Eunotosaurus labyrinth morphology + Early Triassic marine ecosystem coprolites + stem tetrapod limbs musculoskeletal function
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Ben Creisler
Mar 30, 2026, 1:42:51 PM (4 days ago) Mar 30
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Ben Creisler
Julia L. Molnar, John R. Hutchinson & Stephanie E. Pierce (2026)
Musculoskeletal function of stem tetrapod limbs
Palaeontology 69(2): e70049
doi: https://doi.org/10.1111/pala.70049
https://onlinelibrary.wiley.com/doi/10.1111/pala.70049
The tetrapod water–land transition has been studied for more than a century, but questions about the locomotor function of early tetrapod limbs still remain. The limb and girdle skeletons of stem tetrapods are morphologically distinct from those of crown tetrapods, probably resulting in differences in range of motion and muscle leverage. To test hypotheses about their limb function, we built three-dimensional musculoskeletal models of the stem tetrapods Acanthostega (Devonian) and Pederpes (Carboniferous), and of an extant salamander and lizard for comparison. We predicted that the joints of stem tetrapods would not be able to accommodate the full range of movements used by extant tetrapods during terrestrial walking, and that stem tetrapods would have less muscle leverage for resisting vertical forces and for hindlimb-based propulsion. As expected, hip and shoulder mobility in the two stem tetrapods was incompatible with the kinematic patterns used by extant sprawling tetrapods. In contrast, their hip and shoulder depression muscle moment arms were similar to or greater than those of the crown tetrapods, and retraction moment arms were similar between the hip and shoulder in all four tetrapods, showing little evidence that the limbs of stem tetrapods were less adapted for weight support or HL-driven locomotion. However, the moment arm results were sensitive to methodological choices such as joint angles and normalization. Comparison with additional extinct and extant tetrapods with different locomotor strategies could clarify how muscle moment arms are related to limb mechanics and aquatic versus terrestrial locomotion.
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New papers:
Serjoscha W. Evers, Eldon Panigot, Holger Petermann, Bruce S. Rubidge, Gabriel S. Bever & Tyler R. Lyson (2026)
Labyrinth morphology of Eunotosaurus africanus in the context of semicircular canal shape variation across amniotes
Journal of Systematic Palaeontology 24(1): 2634330
doi: https://doi.org/10.1080/14772019.2026.2634330
https://www.tandfonline.com/doi/full/10.1080/14772019.2026.2634330
Free pdf:
https://www.tandfonline.com/doi/epdf/10.1080/14772019.2026.2634330
The Middle Permian reptile Eunotosaurus africanus is a key taxon for understanding reptile evolution because it has been proposed to be one of the earliest stem turtles, but it could alternatively represent an early sauropsid. Alternative evolutionary interpretations are based on morphological character observations, and comparative anatomy of previously undocumented body parts may yield novel character evidence. Based on a previously unreported specimen of Eunotosaurus africanus, we provide descriptions of its inner ear anatomy, which we compare to a diversity of amniotes including turtles, millerettids and novel segmentations of Youngina capensis and Champsosaurus lindoei. The inner ear of Eunotosaurus africanus has plesiomorphic neodiapsid inner ear features that contrast with turtle ear morphology, including a radius of curvature of the anterior semicircular canal (ASC) that is larger than that of the posterior semicircular canal (PSC), narrow intercanal angles, slender vertical semicircular canals, and a bend in the central section of the PSC. Eunotosaurus africanus shares with turtles a large common crus cross-section and a thickened lateral semicircular canal. We provide a landmark-based comparison of amniote labyrinth shapes, which shows principal differences in the semicircular canals of birds, mammals and turtles as end members of a gradient of semicircular canal geometries. Other extant amniote groups (crocodiles, lepidosaurs), fossil lineages (e.g. sauropterygians, captorhinids, millerettids, younginiforms, varanopids, Eunotosaurus africanus) and stem lineages of extant groups (e.g. pterosaurs, non-avian dinosaurs, phytosaurs, other extinct pseudosuchians, mosasaurs, ‘pelycosaurs’, dicynodonts) show semicircular canal geometries that are generally intermediate between extreme shapes of birds, mammals and turtles, so that the entire morphospace shows gradational morphologies. The observed variation provides evidence of convergent evolution of labyrinth features, but also suggests phylogenetic signal is widespread in labyrinth morphology and that bird, mammal, and turtle labyrinth shapes may have evolved from a plesiomorphic shape that was retained in many reptilian stem lineages.
