Mesenosaurus (Early Permian varanopid) ankle morphology + Upper Jurassic turtle shell pathologies + vertebrate encephalization
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Ben Creisler
Nov 17, 2025, 3:53:45 PM (10 days ago) Nov 17
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Ben Creisler
Recent papers:
D. C. T. Rowe, J. M. Young, B. P. Boyd, J. J. Bevitt & R. R. Reisz (2025)
Appendicular morphology of Mesenosaurus efremovi and the earliest occurrence of a calcaneal tuberosity
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2586223
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2586223
The Richards Spur locality in Oklahoma, U.S.A. is renowned for its diverse assemblage of early Permian terrestrial tetrapods, including the varanopid Mesenosaurus efremovi. Recent quarrying operations yielded numerous skeletal remains attributed to this taxon, including partially articulated cranial and postcranial remains with the latter being especially important given the comparatively minimal description in previous studies. The specimens used in this study, including a superbly preserved hindfoot, all represent approximately the same growth stage, and collectively reveal the morphology of the entire pelvis and hindlimb in unprecedented detail. CT data, analysed using the segmentation software Avizo, was utilised to examine the hindfoot specimen. As in other varanopids, the limb proportions of this predator are gracile, the bones being more slender than in the similarly well-known taxon Varanops. In addition, M. efremovi exhibits unique ankle morphologies including a highly robust astragalus with a massive transverse ridge and a medially oriented tibial articular surface, a pronounced lateral calcaneal tuberosity and an enlarged fourth tarsal. These likely diagnostic features of Mesenosaurus point to specialised lower limb design for rapid locomotion, and further confirms its close relationship to the middle Permian M. romeri from Russia and consequent temporal longevity of this varanopid genus.
Appendicular morphology of Mesenosaurus efremovi and the earliest occurrence of a calcaneal tuberosity
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2586223
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2586223
The Richards Spur locality in Oklahoma, U.S.A. is renowned for its diverse assemblage of early Permian terrestrial tetrapods, including the varanopid Mesenosaurus efremovi. Recent quarrying operations yielded numerous skeletal remains attributed to this taxon, including partially articulated cranial and postcranial remains with the latter being especially important given the comparatively minimal description in previous studies. The specimens used in this study, including a superbly preserved hindfoot, all represent approximately the same growth stage, and collectively reveal the morphology of the entire pelvis and hindlimb in unprecedented detail. CT data, analysed using the segmentation software Avizo, was utilised to examine the hindfoot specimen. As in other varanopids, the limb proportions of this predator are gracile, the bones being more slender than in the similarly well-known taxon Varanops. In addition, M. efremovi exhibits unique ankle morphologies including a highly robust astragalus with a massive transverse ridge and a medially oriented tibial articular surface, a pronounced lateral calcaneal tuberosity and an enlarged fourth tarsal. These likely diagnostic features of Mesenosaurus point to specialised lower limb design for rapid locomotion, and further confirms its close relationship to the middle Permian M. romeri from Russia and consequent temporal longevity of this varanopid genus.
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Free pdf:
Daniel Tyborowski and Gabriela Sienkiewicz (2025)
Palaeopathologies in Upper Jurassic turtle shells – their origin and significance for the evolution of biotic interactions
Lethaia 58(4): 1–9
doi: https://doi.org/10.18261/let.58.4.4
https://www.scup.com/doi/10.18261/let.58.4.4
Free pdf:
https://www.scup.com/doi/epdf/10.18261/let.58.4.4
The study of bioerosion traces on the carapaces of Upper Jurassic turtles from Krzyżanowice, located in the northeastern margin of the Holy Cross Mountains in Poland, sheds light on the complex biotic interactions and palaeoecological dynamics of Mesozoic ecosystems. The research focuses on enigmatic pathologies observed on the turtle shells, combining histological, morphological, and palaeoenvironmental analyses to explore their origins and significance. Evidence of bone remodelling within the pathologies strongly supports their formation during the life of the turtles, suggesting interactions such as parasitism, symbiosis, and failed predation attempts. The variability in pathologies morphology—ranging from shallow, smooth-bottomed depressions to deep, irregular cavities—points to a diversity of bioeroders, including echinoids, microbial colonizers, and scavenging invertebrates. While remodelling suggests live damage in many cases, post-mortem bioerosion may have also contributed to the traces, particularly in low-energy, shallow marine environments. The findings highlight turtles as ecological hubs, playing vital roles as both substrates and participants in complex biotic interactions. Over geological time, a shift from symbiotic and parasitic traces to predation-related marks reflects changing ecological pressures and predator specialization. This study underscores the importance of turtles as indicators of palaeoenvironmental conditions and as resilient components of their ecosystems, capable of surviving repeated interactions with other organisms. By integrating modern analogs and fossil evidence, this research provides new perspectives on the evolutionary and ecological significance of bioerosion in the fossil record.
