Ben Creisler
Some recent tetrapod papers:
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A. Guerrero & A. PÃrez-GarcÃa (2021)
Morphological variability and shell characterization of the European uppermost Jurassic to lowermost Cretaceous stem turtle Pleurosternon bullockii (Paracryptodira, Pleurosternidae)
Cretaceous Research 104872
doi:
https://doi.org/10.1016/j.cretres.2021.104872
Highlights
An exceptionally high number of shells are identified for Pleurosternon bullockii.
The lack of studies on its shell limited knowledge about this aquatic stem turtle.
This form is redefined here, high shell morphological variability being recognized.
The study of the variability is performed by qualitative and quantitative approaches.
A great number of polymorphic characters and two sexual dimorphs are identified.
ABSTRACT
The British taxon Pleurosternon bullockii corresponds to the best represented member of Pleurosternidae, this lineage of Paracryptodira being the only one of aquatic basal turtles (stem Testudines) identified in both the Upper Jurassic and the Lower Cretaceous records of Europe. Despite the high number of available specimens of Pleurosternon bullockii, most of them found more than a century ago, the vast majority remained unpublished or poorly studied. A detailed study of the morphological variability in the shell of Pleurosternon bullockii is carried out here for the first time. It is based on the study of around sixty specimens from the British record, the vast majority from the Berriasian. The availability of so many specimens, most of them very well-preserved, is unique for a European Lower Cretaceous turtle, but also exceptional for the Mesozoic record worldwide. In this way, its shell anatomy can be characterized in detail, based on both qualitative and quantitative studies. A landmark-based geometric morphometric method has been applied to develop the quantitative approach, as well as several statistical techniques in order to extensively identify and characterize the shell elements affected by a greater range of variability. The results evidence a significant range of the shape variability for several elements at the mature stage of Pleurosternon bullockii, regarding both polymorphisms as well as sexual dimorphism. Several shell characters of this form are characterized for the first time or reinterpreted, and an amended diagnosis for the reference taxon of the clade Pleurosternidae is proposed.
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A new species of pelomedusoid turtle: Elkanemys pritchardi gen. et sp. nov. from Upper Cretaceous (Cenomanian) is described. The specimen MMCH-PV 73 outcrops at Lago Ezequiel Ramos Mexia, near El ChocÃn town, RÃo Negro Province, Argentina. The holotype is only represented by a partial carapace and plastron, which has been included in a cladistic analysis, resulting Elkanemys pritchardi as a member of Cearachelyini tribe of the clade Bothremydidae. This new taxon corresponds to the first record of a Bothremydidae in a Cretaceous horizon of NeuquÃn Basin. The results here presented highlight the diversity of Pelomedusoides in the Cretaceous of Patagonia allowing the inclusion of this area in further paleobiogeographic history of Bothremydidae clade.
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Highlights
Permian Hyloidichnus tracks from the Luc Basin of France.
Exceptional Hyloidichnus trackways showing continuous tail and digit drag traces.
First correlation between Hyloidichnus trackways and captorhinomorphs trackmakers.
Inference of a complete locomotor cycle of captorhinomorph eureptiles.
Tracks increase our knowledge of Permian tetrapod locomotion.
Abstract
Newly discovered tetrapod footprints from the middle Permian Pelitic Formation of Gonfaron (Le Luc Basin, Var, France) are described in detail and assigned to the ichnogenus Hyloidichnus. These specimens are very well-preserved, with detailed trackways showing anatomical features, digit drag traces and continuous tail impressions. Together with other Hyloidichnus specimens from the same locality and from the University of Burgundy collections, they allow the identification of the possible trackmakers of Hyloidichnus: small Hyloidichnus footprints are correlated with captorhinomorphs with autopodia similar to Captorhinus whereas large Hyloidichnus footprints might be correlated with larger captorhinomorphs or other âbasalâ (eventually stem-) moradisaurines. A detailed comparative analysis is proposed to better understand the locomotion style of the trackmakers. Starting from the reconstruction of the stance phase of Captorhinus, we document the swing phase of the fore- and hind-limbs of captorhinomorphs thanks to the continuous digit drag traces associated with Hyloidichnus. A link between gait and track preservation have been highlighted through the analysis of tail impressions and high-resolution 3D models. In all, this study increases our understanding of captorhinomorph locomotion and enhances the integration of both tracks and skeletal remains to highlight the biomechanics of Permian tetrapods.
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Miriam A. Slodownik, Thomas MÃrs & Benjamin P. Kear (2021)
Reassessment of the Early Triassic trematosaurid temnospondyl Tertrema acuta from the Arctic island of Spitsbergen.
