Ben Creisler
Some recent non-dino papers:
Regurgitalites (fossilized regurgitates) can provide insight into the behavioral ecology and physiology of extinct species but they are rarely reported because they are difficult to identify and distinguish from coprolites. A compact mass of skeletal material from the Owl Rock Member of the Upper Triassic Chinle Formation of Arizona reveals features that identify it as a regurgitalite. Characteristics of the teeth and osteoderms in the specimen indicate that these remains belong to the pseudosuchian archosaur Revueltosaurus. Chemical and microstructural analysis revealed a dearth of gastric etching, the preservation of muscle fibers, and the absence of a phosphatic matrix, indicating that this bone mass is a regurgitalite and not a coprolite. It was probably produced by a phytosaur, rauisuchid, or temnospondyl, all of which occur in the Owl Rock Member. We offer an identification key to assist in distinguishing between different types of digestive remains produced by vertebrate carnivores.
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Richard Cloutier, Alice M. Clement, Michael S. Y. Lee, Roxanne NoÃl, Isabelle BÃchard, Vincent Roy & John A. Long (2020)
The evolution of fishes to tetrapods (four-limbed vertebrates) was one of the most important transformations in vertebrate evolution. Hypotheses of tetrapod origins rely heavily on the anatomy of a few tetrapod-like fish fossils from the Middle and Late Devonian period (393â359 million years ago). These taxa--known as elpistostegalians--include Panderichthys, Elpistostege and Tiktaalik, none of which has yet revealed the complete skeletal anatomy of the pectoral fin. Here we report a 1.57-metre-long articulated specimen of Elpistostege watsoni from the Upper Devonian period of Canada, which represents--to our knowledge--the most complete elpistostegalian yet found. High-energy computed tomography reveals that the skeleton of the pectoral fin has four proximodistal rows of radials (two of which include branched carpals) as well as two distal rows that are organized as digits and putative digits. Despite this skeletal pattern (which represents the most tetrapod-like arrangement of bones found in a pectoral fin to date), the fin retains lepidotrichia (fin rays) distal to the radials. We suggest that the vertebrate hand arose primarily from a skeletal pattern buried within the fairly typical aquatic pectoral fin of elpistostegalians. Elpistostege is potentially the sister taxon of all other tetrapods, and its appendages further blur the line between fish and land vertebrates.
News:
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Gen Morinaga and Philip J. Bergmann (2020)
Evolution of fossorial locomotion in the transition from tetrapod to snake-like in lizards.
Proceedings of the Royal Society B: Biological Sciences 287(1923): 20200192
doi:
https://doi.org/10.1098/rspb.2020.0192https://royalsocietypublishing.org/doi/10.1098/rspb.2020.0192
Dramatic evolutionary transitions in morphology are often assumed to be adaptive in a new habitat. However, these assumptions are rarely tested because such tests require intermediate forms, which are often extinct. In vertebrates, the evolution of an elongate, limbless body is generally hypothesized to facilitate locomotion in fossorial and/or cluttered habitats. However, these hypotheses remain untested because few studies examine the locomotion of species ranging in body form from tetrapod to snake-like. Here, we address these functional hypotheses by testing whether trade-offs exist between locomotion in surface, fossorial and cluttered habitats in Australian Lerista lizards, which include multiple intermediate forms. We found that snake-like species penetrated sand substrates faster than more lizard-like species, representing the first direct support of the adaptation to fossoriality hypothesis. By contrast, body form did not affect surface locomotion or locomotion through cluttered leaf litter. Furthermore, all species with hindlimbs used them during both fossorial and surface locomotion. We found no evidence of a trade-off between fossorial and surface locomotion. This may be either because Lerista employed kinematic strategies that took advantage of both axial- and limb-based propulsion. This may have led to the differential occupation of their habitat, facilitating diversification of intermediate forms.
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Free pdf:
Robert A. Gastaldo, Sandra L. Kamo, Johann Neveling, John W. Geissman, Cindy V. Looy & Anna M. Martini (2020)
The base of the Lystrosaurus Assemblage Zone, Karoo Basin, predates the end-Permian marine extinction.
Nature Communications 11, Article number: 1428
doi:
https://doi.org/10.1038/s41467-020-15243-7 https://www.nature.com/articles/s41467-020-15243-7Free pdf:
https://www.nature.com/articles/s41467-020-15243-7.pdfThe current model for the end-Permian terrestrial ecosystem crisis holds that systematic loss exhibited by an abrupt turnover from the Daptocephalus to the Lystrosaurus Assemblage Zone (AZ; Karoo Basin, South Africa) is time equivalent with the marine PermianâTriassic boundary (PTB). The marine event began at 251.941âÂâ0.037âMa, with the PTB placed at 251.902âÂâ0.024âMa (2Ï). Radio-isotopic dates over this interval in the Karoo Basin were limited to one high resolution ash-fall deposit in the upper Daptocephalus AZ (253.48âÂâ0.15 (2Ï) Ma) with no similar age constraints for the overlying biozone. Here, we present the first U-Pb CA-ID-TIMS zircon age (252.24âÂâ0.11 (2Ï) Ma) from a pristine ash-fall deposit in the Karoo Lystrosaurus AZ. This date confirms that the lower exposures of the Lystrosaurus AZ are of latest Permian age and that the purported turnover in the basin preceded the end-Permian marine event by over 300 ka, thus refuting the previously used stratigraphic marker for terrestrial end-Permian extinction.
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