=====
Free pdf:
Serjoscha W. Evers, Eldon Panigot, Holger Petermann, Bruce S. Rubidge, Gabriel S. Bever & Tyler R. Lyson (2026)
Labyrinth morphology of Eunotosaurus africanus in the context of semicircular canal shape variation across amniotes
Journal of Systematic Palaeontology 24(1): 2634330
doi: https://doi.org/10.1080/14772019.2026.2634330
https://www.tandfonline.com/doi/full/10.1080/14772019.2026.2634330
Free pdf:
https://www.tandfonline.com/doi/epdf/10.1080/14772019.2026.2634330
The Middle Permian reptile Eunotosaurus africanus is a key taxon for understanding reptile evolution because it has been proposed to be one of the earliest stem turtles, but it could alternatively represent an early sauropsid. Alternative evolutionary interpretations are based on morphological character observations, and comparative anatomy of previously undocumented body parts may yield novel character evidence. Based on a previously unreported specimen of Eunotosaurus africanus, we provide descriptions of its inner ear anatomy, which we compare to a diversity of amniotes including turtles, millerettids and novel segmentations of Youngina capensis and Champsosaurus lindoei. The inner ear of Eunotosaurus africanus has plesiomorphic neodiapsid inner ear features that contrast with turtle ear morphology, including a radius of curvature of the anterior semicircular canal (ASC) that is larger than that of the posterior semicircular canal (PSC), narrow intercanal angles, slender vertical semicircular canals, and a bend in the central section of the PSC. Eunotosaurus africanus shares with turtles a large common crus cross-section and a thickened lateral semicircular canal. We provide a landmark-based comparison of amniote labyrinth shapes, which shows principal differences in the semicircular canals of birds, mammals and turtles as end members of a gradient of semicircular canal geometries. Other extant amniote groups (crocodiles, lepidosaurs), fossil lineages (e.g. sauropterygians, captorhinids, millerettids, younginiforms, varanopids, Eunotosaurus africanus) and stem lineages of extant groups (e.g. pterosaurs, non-avian dinosaurs, phytosaurs, other extinct pseudosuchians, mosasaurs, ‘pelycosaurs’, dicynodonts) show semicircular canal geometries that are generally intermediate between extreme shapes of birds, mammals and turtles, so that the entire morphospace shows gradational morphologies. The observed variation provides evidence of convergent evolution of labyrinth features, but also suggests phylogenetic signal is widespread in labyrinth morphology and that bird, mammal, and turtle labyrinth shapes may have evolved from a plesiomorphic shape that was retained in many reptilian stem lineages.
=====
Mingtao Yao, Zuoyu Sun, Yinuo Wang, Zhaoliang Ma, Torsten Scheyer, Cheng Ji, Shuang Liu, Jiandong Huang & Dayong Jiang (2026)
Coprolite evidence for trophic reorganization of Early Triassic marine ecosystem after the Permian–Triassic mass extinction
Global and Planetary Change 105456
doi: https://doi.org/10.1016/j.gloplacha.2026.105456
https://www.sciencedirect.com/science/article/abs/pii/S0921818126001773
Highlights
Coprolites reveal trophic reorganization after the Permian–Triassic extinction.
Marine reptiles rapidly occupied high trophic levels after the extinction.
Trophic recovery following the PTME was regionally heterogeneous.
Early Triassic food web can be predator-rich but prey-limited.
Abstract
Reconstruction of marine trophic architecture is fundamental for understanding the Earth system recovery following the Permian–Triassic mass extinction (PTME). The Early Triassic Chaohu Fauna (~248.7 Ma) represents one of the oldest documented marine reptile assemblages, yet direct ecological evidence for its trophic structure remains limited. We present the first systematic analysis of over 500 coprolites from the Nanlinghu Formation at Chaohu, China. Through multidisciplinary investigation, we identify five coprolite morphotypes and twelve subtypes, and document size-dependent inclusion patterns. Conodont elements and coleoid arm hooks occur almost exclusively in small coprolites, whereas most large specimens lack any recognizable inclusions, and rare specimens contain teeth of durophagous fishes or other vertebrate debris. Multiple lines of evidence suggest that invertebrates generated the smallest forms, whereas larger cylindrical forms were produced chiefly by marine reptiles. The coprolite record reveals a multi-tiered trophic structure in which marine reptiles had already occupied meso- and apex consumer roles by the Early Triassic. Frequent occurrence of conodonts and coleoid arm hooks in small coprolites indicates that these taxa constituted a routinely consumed but previously underestimated component. The widespread absence of hard-part residues in vertebrate coprolites supports a diversified dietary spectrum among marine reptiles, including soft-prey specialization, durophagy, and piscivory. Comparison with other Early Triassic marine ecosystems highlights pronounced regional heterogeneity in trophic recovery. These results demonstrate that the Chaohu Fauna captures an early stage of reptile-dominated trophic reorganization and represents a predator-rich but prey-constrained ecosystem during post-extinction recovery.
