals. Sr-isotope ratio analyses of in situ scallop shells indicate an age for the Alajuela Formation of 9.77 ± 0.22 Ma, which also equates to a latest Clarendonian (Cl3) North American Land Mammal Age. Along with the roughly contemporaneous late Miocene Gatun and Lago Bayano faunas in Panama, we now have the opportunity to reconstruct the dynamics of the Central America seaway that existed before final closure coincident with formation of the Isthmus of Panama.

A pantodont (Mammalia) from the latest Puercan North American Land Mammal Age (earliest Paleocene) of the Western Interior, USA

Discovery of an Alcidedorbignya-like isolated upper molar in an early Paleocene (latest Puercan, Puercan 3, North American Land Mammal Age) local fauna found in the Tullock Member of the Fort Union Formation in northeastern Montana has been cited in the paleontological literature. This fossil is described, and a new genus and species, Crustulus fontanus, are established. They add to the taxonomic diversity of Puercan 3 local faunas in the North America Western Interior. The tooth’s morphology including a deep ectoflexus, nearly parallel preparacrista and postmetacrista, and expansion of the postcingulum, suggests evolution to accommodate increased herbivory. The appearance of C. fontanus with no clearly related taxa in older Puercan or Lancian (latest Cretaceous) local faunas of the currently sampled areas of the Western Interior indicates it probably was yet another post-Cretaceous/Paleogene boundary immigrant into this region. The few characters preserved in the single upper molar strongly suggest but do not conclusively indicate phylogenetic affinities with pantodonts. Perhaps C. fontanus was a member of yet another lineage stemming from the common ancestry of pantodonts and tillodonts. It is the oldest record of this complex group in North America.http://www.zoobank.org/urn:lsid:zoobank.org:act:3643EA78-9A1A-4A2A-BFAF-4C2B6355B834

Late Oligocene-Early Miocene magnetochronology of the mammalian faunas in the Lanzhou Basin-environmental changes in the NE margin of the Tibetan Plateau.

A large number of terrestrial mammalian fossils were reported in the well-exposed Paleogene and Neogene fluvio-lacustrine strata in Western China. Their accurate ages are crucial to understand the mammalian and environmental evolution associated with the step-wise uplift of the Tibetan Plateau. At present their ages are surprisingly poorly constrained. Here, we present a high-resolution magnetostratigraphic dating of the Late Oligocene–Early Miocene mammal assemblages from a 233-m thick fluvio-lacustrine section in the Lanzhou Basin located at the northeastern margin of the Tibetan Plateau, China. The results suggest that the section spans from the polarity subchron C6Cn.2r to C5En, i.e. ranging from ca 23 to 18 Ma. This magnetochronology provides considerably more robust ages for three associated land mammalian faunal assemblages. Updated ages end the debate on existing ambiguous and distinctly different magnetostratigraphic correlations for those Late Oligocene–Early Miocene assemblages. The new ages now enable precise correlation of these faunas to the European Land Mammal and North American Land Mammal Ages. The faunal assemblages further suggest a mixed setting of woodlands and grasslands associated with a humid environment in the Lanzhou Basin during the Late Oligocene–Early Miocene, in contrast to its modern poor vegetation cover and arid environment.

A small-bodied species of Brontotheriidae from the middle Eocene Nut Beds of the Clarno Formation, John Day Basin, Oregon

AbstractWe diagnose a new species of Brontotheriidae from a middle Eocene locality, the Clarno Nut Beds, from the Clarno Formation, John Day Basin, Central Oregon. Though renowned for its richness in fossil flora, fossil vertebrates are rare in the Clarno Nut Beds and this new species is the most abundantly represented mammal. Radiometric dating constrains the age of the Nut Beds fauna to about 43.76 Ma within the Uintan North American Land Mammal Age. This new taxon, represented by numerous cranial, mandibular, and dental specimens, is comparatively small for a brontothere and notable for its cranio-caudally shorted nasal incision, a trait shared with three larger-bodied middle Eocene species,Metatelmatherium ultimum,Wickia brevirhinus, andSthenodectes incisivum. Phylogenetic analysis suggests the sister taxon of the Nut Beds brontothere could be one of two species—Wickia brevirhinusfrom the Sand Wash Basin of Colorado and Washakie Formation of Wyoming, orMetatelmatherium ultimum, a pan-Beringian species known from the Uintan Formation of Utah (and other Uintan age deposits) and the “Irdin Manha” Formation of Inner Mongolia, China. Phylogenetic results also indicate that the Nut Beds brontothere is a dwarf taxon. Though brontotheres are renowned for having evolved very large body sizes, this new brontothere is one of several discovered in recent decades that suggest evolutionary reductions in body size may have been relatively common in Brontotheriidae.

