Geosaurine from Jurassic of Mexico + amniote hip joint mobility + lissamphibian and temnospondyl skull bone loss + tetrapod limb and digit identity evolution
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Ben Creisler
May 27, 2026, 1:15:28 PM (10 days ago) May 27
to DinosaurMa...@googlegroups.com
Ben Creisler
Recent tetrapod papers:
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Comment:
Kathryn Knight (2026)
Skin and muscle padding restrict reptile and mammal hips
Journal of Experimental Biology 229(10): jeb252709.
https://doi.org/10.1242/jeb.252709
https://journals.biologists.com/jeb/article/229/10/jeb252709/371716/Skin-and-muscle-padding-restrict-reptile-and
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Kim Julia Kean, Celeste M. Pérez-Ben, Marylène Danto & Nadia B. Fröbisch (2026)
What is driving the differential loss of skull bones throughout tetrapod evolution? Evidence from Temnospondyli
Proceedings of the Royal Society B: Biological Sciences 293(2071): 20253276 .
doi: https://doi.org/10.1098/rspb.2025.3276
https://royalsocietypublishing.org/rspb/article/293/2071/20253276/481898/What-is-driving-the-differential-loss-of-skull
Skull simplification describes the convergent loss of bones in the tetrapod skull over evolutionary time. Much of this trend remains elusive, in particular, the apparent difference in evolutionary conservation across the skull. While some bones (e.g. nasal) have been retained for over 400 million years, others (e.g. tabular) were repeatedly lost. The drivers of this preferential loss remain unknown. We explore whether the discrepancy in evolutionary conservation in the lissamphibian lineage was related to differences in evolvability of skull bones in their stem group, the temnospondyls. Linear morphometrics were applied to temnospondyl skull roof bones to quantify and compare the morphological disparity and evolutionary rates of bones that are lost and retained by lissamphibians. Analyses were conducted at inter- and intraspecific levels to capture the effects of development and natural selection on bone disparity. Bones lost in lissamphibians exhibited greater morphological disparity and evolutionary rates in temnospondyls than retained bones. This indicates that developmental bias may have promoted the retention of conserved bones. The higher disparity and evolutionary rates in bones absent in lissamphibians suggest that they were less constrained by development, potentially facilitating their loss in response to functional demands associated with buccal-pump breathing and eye retraction during feeding.
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Wen Kang, Ji-Feng Fei, Cong Liang, Günter Wagner & Qi Zhou (2026)
Evolution of limb and digit identity genes since the tetrapod ancestor
Nature Communications (advance online publication)
doi: https://doi.org/10.1038/s41467-026-73821-7
https://link.springer.com/article/10.1038/s41467-026-73821-7
Natural selection has sculpted tetrapod limbs and digits into a tremendous morphological diversity, but the underlying developmental mechanism remains unclear. This leads to an enduring debate concerning the identity of the three digits of bird wing. Here we use comparative digit transcriptomics across six tetrapod species to examine gene expression signatures of digit evolution. Here we show that the avian wing digits are homologous to reptilian forelimb digits 1,3,4. We find that birds uniquely increase fore-hindlimb transcriptome divergence during development, relaxing constraints and facilitating wing and foot digit specialization. We identify many limb- or digit- identity associated genes that have a biased expression between fore- or hind-limb, or toward specific digits. There are more limb and digit biased genes among the avian lineages than in other tetrapod lineages. Our work reveals ancient regulatory networks that maintain limb and digit molecular identity through persistent differential expression. We also show that this conserved network does not preclude independent digit evolution, especially when developmental constraints are reduced.
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Free pdf:
Jair Israel Barrientos-Lara & Jesús Alvarado-Ortega (2026)
A marine geosaurine crocodylomorph from the Kimmeridgian Sabinal Formation of Oaxaca, southern Mexico
Alcheringa (advance online publication)
doi: https://doi.org/10.1080/03115518.2026.2671704
https://www.tandfonline.com/doi/full/10.1080/03115518.2026.2671704
We report the first record of a geosaurine crocodylomorph from Kimmeridgian marine deposits of the Sabinal Formation at the Llano Yosobé locality in Oaxaca, southern Mexico. Although fragmentary, the fossil is probably part of either a dentary or maxilla preserving dental pits and three labiolingually compressed upright teeth. The presence of sinuous apicobasal ridges that reach the pseudoserrate cutting edges on the crown is consistent with Geosaurinae. However, the specimen is unique in possessing crown ridges that are evenly distributed over both labial and lingual surfaces. Excavations at the Llano Yosobé locality and its surroundings are ongoing, thus further discoveries of geosaurine remains are anticipated in the near future.
