Carboniferous tetrapod biostratigraphy, biochronology and evolutionary events

Tetrapod (amphibian and amniote) fossils of Carboniferous age are known almost exclusively from the southern part of a paleoequatorial Euramerican province. The stratigraphic distribution of Carboniferous tetrapod fossils is used to identify five land-vertebrate faunachrons: (1) Hortonbluffian (Givetian-early Visean), the time between the FAD of tetrapods to the beginning of the Doran; (2) Doran (late Visean-early Bashkirian), the time between the FAD of the baphetid Loxomma and the beginning of the Nyranyan; (3) Nyranyan (late Bashkirian-Moscovian), the time between the FAD of the eureptile Hylonomus and the beginning of the Cobrean; (4) Cobrean (Kasimovian-late Gzhelian), the time between the FAD of the eupelycosaur Ianthasaurus and the beginning of the Coyotean; and (5) Coyotean (late Gzhelian-early Permian), the time between the FAD of the eupelycosaur Sphenacodon and the beginning of the Seymouran. This biochronology provides insight into some important evolutionary events in Carboniferous tetrapod evolution.

Biostratigraphy of the Lystrosaurus declivis Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa

The earliest Triassic (Induan) Lystrosaurus Assemblage Zone has long been recognised as a particularly significant biozone in palaeoecological and palaeoenvironmental studies as it contains a community assemblage that records the survival and recovery from the end-Permian mass extinction (EPME). Here renamed the Lystrosaurus declivis Assemblage Zone it represents the best record globally of the ecological changes in terrestrial community structure and stability during this time period. The assemblage is dominated by two species of small to medium-sized herbivorous dicynodonts L. declivis and L. murrayi that co-occur in equal abundance, along with a range of smaller and less common faunivorous and insectivorous taxa. The latter comprise cynodonts (Thrinaxodon, Galesaurus, and Platycraniellus), therocephalians (Olivierosuchus, Regisaurus and Promoschorhynchus), the diminutive parareptiles (Saurodektes, Sauropareion, Colleta, Phonodus and Procolophon) and eureptilian arrivals possibly representing immigrant taxa (Prolacerta, Heleosuchus and Noteosuchus), among others. The attendant large carnivores were sabre-toothed Moschorhinus and the long-snouted archosauromorph Proterosuchus. In the aftermath of the mass extinction, new small temnospondyl taxa established their first occurrences i.e. Broomistega, Lydekkerina, and Micropholis, and have relatively high abundances compared to earlier temnospondyl records in the Karoo. Lithostratigraphically, the biozone for the most part spans the upper Palingkloof Member of the Balfour Formation and the overlying Katberg Formation in the western part of the basin, and the Normandien Formation in the east. The Lystrosaurus declivis Assemblage Zone of the main Karoo Basin hosts the type locality of the global Lootsbergian land-vertebrate faunachron. The biozone is one of the most widespread terrestrial faunal assemblages of western Gondwana with closely related species occurring in India and Antarctica. Similar, but much more distantly related taxa, occur in Induan-aged strata of Russia, China and Brazil.

Assesssing the role of humans in Greater Antillean land vertebrate extinctions: new insights from Cuba

ABSTRACTThe Caribbean archipelago is a hotspot of biodiversity characterized by a high rate of extinction. Recent studies have examined these losses, but the causes of the Antillean Late Quaternary vertebrate extinctions, and especially the role of humans, are still unclear. Current results provide support for climate-related and human-induced extinctions, but often downplaying other complex bio-ecological factors that are difficult to model or to detect from the fossil and archaeological record. Here, we discuss Caribbean vertebrate extinctions and the potential role of humans derived from new and existing fossil and archaeological data from Cuba. Our results indicate that losses of Cuba’s native fauna occurred in three waves: one during the late Pleistocene and early Holocene, a second during the middle Holocene, and a third one during the last 2 ka, coinciding with the arrival of agroceramists and the early Europeans. The coexistence of now-extinct species with multiple cultural groups in Cuba for over 4 ka implies that Cuban indigenous non-ceramic cultures exerted far fewer extinction pressures to native fauna than the later agroceramists and Europeans that followed. This suggests a determinant value to increased technological sophistication and demographics as the most plausible effective extinction drivers.