LA-ICP-MS Zircon U—Pb Dating of Acidic Tuff from the Eocene Akasaki Formation, Amakusa, Kumamoto Prefecture, Western Kyushu, Japan: Implications for the Age of the Land Mammal Fauna in Japan

Abstract. We obtained zircon U—Pb ages using LA-ICP-MS for an acidic tuff bed in the upper part of the Akasaki Formation, a basal unit of the Eocene sequence in the Amakusa area, Kumamoto Prefecture, Japan. The U—Pb age of 49.1±0.4 Ma (95% confidence interval) suggests a late early Eocene age. Our result is important for biochronological assessment of the land mammal fauna of the Akasaki Formation. The new age date supports the correlation of the Akasaki mammal fauna with the Bridgerian North American Land Mammal Age.

Skeletal Anatomy of the North American Pangolin Patriomanis americana (Mammalia, Pholidota) from the Latest Eocene of Wyoming (USA)

Patriomanis americana is the only pangolin (Mammalia, Pholidota), living or extinct, known from the Western Hemisphere. It derives from latest Eocene (Chadronian North American Land Mammal Age) deposits from central Wyoming and western Montana. Since its initial description more than 40 years ago based on a partial skeleton, several nearly complete skeletons have been discovered, together including nearly every bone in the skeleton. This taxon is thus not only the most completely preserved fossil pangolin but is also among the best preserved of any Eocene mammal taxon. In the present study we have prepared a detailed, bone-by-bone description of the osteology of Patriomanis, comparing it with other well-known fossil pangolin skeletons (Eomanis, Euromanis, Cryptomanis, and Necromanis), as well as representatives of the three extant pangolins genera (Manis, Smutsia, Phataginus). We provide a catalog of all known Patriomanis specimens and their provenance and an extensive series of measurement tables incorporating the comparative taxa. We analyze the alpha-level taxonomy of the genus, concluding that all specimens should be kept in a single species, Patriomanis americana, based on currently available fossil material. We summarize the taxonomic and phylogenetic position of Patriomanis and discuss its implications for the biogeographic history of the order Pholidota. We analyze the paleobiology of Patriomanis, concluding that it was likely a myrmecophagous, arboreal animal with a prehensile tail. Last, we discuss its paleoecology, suggesting that its late appearance in the Eocene record, during a time of global cooling, may imply that earlier pangolins are waiting to be discovered in the Eocene record of Asia and North America.

Climate and landscape reconstruction of the Arroyo Chijuillita Member of the Nacimiento Formation, San Juan Basin, New Mexico: Providing environmental context to early Paleocene mammal evolution

The sedimentologic, stratigraphic, and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower Paleocene Arroyo Chijuillita Member of the Nacimiento Formation located in the Bisti/De-Na-Zin Wilderness Area was examined to provide paleoenvironmental context for the Puercan North American Land Mammal Age (NALMA) terrestrial ecosystems of the San Juan Basin, New Mexico. The studied outcrop spans the middle and late Puercan (Pu2-Pu3) NALMA, and thus is an ideal location to assess the potential causes of faunal turnover between Pu2 and Pu3. The stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine-grained floodplain deposits, including paleosols that document variability in drainage and maturity. Quantitative and qualitative reconstructions of paleoclimate from paleosols, supplemented by analyses of fossil floras, indicate no change in climate through the studied interval. Further, there is no evidence that regional tectonics relate to changes in depositional environments. Given the lack of evidence for climate change or regional tectonics, and the characteristics of the fluvial facies and the paleosols across the study locality, we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration. Additionally, the stable climatic conditions and lack of tectonic influence between the Pu2 and Pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes (i.e. climate or tectonics) and is instead probably the result of rapid evolution following the K-Pg boundary and/or competition from the migration of new mammalian species into the basin.

A new late Hemingfordian vertebrate fauna from Hawk Rim, Oregon, with implications for biostratigraphy and geochronology

ABSTRACTThe Hemingfordian North American Land Mammal Age is not well sampled, especially in the Pacific Northwest. Here we present both a description of a new fauna and two radiometric dates, 16.26 Ma and 16.44 Ma, constraining the Hawk Rim locality of central Oregon. Hawk Rim represents the first diverse late Hemingfordian fauna in the Northwest and is one of the stratigraphically lowest fossiliferous outcrops of the Mascall Formation. Much of Oregon was blanketed by Columbia River Flood Basalts during late Hemingfordian time, limiting not only outcrops but places for organisms to have survived. The site yields a taxonomically rich fauna sharing strong faunal similarity with the type locality of the Mascall but also containing taxa new to the formation and region. We describe occurrences of five genera of Artiodactyla, four genera of Perissodactyla, three genera of Rodentia, and six genera of Carnivora, with all but three new occurrences for the Hemingfordian of the Pacific Northwest. In particular, the carnivore fauna extends the geographic and temporal range of several carnivorans, and we describe a new hypercarnivorous mustelid, Watay tabutsigwii.http://zoobank.org/urn:lsid:zoobank.org:pub:B415069F-8BE6-4629-A872-5A640A644210SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: McLaughlin, W. N. F., S. S. B. Hopkins, and M. D. Schmitz. 2016. A new late Hemingfordian vertebrate fauna from Hawk Rim, Oregon, with implications for biostratigraphy and geochronology. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1201095.

