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1. The affinities of the Late Triassic Cryptovaranoides and the age of crown squamates

   https://doi.org/10.1098/rsos.230968  

   Brownstein, Chase D. ; Simões, Tiago R. ; Caldwell, Michael W. ; Lee, Michael S. ; Meyer, Dalton L. ; Scarpetta, Simon G. ( October 2023 , Royal Society Open Science)

   Most living reptile diversity is concentrated in Squamata (lizards, including snakes), which have poorly known origins in space and time. Recently, †Cryptovaranoides microlaniusfrom the Late Triassic of the United Kingdom was described as the oldest crown squamate. If true, this result would push back the origin of all major lizard clades by 30–65 Myr and suggest that divergence times for reptile clades estimated using genomic and morphological data are grossly inaccurate. Here, we use computed tomography scans and expanded phylogenetic datasets to re-evaluate the phylogenetic affinities of †Cryptovaranoidesand other putative early squamates. We robustly reject the crown squamate affinities of †Cryptovaranoides, and instead resolve †Cryptovaranoidesas a potential member of the bird and crocodylian total clade, Archosauromorpha. Bayesian total evidence dating supports a Jurassic origin of crown squamates, not Triassic as recently suggested. We highlight how features traditionally linked to lepidosaurs are in fact widespread across Triassic reptiles. Our study reaffirms the importance of critically choosing and constructing morphological datasets and appropriate taxon sampling to test the phylogenetic affinities of problematic fossils and calibrate the Tree of Life.

    

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2. The First Late Triassic Pistosaur from North America

   McGaughey, G ; Irmis, R ; Kelley, N ; Hodges, M ; Tackett, L ; Noble, P ( May 2023 , Geological Society of America Abstracts with Programs)

   Two recently discovered vertebrae collections from the Gabbs Formation in New York Canyon, Nevada, USA are among the first Late Triassic pistosauroid fossils reported from North America. Pistosauroidea were a group of long-necked secondarily aquatic reptiles that belong to the clade sauropterygia. Pistosauroids first evolved in the Triassic Period but later became an integral part of the Mesozoic marine ecosystem as the iconic plesiosaurs during the Jurassic and Cretaceous Periods. Our findings include a single small centrum from near the Triassic/Jurassic boundary and a block of similarly sized associated vertebrae from the early Rhaetian. The vertebrae exhibit a uniquely pistosauroid external morphology. The centrum is antero-posteriorly narrow but dorso-ventrally tall with gently amphicoelous faces. The histology revealed through micro-CT scanning, is also diagnostically pistosauroid. In sagittal cross-section, a denser layer of bone is visible along the faces of the centrum, while a unique V-shaped texture extending from the base of the neural canal is visible in transverse cross-section. The New York Canyon locality has long been renowned as a reference section for the Late Triassic and Triassic/Jurassic boundary but has only recently become a focus for vertebrate research. The Gabbs Formation at this locality is a relatively shallow marine environment and ranges from mid ramp to inner ramp. Vertebrate material has been noted throughout New York Canyon, nearly all of which has been identified as ichthyosaur, but these discoveries have shown the potential for the area as an important site for Late Triassic sauropterygians which have a poor record globally and were previously unknown from North America. Despite the limited nature of this new material, it is significant in providing evidence of the presence of pistosauroids in the Late Triassic of Eastern Panthalassa and helps fill in the exceptionally sparse history of sauropterygians in the Triassic of cordilleran North America. 

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3. Hematite reconstruction of Late Triassic hydroclimate over the Colorado Plateau

   https://doi.org/10.1073/pnas.2004343118  

   Lepre, Christopher J. ; Olsen, Paul E. ( February 2021 , Proceedings of the National Academy of Sciences)

   Hematite is the most abundant surficial iron oxide on Earth resulting from near-surface processes that make it important for addressing numerous geologic problems. While red beds have proved to be excellent paleomagnetic recorders, the early diagenetic origin of hematite in these units is often questioned. Here, we validate pigmentary hematite (“pigmentite”) as a proxy indicator for the Late Triassic environment and its penecontemporaneous origin by analyzing spectrophotometric measurements of a 14.5-My–long red bed sequence in scientific drill core CPCP-PFNP13-1A of the Chinle Formation, Arizona. Pigmentite concentrations in the red beds track the evolving pattern of the Late Triassic monsoon and indicate a long-term rise in aridity beginning at ∼215 Ma followed by increased oscillatory climate change at ∼213 Ma. These monsoonal changes are attributed to the northward drift of the Colorado Plateau as part of Laurentia into the arid subtropics during a time of fluctuating CO₂. Our results refine the record of the Late Triassic monsoon and indicate significant changes in rainfall proximal to the Adamanian–Revueltian biotic transition that thus may have contributed to apparent faunal and floral events at 216 to 213 Ma.

    

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4. Revision of the Late Triassic metoposaurid “ Metoposaurus ” bakeri (Amphibia: Temnospondyli) from Texas, USA and a phylogenetic analysis of the Metoposauridae

   https://doi.org/10.7717/peerj.14065  

   Gee, Bryan M. ; Kufner, Aaron M. ( January 2022 , PeerJ)

   Metoposaurids are a clade of large-bodied temnospondyls commonly found in non-marine Late Triassic deposits across northern Pangea. Three taxa are known from North America: Anaschisma browni , Apachesaurus gregorii , and “ Metoposaurus ” bakeri . While the osteology of most metoposaurids has been recently revised, that of a few taxa, including “ Metoposaurus ” bakeri remains poorly characterized. This taxon was formally described in 1931 as “ Buettneria bakeri ,” and its taxonomy has remained in flux ever since then. “ Metoposaurus ” bakeri is the earliest appearing metoposaurid in North America (Carnian of Texas), and Metoposaurus has frequently been utilized as an index taxon of the Otischalkian estimated holochron (‘land vertebrate faunachron’) and for biostratigraphic correlations with other geographic regions. The taxonomy of this species is therefore relevant for both taxonomic experts and biostratigraphers. Here we redescribe all material from the type locality of “ M .” bakeri , the Elkins Place bone bed, and perform a phylogenetic analysis using a revised matrix assembled from several previous studies. Anatomical comparisons and phylogenetic analyses do not support placement in either Metoposaurus , a taxon otherwise only found in Europe, or Anaschisma , the only other large-bodied taxon from North America. Therefore, we erect a new genus, Buettnererpeton gen. nov., to accommodate this species. Metoposaurus is consequently absent from North America, and this genus cannot be used in global biostratigraphy. Phylogenetic analyses provide evidence that the phylogeny of the Metoposauridae remains extremely labile, with drastic differences in topological resolution and structure being linked to just a handful of characters and scores. Metoposaurids’ morphological conservatism and the increased recognition of intraspecific variation thus continue to be major confounds to elucidating the evolutionary history of this clade. 

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5. AN ENVIRONMENTAL BASELINE TO THE END-TRIASSIC CARBONATE CRISIS: LATE TRIASSIC FACIES OF THE GABBS FORMATION (NEVADA, USA)

   https://doi.org/10.1130/abs/2020AM-358393  

   Clement, Annaka M. ; Tackett, Lydia ( January 2020 , Geological Society of America Abstracts with Programs)

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