Journal of Vertebrate Paleontology Article: e1900209
doi:
https://doi.org/10.1080/02724634.2021.1900209 https://www.tandfonline.com/doi/full/10.1080/02724634.2021.1900209Trematosaurids were globally distributed Early Triassic temnospondyl amphibians characterized by elongate 'crocodile-like' skulls. Some of the most famous trematosaurid fossils were discovered on the island of Spitsbergen in the Arctic Svalbard archipelago. Among these, the short-snouted trematosaurine, Tertrema acuta, is one of the few taxa represented by virtually complete cranial remains. Unusually, however, the type specimens comprise only natural molds that were historically used to reconstruct three-dimensional casts. Here, we re-assess these restorations using the original impressions to phylogenetically analyze and re-diagnose the taxon. Unexpectedly, our first-hand scores differ markedly from previous literature-sourced interpretations and yield conflicting tree topologies that nest T. acuta with long-snouted lonchorhynchines, thus destabilizing the long-favored sub-division of trematosaurids based on their skull shape. We attribute this result to character state conflict and suggest that the traditional classification of trematosaurids may mask more complex evolutionary relationships, as well as possible trophic partitioning, and eco-morphological plasticity.
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Steven L. Wick (2021)
Fossil frogs from the early Campanian of West Texas, USA, with comments on Late Cretaceous anuran diversity in southern Laramidia.
Palaeobiodiversity and Palaeoenvironments (advance online publication)
DOI:
https://doi.org/10.1007/s12549-021-00481-4https://link.springer.com/article/10.1007/s12549-021-00481-4A rare early Campanian (Aquilan) assemblage consisting of disarticulated anuran bones is described from the Aguja Formation of West Texas, USA. Many specimens within the assemblage pertain to taxonomically informative elements (maxillae, urostyles, and ilia). Morphological variety among specimens pertaining to each suggests high local species richness comparable with that seen elsewhere among frogs from similarly well-sampled localities of the Late Cretaceous Western Interior. Comparison between environmentally and temporally analogous microvertebrate assemblages in southern Utah, USA, reveals that anurans in both areas exhibit morphological similarities consistent with regionally allied âsouthernâ faunas. Among their differences, one character (dorsal protuberance of the ilium) consistently exhibited among some ilial morphotypes from Utah is conspicuously absent among those of West Texas. Two ostensibly exclusive ilial morphs in West Texas add additional support to the presence of taxonomically segregated, sub-regional populations of anurans in southern Laramidia during early to middle Campanian time.
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Secondary aquatic vertebrates exhibit a diversity of swimming modes that use paired limbs and/or the tail. Various secondarily aquatic tetrapod clades, including amphibians, reptiles, and mammals employ transverse undulations or oscillations of the tail for swimming. These movements have often been classified according to a kinematic gradient that was established for fishes, but may not be appropriate to describe the swimming motions of tetrapods. To understand the evolution of movements and design of the tail in aquatic tetrapods, we categorize the types of tails used for swimming and examine swimming kinematics and hydrodynamics. From a foundation of a narrow, elongate ancestral tail, the tails used for swimming by aquatic tetrapods are classified as tapered, keeled, paddle, and lunate. Tail undulations are associated with tapered, keeled, and paddle tails for a diversity of taxa. Propulsive undulatory waves move down the tail with increasing amplitude toward the tail tip, while moving posteriorly at a velocity faster than the anterior motion of the body indicating that the tail is used for thrust generation. Aquatic propulsion is associated with the transfer of momentum to the water from the swimming movements of the tail, particularly at the trailing edge. The addition of transverse extensions and flattening of the tail increases the mass of water accelerated posteriorly and affects vorticity shed into the wake for more aquatically adapted animals. DPIV (Digital Particle Image Velocimetry) reveals differences were exhibited in the vortex wake between the morphological and kinematic extremes of the alligator with a tapering undulating tail and the dolphin with oscillating wing-like flukes that generate thrust. In addition to exploring the relationship between shape of undulating tails and swimming performance across aquatic tetrapods, the role of tail reduction or loss of a tail in aquatic-tetrapod swimming was also explored. For aquatic tetrapods, reduction would have been due to factors including locomotor and defensive specializations and phylogenetic and physiological constraints. Possession of a thrust-generating tail for swimming, or lack thereof, guided various lineages of secondarily aquatic vertebrates into different evolutionary trajectories for effective aquatic propulsion (i.e., speed, efficiency, acceleration).
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NOTE: This paper was posted yesterday on the DML but now has a free pdf:
Free pdf: