A Re-Evaluation of the Pleistocene Hellbender,Cryptobranchus guildayi

AimI re‐evaluate the specific biogeographical significance of each of the land bridges (Beringia, Thulean and De Geer) in the Northern Hemisphere during the latest Cretaceous–early Cenozoic, showing that the Thulean and De Geer routes did not operate contemporaneously.LocationNorthern Hemisphere landmasses.MethodsI review the recent climatic, sea‐level, geotectonic, palaeofloristic, and marine and terrestrial faunal data that have emerged since the establishment in the 1980s of the biogeographical concepts of the early Cenozoic Northern Hemisphere land bridges and present a synthesis supporting a revised scenario for early Cenozoic biogeographical development.ResultsPalaeogeographical and geotectonic data, supported by strong floral and faunal evidence, suggest that the palaeogeographical and chronological frames for the formation of all three land bridges are different from those originally proposed. Dispersal events via the causeways seem to have taken place during specific time intervals resulting from fluctuations in sea level and climate.Main conclusionsThe De Geer and Thulean routes were not contemporaneous. The former existed during the latest Cretaceous to the early Palaeocene, joining North America with Eurasia. The Thulean route became established well after the interruption of the De Geer route, offering a southerly connection between western Europe and North America in at least two episodes:c. 57 Ma andc. 56 Ma. The Bering route functioned in two warm periods: 65.5 Ma (coinciding with the De Geer route) andc. 58 Ma, during the Palaeocene (possible Eocene exposures are not considered here). The formation of the De Geer route explains faunal similarities between the Puercan and Torrejonian North American land mammal ages (NALMAs) and the Shanghuan Asian land mammal age (ALMA). The Thulean route explains faunal similarities between the Clarkforkian (Cf1) and Wasatchian (Wa0, 1)NALMAs, and the Cernaysian and Neustrian (PEI,II) European land mammal ages. The Bering route explains faunal similarities between the GashatanALMAand the Tiffanian (Ti5)NALMA.

Fossil vertebrates from the Alturas Formation in northern California have previously been considered important for defining the age of the boundary between the Hemphillian and Blancan North American Land Mammal Ages. Diatomaceous mudstone of the upper Alturas Formation contain fossil mammals including the arvicoline rodent Mimomys (Ogmodontomys) sawrockensis that is diagnostic of Blancan faunas. New paleomagnetic and geochemical data from the upper Alturas Formation constrain the age of the first stratigraphic occurrence of M. (O.) sawrockensis at Crowder Flat Road to between 4.5 and 4.6 Ma. This age is approximately 0.2-0.4 Ma younger than previously reported such that the oldest record of Mimomys in North America, south of 55oN, is from Panaca, Nevada, and is constrained geochronologically to be approximately 4.9 Ma. The Hemphillian – Blancan North American Land Mammal Age boundary probably occurs within magnetic polarity Chron C3n.3r at approximately 4.9 Ma.

Human impacts have left and are leaving distinctive imprints in the geological record. Here we show that in North America, the human-caused changes evident in the mammalian fossil record since c. 14,000 years ago are as pronounced as earlier faunal changes that subdivide Cenozoic epochs into the North American Land Mammal Ages (NALMAs). Accordingly, we define two new North American Land Mammal Ages, the Santarosean and the Saintagustinean, which subdivide Holocene time and complete a biochronologic system that has proven extremely useful in dating terrestrial deposits and in revealing major features of faunal change through the past 66 million years. The new NALMAs highlight human-induced changes to the Earth system, and inform the debate on whether or not defining an Anthropocene epoch is justified, and if so, when it began.