First occurrence of <i>Panthera atrox</i> (Felidae, Pantherinae) in the Mexican state of Hidalgo and a review of the record of felids from the Pleistocene of Mexico

Abstract. Panthera atrox was a common large-sized cat in North America during the late Pleistocene. An isolated lower canine and a fifth metacarpal bone referable to this species were recovered from fluvial Quaternary deposits that outcrop in southeastern Hidalgo, central Mexico. Associated fossil material belonging to Bison indicates a Rancholabrean North American Land Mammal Age; the age assignment is corroborated by the presence of P. atrox. A comparative study with selected specimens of Panthera and Smilodon indicates that the Hidalgoan sample shares the following diagnostic features with P. atrox: a large, robust, and non-strongly curved lower canine; a large and relatively slender fifth metacarpal with a well-developed projection on the palmar side at the proximal end, narrow articulating surface for the unciform; a narrow notch on the articulating surface for the fourth metacarpal; and a diaphysis that at the middle is oval in cross section. The record supplements the evidence of P. atrox in central Mexico and represents the first reported occurrence of this cat species in the state of Hidalgo. By the same token, the known geographic distribution of P. atrox in the Mexican territory suggests that it was relatively common in temperate areas of central Mexico between 19 and 24° N at an altitudinal range from 1500 to 2250 m a.s.l. The large size (mean body mass of 300 kg) and hypercarnivorous adaptations of the American lion suggest it was the top predator of the mammalian community recorded at southeastern Hidalgo, displacing other members of the carnivore guild at the mesopredator level, such as the dire wolf (Canis dirus ), which has been also reported in the area. The high diversity of large herbivores recorded at southeastern Hidalgo, which in turn could represent potential prey of P. atrox, suggests that some areas that now are part of central Mexico were suitable hunting sites for this large-sized cat. A review of the Pleistocene record of Felidae from Mexico revealed that it encompasses 87.5 and 73.3 % of generic and specific diversity known for North America, respectively, including seven genera (Felis, Miracinonyx, Panthera, Puma, Lynx, Leopardus, and Smilodon) and 11 species (Felis rexroadensis, Miracinonyx inexpectatus, Panthera atrox, Panthera onca, Puma concolor, Puma yagouaroundi, Lynx rufus, Leopardus pardalis, Leopardus wiedii, Smilodon fatalis, and Smilodon gracilis). The majority of these taxa have been reported from numerous late Pleistocene localities; in particular, Panthera atrox was relatively common and widely distributed across the Mexican territory.

First records of Canis dirus and Smilodon fatalis from the late Pleistocene Tule Springs local fauna, upper Las Vegas Wash, Nevada.

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 of Camelopsand Mammuthus, and also includes relatively common remains of extinct Equusand Bisonas well as abundant vertebrate microfaunal fossils. Large carnivorans are rare, with only Puma concolor and Panthera atrox documented previously. Postcranial remains assigned to the species Canis dirus (dire wolf) and Smilodon fatalis (sabre-toothed cat) represent the first confirmed records of these species from the TSLF, as well as the first documentation of Canis dirus in Nevada and the only known occurrence of Smilodonin southern Nevada. The size of the recovered canid fossil precludes assignment to other Pleistocene species of Canis. The morphology of the felid elements differentiates them from other large predators such as Panthera, Homotherium, and Xenosmilus, and the size of the fossils prevents assignment to other species of Smilodon. The confirmed presence of S. fatalis in the TSLF is of particular interest, indicating that this species inhabited open habitats. In turn, this suggests that the presumed preference of S. fatalis for closed-habitat environments hunting requires further elucidation.

Lontra weiri, sp. nov., a Pliocene river otter (Mammalia, Carnivora, Mustelidae, Lutrinae) from the Hagerman Fossil Beds (Hagerman Fossil Beds National Monument), Idaho, U.S.A.

ABSTRACTA new Pliocene river otter is described from the Hagerman Fossil Beds (Hagerman Fossil Beds National Monument), Idaho. Lontra weiri, sp. nov., exhibits notable lutrine traits that closely align it to Old World Lutra and New World Lontra, which are morphologically similar but diphyletic. It is further assigned to Lontra based on known otter biogeography and molecular phylogenetic data. The Hagerman Fossil Beds are characterized by a Blancan North American Land Mammal Age fauna, and radiometric dates for the otter-bearing deposits are inferred as >3.79 Ma, making this the first pre-Pleistocene occurrence of Lontra. Hagerman has a rich and diverse carnivoran fauna with at least five families and 17 species represented, including a much larger otter, Satherium piscinarium. This new otter increases carnivoran richness at Hagerman and provides insight into the evolution of New World river otters.Citation for this article: Prassack, K. A. 2016. Lontra weiri, sp. nov., a Pliocene river otter (Mammalia, Carnivora, Mustelidae, Lutrinae) from the Hagerman Fossil Beds (Hagerman Fossil Beds National Monument), Idaho, U.S.A.. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1149075.http://zoobank.org/urn:lsid:zoobank.org:pub:94DDDDEB-FA6F-4CECBC65-81708EB74B9E