Not yet mentioned:
Free pdf:
Zitan Song, Michael Griesser, and Carel P. van Schaik (2025)
Parental investment and body temperature explain encephalization in vertebrates
Proceedings of the National Academy of Sciences 122(45): e2506145122
doi: https://doi.org/10.1073/pnas.2506145122
https://www.pnas.org/doi/10.1073/pnas.2506145122
Free pdf:
https://www.pnas.org/doi/epdf/10.1073/pnas.2506145122
Significance
Larger brains generally improve sensory, motor, and cognitive functioning, but this does not explain why brain size shows marked variation across vertebrate classes and increased over evolutionary time in some classes but not others. This pattern suggests that brain size expansion is affected by taxonomy-dependent costs or constraints. These are the focus of the expensive brain hypothesis, for which evidence has already been found in some taxa. Here, we systematically test two of its main predictions across all vertebrate classes and identify two conditions that together provide a coherent theoretical explanation for the well-known pattern in vertebrates brain size: 1) opportunities for greater parental investment into individual offspring, and 2) opportunities for stably increased brain temperatures.
Abstract
The systematic variation in relative brain size among vertebrate classes remains poorly understood. Here, based on the expensive brain hypothesis, we propose that two broad constraints explain much of the variation: 1) the ability to produce large offspring, and so provide them with the energy required for constructing larger brains, and 2) the ability to sustain continuously high body temperatures, because cooler and varying brain temperatures reduce brain performance and thus fitness. We therefore predicted that encephalization (major evolutionary increases in brain size) only happened where changes in physiology or natural history created these abilities. First, comparative analyses across all major vertebrate classes (n = 2600 species) revealed that protecting or provisioning eggs or embryos is associated with larger newborns. Subsequent analyses at the class level confirmed that newborn size and adult brain size underwent correlated evolution in birds, mammals, and cartilaginous fishes, but not in other fishes, amphibians, and reptiles. Second, we found a positive relationship between mean body temperature and brain size within each class (albeit sometimes insignificant). Third, a combined analysis across all vertebrates revealed a positive interaction between the effects of body temperature and newborn size. In conclusion, encephalization became most pronounced in vertebrate lineages that can both produce large offspring, reflecting internal fertilization with matrotrophy, and sustain high body temperature, partly linked to endothermy.
===
Free pdf:
Zitan Song, Michael Griesser, and Carel P. van Schaik (2025)
Parental investment and body temperature explain encephalization in vertebrates
Proceedings of the National Academy of Sciences 122(45): e2506145122
doi: https://doi.org/10.1073/pnas.2506145122
https://www.pnas.org/doi/10.1073/pnas.2506145122
Free pdf:
https://www.pnas.org/doi/epdf/10.1073/pnas.2506145122
Significance
Larger brains generally improve sensory, motor, and cognitive functioning, but this does not explain why brain size shows marked variation across vertebrate classes and increased over evolutionary time in some classes but not others. This pattern suggests that brain size expansion is affected by taxonomy-dependent costs or constraints. These are the focus of the expensive brain hypothesis, for which evidence has already been found in some taxa. Here, we systematically test two of its main predictions across all vertebrate classes and identify two conditions that together provide a coherent theoretical explanation for the well-known pattern in vertebrates brain size: 1) opportunities for greater parental investment into individual offspring, and 2) opportunities for stably increased brain temperatures.
Abstract
The systematic variation in relative brain size among vertebrate classes remains poorly understood. Here, based on the expensive brain hypothesis, we propose that two broad constraints explain much of the variation: 1) the ability to produce large offspring, and so provide them with the energy required for constructing larger brains, and 2) the ability to sustain continuously high body temperatures, because cooler and varying brain temperatures reduce brain performance and thus fitness. We therefore predicted that encephalization (major evolutionary increases in brain size) only happened where changes in physiology or natural history created these abilities. First, comparative analyses across all major vertebrate classes (n = 2600 species) revealed that protecting or provisioning eggs or embryos is associated with larger newborns. Subsequent analyses at the class level confirmed that newborn size and adult brain size underwent correlated evolution in birds, mammals, and cartilaginous fishes, but not in other fishes, amphibians, and reptiles. Second, we found a positive relationship between mean body temperature and brain size within each class (albeit sometimes insignificant). Third, a combined analysis across all vertebrates revealed a positive interaction between the effects of body temperature and newborn size. In conclusion, encephalization became most pronounced in vertebrate lineages that can both produce large offspring, reflecting internal fertilization with matrotrophy, and sustain high body temperature, partly linked to endothermy.
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