Coprolite evidence for trophic reorganization of Early Triassic marine ecosystem after the Permian–Triassic mass extinction
Global and Planetary Change 105456
doi: https://doi.org/10.1016/j.gloplacha.2026.105456
https://www.sciencedirect.com/science/article/abs/pii/S0921818126001773
Highlights
Coprolites reveal trophic reorganization after the Permian–Triassic extinction.
Marine reptiles rapidly occupied high trophic levels after the extinction.
Trophic recovery following the PTME was regionally heterogeneous.
Early Triassic food web can be predator-rich but prey-limited.
Abstract
Reconstruction of marine trophic architecture is fundamental for understanding the Earth system recovery following the Permian–Triassic mass extinction (PTME). The Early Triassic Chaohu Fauna (~248.7 Ma) represents one of the oldest documented marine reptile assemblages, yet direct ecological evidence for its trophic structure remains limited. We present the first systematic analysis of over 500 coprolites from the Nanlinghu Formation at Chaohu, China. Through multidisciplinary investigation, we identify five coprolite morphotypes and twelve subtypes, and document size-dependent inclusion patterns. Conodont elements and coleoid arm hooks occur almost exclusively in small coprolites, whereas most large specimens lack any recognizable inclusions, and rare specimens contain teeth of durophagous fishes or other vertebrate debris. Multiple lines of evidence suggest that invertebrates generated the smallest forms, whereas larger cylindrical forms were produced chiefly by marine reptiles. The coprolite record reveals a multi-tiered trophic structure in which marine reptiles had already occupied meso- and apex consumer roles by the Early Triassic. Frequent occurrence of conodonts and coleoid arm hooks in small coprolites indicates that these taxa constituted a routinely consumed but previously underestimated component. The widespread absence of hard-part residues in vertebrate coprolites supports a diversified dietary spectrum among marine reptiles, including soft-prey specialization, durophagy, and piscivory. Comparison with other Early Triassic marine ecosystems highlights pronounced regional heterogeneity in trophic recovery. These results demonstrate that the Chaohu Fauna captures an early stage of reptile-dominated trophic reorganization and represents a predator-rich but prey-constrained ecosystem during post-extinction recovery.
===
Julia L. Molnar, John R. Hutchinson & Stephanie E. Pierce (2026)
Musculoskeletal function of stem tetrapod limbs
Palaeontology 69(2): e70049
doi: https://doi.org/10.1111/pala.70049
https://onlinelibrary.wiley.com/doi/10.1111/pala.70049
The tetrapod water–land transition has been studied for more than a century, but questions about the locomotor function of early tetrapod limbs still remain. The limb and girdle skeletons of stem tetrapods are morphologically distinct from those of crown tetrapods, probably resulting in differences in range of motion and muscle leverage. To test hypotheses about their limb function, we built three-dimensional musculoskeletal models of the stem tetrapods Acanthostega (Devonian) and Pederpes (Carboniferous), and of an extant salamander and lizard for comparison. We predicted that the joints of stem tetrapods would not be able to accommodate the full range of movements used by extant tetrapods during terrestrial walking, and that stem tetrapods would have less muscle leverage for resisting vertical forces and for hindlimb-based propulsion. As expected, hip and shoulder mobility in the two stem tetrapods was incompatible with the kinematic patterns used by extant sprawling tetrapods. In contrast, their hip and shoulder depression muscle moment arms were similar to or greater than those of the crown tetrapods, and retraction moment arms were similar between the hip and shoulder in all four tetrapods, showing little evidence that the limbs of stem tetrapods were less adapted for weight support or HL-driven locomotion. However, the moment arm results were sensitive to methodological choices such as joint angles and normalization. Comparison with additional extinct and extant tetrapods with different locomotor strategies could clarify how muscle moment arms are related to limb mechanics and aquatic versus terrestrial locomotion.
===
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