Rafael G. deÂ Souza, and Diogenes A. Campos (2018)Â
New Crocodyliform specimens from RecÃncavo-Tucano Basin (Early Cretaceous) of Bahia, Brazil.Â
Anais da Academia Brasileira de CiÃncias (advance online publication)
In 1940, L.I. Price and A. Oliveira recovered four crocodyliform specimens from the Early Cretaceous Bahia Supergroup (RecÃncavo-Tucano Basin). In the present work, we describe four different fossil specimens: an osteoderm, a fibula, a tibia, and some autopodial bones. No further identification besides Mesoeucrocodylia was made due to their fragmentary nature and the reduced number of recognized synapomorphies for more inclusive clades. With exception of the fibula, all other specimens have at least one particular feature, which with new specimens could represent new species. The new specimens described here increase the known diversity of Early Cretaceous crocodyliforms from Brazil. This work highlights the great fossiliferous potential of RecÃncavo-Tucano Basin with regard to crocodyliform remains.
Hao Lu, Da-Yong Jiang, Ryosuke Motani, Pei-Gang Ni, Zuo-Yu Sun, Andrea Tintori, Shi-Zhen Xiao, Min Zhou, Cheng Ji & Wan-Lu Fu (2018)
Middle Triassic Xingyi Fauna: showing turnover of marine reptiles from coastal to oceanic environments.
Palaeoworld 27(1): 107-116
The late Ladinian (Middle Triassic) Xingyi Fauna from the Zhuganpo Member of the Falang Formation yields abundant and well-preserved marine reptiles. Bed-by-bed excavation at Wusha in Xingyi of Guizhou Province reveals two marine vertebrate assemblages in a fossiliferous horizons that span 5.1 m in total thickness. The lower assemblage is marked by the near-shore sauropterygians, including the pachypleurosaur Keichousaurus, the nothosaurians Nothosaurus and Lariosaurus, with a strong paleobiogeographic affinity to western Tethys. The upper assemblage consists of oceanic ichthyosaurs and pistosaurs, including the large shastasaurid ichthyosaur Guizhouichthyosaurus, the euichthyosaur Qianichthyosaurus, pistosaurs Yunguisaurus and Wangosaurus, and the thalattosaur Xinpusaurus, with a closer paleobiogeographic affinity to North America. The coastal pachypleurosaur and nothosaurid sauropterygians disappeared in the upper assemblage, suggesting that they were replaced by an oceanic marine reptile community that emerged. The reptilian composition of the upper assemblage is similar to that of the Guanling Biota, which is of the Early Carnian (Late Triassic) in age and thus somewhat younger than the Xingyi Fauna. The ecological turnover of marine reptiles from near-shore to the open ocean community corresponds to the paleoenvironmental changes indicated by lithofacies analysis, Î13C and the global sea level changes.
Simon Scarpetta (2018)
The earliest known occurrence of Elgaria (Squamata: Anguidae) and a minimum age for crown Gerrhonotinae: Fossils from the Split Rock Formation, Wyoming, USA.Â
Palaeontologia Electronica 21.1.1FC 1-8
Gerrhonotinae is a clade of ecologically diverse anguid lizards with a relatively rich Cenozoic fossil record. The clade was well-studied by biologists researching molecular phylogenetics of extant lizards, but there is a paucity of reliable fossil data with which to analyze the diversification and historical biogeography of the group. Although several Cenozoic lizard fossils were attributed to Gerrhonotinae, most specimens were identified on the basis of overall morphological similarity to extant taxa. Here, I use an apomorphy-based approach to identify and describe the earliest known fossil referable to the extant gerrhonotine genus Elgaria and provide a minimum divergence time between stem Elgaria and other gerrhonotines. The fossil and associated fossil material were found in the Split Rock Formation in the Granite Mountains of central Wyoming. The minimum chronostratigraphic age of Elgaria is 16.7 Ma. Additionally, the geographic range of Elgaria is extended several hundred miles from the closest extant occurrence of the genus.
Yuichiro Hara, Miki Takeuchi, Yuka Kageyama, Kaori Tatsumi, Masahiko Hibi, Hiroshi Kiyonari & Shigehiro Kuraku (2018)
Madagascar ground gecko genome analysis characterizes asymmetric fates of duplicated genes.
BMC Biology 16:40
Conventionally, comparison among amniotes â birds, mammals, and reptiles â has often been approached through analyses of mammals and, for comparison, birds. However, birds are morphologically and physiologically derived and, moreover, some parts of their genomes are recognized as difficult to sequence and/or assemble and are thus missing in genome assemblies. Therefore, sequencing the genomes of reptiles would aid comparative studies on amniotes by providing more comprehensive coverage to help understand the molecular mechanisms underpinning evolutionary changes.