Megafauna: giant beasts of Pleistocene South America

Early Miocene land mammals from eastern North America are exceedingly rare. Over the past several decades a small, but significant, vertebrate fauna has been recovered by paleontologists and citizen scientists from the Belgrade Formation at the Martin Marietta Belgrade Quarry in eastern North Carolina. This assemblage has 12 land mammal taxa, including beaver (Castoridae), stem lagomorph, carnivorans (Mustelidae, Ailuridae), horses (Equidae), rhinoceros (Rhinocerotidae), tapir (Tapiridae), peccary (Tayassuidae), anthracothere (Anthracotheriidae), entelodont (Entelodontidae), and protoceratid (Protoceratidae). Taken together, the biochronology of this Maysville Local Fauna indicates a late Arikareean (Ar3/Ar4) to early Hemingfordian (He1) North American Land Mammal Age (NALMA). This interval, which includes the Runningwater Chronofauna, documents numerous important Holarctic immigrants, including Amphictis, Craterogale, and cf. Menoceras found at this locality. Strontium isotope stratigraphy (SIS) of shark teeth collected in situ from the Belgrade Formation yield an age of 21.4 ± 0.13 Ma, which validates the age of interbedded land mammals within this unit. It also is consistent with the late Arikareean (Ar3/Ar4) biochronology and Aquitanian Neogene marine stage. New SIS analyses of oysters (Striostrea gigantissima) and clams (Chione) from this mine, previously assigned to late Oligocene or Late Miocene, are significantly older (28.0 ± 0.22 Ma and 27.6 ± 0.26 Ma, respectively) than the land mammals. Depending upon stratigraphic interpretations, these may confirm an older marine facies within the Belgrade Formation. This locality is important because of its marine and terrestrial tie-ins that facilitate intercalibration of both NALMAs and Cenozoic marine stages.

The first postcranial oreodont (mammalia, Artiodactyla, Merycoidodontidae) skeleton from Mexico: Description and paleobiological significance

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.

We present new fossil records of the geoemydid turtle Bridgeremys pusilla from the Uinta Formation of Utah. Turtles are abundant throughout the unit, and known taxa are similar to those from the older strata in the Upper Green River Basin in Wyoming from the Bridger and Washakie Formations. B. pusilla is known from Bridgerian deposits but was not previously known from after the Turtle Bluff Member of the Bridger Formation. The taxon was coveal with two species of the geoemydid Echmatemys (E. callopyge and E. wyomingensis), a common genus of extinct pond turtles known primarily from lacustrine and fluvial deposits in western North America, including the Uinta Basin. In addition to previously documented morphological differences, our geometric morphometric analyses revealed significant differences in epiplastral morphology between B. pusilla and the two coeval Echmatemys species. Bridgeremys pusilla shared several morphological characters with Testudinidae. However, our anatomical network analysis suggests that the carapace of B. pusilla distributed stress forces in a manner more similar to emydids (basal and derived) than to derived testudinoids (Testudinidae and Emydidae), including Echmatemys species. This finding changes our understanding of the ecology of the species and sheds light onto how geoemydid turtles of the Uinta Formation may have partitioned the available ecospace. These new Uintan records extend the geographic range of B. pusilla into the Uinta Basin and stratigraphically through the top of the Uinta Formation, extending the temporal range of the taxon by more than 4 million years through the Uintan North American Land Mammal Age to the base of the Duchesne River Formation.

New specimens of the mesonychid Dissacus praenuntius from the early Eocene of Wyoming and evaluation of body size through the PETM in North America

Although the Arikareean North American land mammal age was first typified in the Great Plains, the succession there contains significant unconformities, a generally poor magnetic record, relatively sparse radioisotopic calibration, and a major faunal hiatus. In the John Day Valley of central Oregon, however, is a thick, remarkably complete sequence of Oligocene through early Miocene strata (the John Day Formation) potentially amenable to addressing these shortcomings and long known to harbor one of the richest records of mid‐Tertiary mammals in North America. Since Prothero and Rensberger’s first magnetostratigraphic study of the John Day Formation in 1985, new advances in geochronology, together with a more comprehensive suite of paleomagnetic sections keyed to new radioisotopic and biostratigraphic data, have greatly enhanced chronostratigraphic precision. In our attempt to refine John Day chronostratigraphy, we sampled nearly 300 sites for magnetostratigraphy over a 500‐m‐thick interval and used several radioisotopically dated volcanic tuffs for our correlation with the geomagnetic polarity timescale. Many of the rocks analyzed showed unusual magnetic behavior, possibly due to the known zeolitization in this region, thereby precluding an abundance of class 1 polarity determinations. Nevertheless, preliminary results indicate that the Turtle Cove Member stratigraphically upward through the lower Kimberly Member extends from late chron C12n through C7n.1r, or from about 30.6 to 24.1 Ma. Intensive radioisotopic and magnetostratigraphic characterization of these strata provides a framework by which the associated biostratigraphy is assessed for biochronological significance relative to fossiliferous successions of the Great Plains, in turn resulting in reassessment of Arikareean subbiochron (Ar1–Ar4) boundaries. We present a revision of those boundaries that differs from their traditional timing as a hypothesis for testing in other locations.