Late Holocene land vertebrate fauna from Cueva de los Nesofontes, Western Cuba: stratigraphy, last appearance dates, diversity and paleoecology

ABSTRACTHere we report a Late Holocene fossil-rich cave deposit from Cueva de los Nesofontes, Mayabeque Province, Cuba. The deposit’s formation and its fauna were studied through a multidisciplinary approach that included stable isotope analyses, radiocarbon chronology, stratigraphy, sedimentology, and taphonomy. Thousands of microvertebrate skeletal remains were recovered, representing a diverse land vertebrate fauna that included threatened and extinct species. The deposit is characterized by profuse Nesophontes remains due to raptor predation. Previously unreported last appearance dates are provided for the extinct island-shrew Nesophontes major, the bats Artibeus anthonyi and Phyllops vetus. Radiocarbon (14C AMS) age estimates between ∼1960 rcyr BP and the present were recovered. The presence of locally extinct species, including the endemic parakeet Psittacara eups, the flicker Colaptes cf. auratus/fernandinae, and the lipotyphlan Solenodon cubanus suggests that these species had broader distributions in the near past. Isotope analyses and faunal composition indicate the previous presence of diverse habitats, including palm grove savannas and mixed woodlands. Isotopes also provide insight into the habitat and coexistence of the extinct bat Artibeus anthonyi and extant A. jamaicensis, the diet of Nesophontes major, and local paleoenvironmental conditions. Oxygen isotopes reveal an excursion suggestive of drier/colder local conditions between 660 and 770 AD. Our research further expands the understanding of Cuban Quaternary extinction episodes and provides data on the distribution and paleoecology of extinct taxa. It supports the conclusion that many Cuban extinct species survived well into the pre-Columbian late Holocene and retained wide distribution ranges until human colonization.

First high-precision U–Pb CA–ID–TIMS age for the Battle Formation (Upper Cretaceous), Red Deer River valley, Alberta, Canada: implications for ages, correlations, and dinosaur biostratigraphy of the Scollard, Frenchman, and Hell Creek formations

The Battle Formation (BFm) is a widespread Upper Cretaceous marker horizon in western Canada that records a time of low sediment input and marks the boundary between the Edmontonian and Lancian land-vertebrate ages. Here, we present the first high-precision U–Pb CA–ID–TIMS age of 66.936 ± 0.047/0.060/0.140 Ma for the Battle bentonite, an altered vitric ash in the upper portion of the BFm at Knudsen’s Farm in the Red Deer River valley of Alberta. This age supersedes those previously reported, confirms that rates of sediment accumulation for the formation were very low (∼1.40 cm/ka), and allows us to interpolate an age range of ∼66.88–67.20 Ma for the BFm. Our data also provide a maximum age of ∼66.88 Ma for the base of the overlying Scollard Formation, a dinosaur-rich unit. We combine our age data with calibrated magneto- and palynostratigraphic data to assess chronostratigraphic correlations among the Scollard Formation of Alberta, the Frenchman Formation of Saskatchewan, and the Hell Creek Formation in eastern Montana. Whereas the combined data support previous interpretations that equate the age ranges of the Scollard Formation, Frenchman Formation, and the upper one third of the Hell Creek Formation in eastern Montana, they also indicate that all of the lower one third (L3) and part of the middle one third (M3) of the Hell Creek Formation in Montana are chronostratigraphically equivalent to all or part of the sub-BFm unconformity and the BFm in Alberta. Accordingly, a minimum age of ∼67.20 Ma is assessed for the base of the Hell Creek Formation in its type area.

Non-dinosaurian dinosauromorphs from the Chinle Formation (Upper Triassic) of the Eagle Basin, northern Colorado: Dromomeron romeri (Lagerpetidae) and a new taxon, Kwanasaurus williamparkeri (Silesauridae)

The “red siltstone” member of the Upper Triassic Chinle Formation in the Eagle Basin of Colorado contains a diverse assemblage of dinosauromorphs falling outside of Dinosauria. This assemblage is the northernmost known occurrence of non-dinosaurian dinosauromorphs in North America, and probably falls within the Revueltian land vertebrate estimated biochronozone (215–207 Ma, middle to late Norian). Lagerpetids are represented by proximal femora and a humerus referable to Dromomeron romeri. Silesaurids (non-dinosaurian dinosauriforms) are the most commonly recovered dinosauromorph elements, consisting of dentaries, maxillae, isolated teeth, humeri, illia, femora, and possibly a scapula and tibiae. These elements represent a new silesaurid, Kwanasaurus williamparkeri, gen. et sp. nov., which possesses several autapomorphies: a short, very robust maxilla with a broad ascending process, a massive ventromedial process, a complex articular surface for the lacrimal and jugal, and 12 teeth; 14 dentary teeth; an ilium with an elongate and blade-like preacetabular process and concave acetabular margin; a femur with an extremely thin medial distal condyle and a depression on the distal end anterior to the crista tibiofibularis. The recognition of K. williamparkeri further demonstrates the predominantly Late Triassic diversity and widespread geographic distribution across Pangea of the sister clade to Asilisaurus, here named Sulcimentisauria. Silesaurid dentition suggests a variety of dietary specializations from faunivory and omnivory in the Middle Triassic and early Late Triassic (Carnian), to herbivory in the Late Triassic (Carnian and Norian), with the latter specialization possibly coinciding with the radiation of Sulcimentisauria across Pangea. The extremely robust maxilla and folidont teeth of K. williamparkei may represent a strong herbivorous dietary specialization among silesaurids.