Herein, we present the whole genome sequences of the Madagascar ground gecko (Paroedura picta), a promising study system especially in developmental biology, and used it to identify changes in gene repertoire across amniotes. The genome-wide analysis of the Madagascar ground gecko allowed us to reconstruct a comprehensive set of gene phylogenies comprising 13,043 ortholog groups from diverse amniotes. Our study revealed 469 genes retained by some reptiles but absent from available genome-wide sequence data of both mammals and birds. Importantly, these genes, herein collectively designated as âelusiveâ genes, exhibited high nucleotide substitution rates and uneven intra-genomic distribution. Furthermore, the genomic regions flanking these elusive genes exhibited distinct characteristics that tended to be associated with increased gene density, repeat element density, and GC content.
This highly continuous and nearly complete genome assembly of the Madagascar ground gecko will facilitate the use of this species as an experimental animal in diverse fields of biology. Gene repertoire comparisons across amniotes further demonstrated that the fate of a duplicated gene can be affected by the intrinsic properties of its genomic location, which can persist for hundreds of millions of years.
James R. Super, Karen Chin, Mark Pagani, Hui Li & Pincelli M. Hull (2018)
Late Cretaceous climate in the Canadian Arctic: multi-proxy constraints from Devon Island.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
Arctic TEX86 sea surface temperatures of ~13â21âÂC in Late Cretaceous.
MBTâ5ME terrestrial temperature estimates of ~12â17âÂC.
Warm month bias of TEX86 suggested by biomarker analysis of marine coprolites.
Neritic salinity highly variable (10â30 PSU).
Isotopic composition of precipitation highly enriched relative to modern.
Arctic climate in the Late Cretaceous has long been recognized to have been warm and wet relative to the present, but quantitative assessments of paleoclimate have been challenging due, in part, to disagreements between proxies in marine and terrestrial environments. This study provides a first multiproxy evaluation of Late Cretaceous (~93â90âMa to 73â72âMa) paleoclimate and paleohydrology from Devon Island in the Canadian High Arctic (modern location: 76Â17â N, 91Â12âW; Late Cretaceous location: ~71Â30â N, ~24Â30âW). Surface temperatures are reconstructed at ~12.6 to 20.6âÂC for the ocean and 11.7 to 16.9âÂC over land, using glycerol dialkyl glycerol tetraether (GDGT) based proxies measured from marine (TEX86) and terrestrial samples (MBTâ5ME). These proxies are likely skewed towards warm month temperatures, based on novel analysis and interpretation of biomarkers in sediment and co-occurring marine vertebrate coprolites. The hydrogen isotopic composition (Î2H) of precipitation is constrained to have varied from â123â to â82â (VSMOW) using evidence from n-alkanes likely derived from higher plants. Î18O of shelfal marine surface water is constrained to have been between â10.5â to â3.4â, using phosphate oxygen isotopes of marine vertebrate teeth and coprolites. From these, marine salinity is modeled to have varied from 10 PSU and 30 PSU, indicative of periodic freshwater influx. These estimates indicate that large marine vertebrates lived and fed, at least intermittently, in near-shore brackish waters. Finally, the Arctic was similarly warm in both the Late Cretaceous and Paleocene/Eocene, but the Late Cretaceous isotopic composition of precipitation at Devon Island was enriched in the heavy isotope of hydrogen by up to +60 to +70â relative to Arctic Eocene sites. The combination of techniques used here reduces uncertainties related to the application of proxies to an environment without a modern analogue, providing novel paleoclimatic constraints on the Late Cretaceous Arctic region.
James D. Witts, Robert J. Newton, Benjamin J.W. Mills, Paul B. Wignall, Simon H.Bottrell, Joanna L.O.Hall, Jane E.Francis & Alistair Crame (2018)
The impact of the CretaceousâPaleogene (KâPg) mass extinction event on the global sulfur cycle: Evidence from Seymour Island, Antarctica
Geochimica et Cosmochimica Acta 230: 17-45
The CretaceousâPaleogene (KâPg) mass extinction event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69â65.5âMa) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69âMa), with some fluctuations that could be related to increased pyrite burial during the 'mid-Maastrichtian Event'. This is followed by an enigmatic +4â increase in Î34SCAS during the late Maastrichtian (68â66âMa), culminating in a peak in values in the immediate aftermath of the KâPg extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater Î34S of 3â4â suggests that a global decline in organic carbon burial related to collapse in export productivity, also impacted the sulfur cycle via a significant drop in pyrite burial. Box modelling suggests that to achieve an excursion of this magnitude, pyrite burial must be reduced by >15%, with a possible role for a short term increase in global weathering rates. Recovery of the sulfur cycle to pre-extinction values occurs at the same time (~320âkyrs) as initial carbon cycle recovery globally. These recoveries are also contemporaneous with an initial increase in local alpha diversity of marine macrofossil faunas, suggesting biosphere-geosphere links during recovery from the mass extinction. Modelling further indicates that concentrations of sulfate in the oceans must have been 2âmM, lower than previous estimates for the Late Cretaceous and Paleocene and an order of magnitude lower than today.