Recent studies of early Paleocene stratigraphic sections across the U.S. Western Interior are refining our understanding of the biotic recovery in the aftermath of the Cretaceous–Paleogene (K–Pg) mass extinction event. Herein we present magnetostratigraphic data from an approximately 600-m-thick section of strata of the Ferris Formation in the Hanna Basin, south-central Wyoming, that spans the K–Pg boundary and includes in conformable superposition the three subdivisions of the earliest Paleocene Puercan North American Land Mammal Age: interval zones Pu1, Pu2, and Pu3. Prior studies on early Paleocene stratigraphic sections in Montana to the north of Hanna Basin and in Colorado and New Mexico to the south have been only marginally successful in defining the temporal boundaries of these divisions. This earlier work typically restricted Pu1 entirely within reversed magnetochron C29r, Pu2 entirely within normal magnetochron C29n, and at least the early part of Pu3 in C29n, as well. Results of the present study confirm what has been only tentatively suggested previously: that interval zone Pu2 begins in the youngest part of C29r, with later Pu2 fauna extending into C29n. Although Pu3 is known to begin in C29n, its younger limit remains unknown in our Hanna Basin section, because the top of the local Puercan is well above the stratigraphic level of our sampling for this project. We estimate a date for the Pu1–Pu2 boundary in the Hanna Basin section of approximately 65.82 Ma—nearly 70 k.y. earlier than prior estimates. This boundary marks the transition from the Pu1 survival fauna to later phases of the mammalian recovery characterized by a significant increase in diversity, appearance of considerably larger-bodied mammals, and greater dental and dietary specializations.

North American glyptodonts originated from South American ancestors during the Great American Biotic Interchange no later than early Blancan North American Land Mammal Age (NALMA). A substantial expansion in population samples from the late Blancan 111 Ranch fauna of southeastern Arizona, several late Blancan faunas in New Mexico, and the early Blancan–Irvingtonian faunas of Guanajuato, Mexico, permit, analysis of sexual dimorphism and ontogeny of Glyptotherium texanum Osborn, 1903. Growth of carapacial osteoderms was allometric, including changes of the external sculpturing. Overall anatomy of the carapace changed with growth, with development of distinctive pre-iliac and post-iliac regions in lateral profile of adults. Skulls of adults possess a unique boss on the anterior surface of the descending process of the zygomatic arch that is not present in juveniles. Sexual dimorphism involves differences in anatomy of lateral and posterior osteoderms. Glyptotherium arizonae Gidley, 1926, is a junior synonym of G. texanum. The temporal distribution of G. texanum extends from early Blancan NALMA to Irvingtonian NALMA, with geographical distribution from Central America and Mexico to southern United States.

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 Clarkforkian (latest Paleocene) North American Land Mammal Age (NALMA) remains a relatively poorly sampled biostratigraphic interval at the close of the Paleocene epoch that is best known from the Bighorn Basin of northwestern Wyoming. A period of global warming between the cooler early and middle Paleocene and the extreme warming of the early Eocene, the Clarkforkian witnessed significant floral and faunal turnover with important ramifications for the development of Cenozoic biotas. The combination of warming global climates with mammalian turnover (including likely intercontinental dispersals) marks the Clarkforkian and the succeeding Wasatchian (Earliest Eocene) NALMAs as periods of intense interest to paleobiologists and other earth scientists concerned with aspects of biostratigraphy and with the biotic effects of climate change in the past. In this paper we describe a new Clarkforkian mammalian fauna from the Great Divide Basin of southwestern Wyoming with some surprising faunal elements that differ from the typical suite of taxic associations found in Clarkforkian assemblages of the Bighorn Basin. Several different scenarios are explored to explain this “anachronistic” assemblage of mammals from southern Wyoming in relation to the typical patterns found in northern Wyoming, including the concepts of basin-margin faunas, latitudinal and climatic gradients, and a chronologically transitional fauna. We suggest that the observed faunal and biostratigraphic differences between southern and northern Wyoming faunas most likely result from latitudinal and associated climatic differences, with floral and faunal changes being reflected somewhat earlier in the south during this period of marked climate change.

The developmental history of North American Land Mammal Ages (NALMAs), their integration with radioisotopic and magnetic polarity dating systems, and relationships to stratigraphic codes and guides are briefly reviewed. Augmented by examples, the need for NALMAs to be supplied with detailed biostratigraphic information is stressed. NALMAs make powerful contributions to the discussion of geohistorical events at intra- and intercontinental scales.