Jair Israel Barrientos-Lara & Jesús Alvarado-Ortega (2026)
A marine geosaurine crocodylomorph from the Kimmeridgian Sabinal Formation of Oaxaca, southern Mexico
Alcheringa (advance online publication)
doi: https://doi.org/10.1080/03115518.2026.2671704
https://www.tandfonline.com/doi/full/10.1080/03115518.2026.2671704
We report the first record of a geosaurine crocodylomorph from Kimmeridgian marine deposits of the Sabinal Formation at the Llano Yosobé locality in Oaxaca, southern Mexico. Although fragmentary, the fossil is probably part of either a dentary or maxilla preserving dental pits and three labiolingually compressed upright teeth. The presence of sinuous apicobasal ridges that reach the pseudoserrate cutting edges on the crown is consistent with Geosaurinae. However, the specimen is unique in possessing crown ridges that are evenly distributed over both labial and lingual surfaces. Excavations at the Llano Yosobé locality and its surroundings are ongoing, thus further discoveries of geosaurine remains are anticipated in the near future.
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Mark A. Wright & Stephanie E. Pierce (2026)
Soft tissue constraints on hip joint mobility in a sprawling and parasagittal amniote
Journal of Experimental Biology 229(10): jeb251911.
https://doi.org/10.1242/jeb.251911
https://journals.biologists.com/jeb/article-abstract/229/10/jeb251911/371717/Soft-tissue-constraints-on-hip-joint-mobility-in-a
Soft tissues, in addition to bones, are known to constrain joint mobility, yet the amount and type of influence remain underexplored. To investigate this further, we used XROMM to quantify ex vivo hip joint mobility during sequential removal of soft tissue layers (e.g. integument, extrinsic muscles, intrinsic muscles) in two amniotes that span a postural continuum: the sprawling tegu lizard (Salvator merianae) and the parasagittal Virginia opossum (Didelphis virginiana). We then compared ex vivo hip joint mobility spaces with in vivo joint excursions during steady-state walking recorded with bi-planar fluoroscopes. Our results demonstrate that integument passively restricts hip joint mobility in the tegu but not the opossum, while extrinsic muscles restrict mobility in the opossum but not the tegu due to the relatively bulky thighs of mammals. We further show that the tegu has greater ex vivo mobility than the opossum across tissue layers and during in vivo walking despite the classic ball-and-socket hip joint structure of mammals – a morphology traditionally interpreted as highly mobile. Finally, comparing in vivo hip joint excursion during walking with ex vivo mobility in both animals showed that soft tissues restrict stance phase excursions while swing phase movements approach the edge of viable ex vivo pose space. Collectively, our experimental findings provide novel insights and expand our understanding of the influence of soft tissues on joint mobility in vivo, ex vivo and in animals with unique postures, helping to aid future reconstructions of joint function and movement in extinct vertebrates.
Soft tissue constraints on hip joint mobility in a sprawling and parasagittal amniote
Journal of Experimental Biology 229(10): jeb251911.
https://doi.org/10.1242/jeb.251911
https://journals.biologists.com/jeb/article-abstract/229/10/jeb251911/371717/Soft-tissue-constraints-on-hip-joint-mobility-in-a
Soft tissues, in addition to bones, are known to constrain joint mobility, yet the amount and type of influence remain underexplored. To investigate this further, we used XROMM to quantify ex vivo hip joint mobility during sequential removal of soft tissue layers (e.g. integument, extrinsic muscles, intrinsic muscles) in two amniotes that span a postural continuum: the sprawling tegu lizard (Salvator merianae) and the parasagittal Virginia opossum (Didelphis virginiana). We then compared ex vivo hip joint mobility spaces with in vivo joint excursions during steady-state walking recorded with bi-planar fluoroscopes. Our results demonstrate that integument passively restricts hip joint mobility in the tegu but not the opossum, while extrinsic muscles restrict mobility in the opossum but not the tegu due to the relatively bulky thighs of mammals. We further show that the tegu has greater ex vivo mobility than the opossum across tissue layers and during in vivo walking despite the classic ball-and-socket hip joint structure of mammals – a morphology traditionally interpreted as highly mobile. Finally, comparing in vivo hip joint excursion during walking with ex vivo mobility in both animals showed that soft tissues restrict stance phase excursions while swing phase movements approach the edge of viable ex vivo pose space. Collectively, our experimental findings provide novel insights and expand our understanding of the influence of soft tissues on joint mobility in vivo, ex vivo and in animals with unique postures, helping to aid future reconstructions of joint function and movement in extinct vertebrates.
***
Comment:
Kathryn Knight (2026)
Skin and muscle padding restrict reptile and mammal hips
Journal of Experimental Biology 229(10): jeb252709.
https://doi.org/10.1242/jeb.252709
https://journals.biologists.com/jeb/article/229/10/jeb252709/371716/Skin-and-muscle-padding-restrict-reptile-and
====
====
Free pdf:
Kim Julia Kean, Celeste M. Pérez-Ben, Marylène Danto & Nadia B. Fröbisch (2026)
What is driving the differential loss of skull bones throughout tetrapod evolution? Evidence from Temnospondyli
Proceedings of the Royal Society B: Biological Sciences 293(2071): 20253276 .
doi: https://doi.org/10.1098/rspb.2025.3276
https://royalsocietypublishing.org/rspb/article/293/2071/20253276/481898/What-is-driving-the-differential-loss-of-skull
Skull simplification describes the convergent loss of bones in the tetrapod skull over evolutionary time. Much of this trend remains elusive, in particular, the apparent difference in evolutionary conservation across the skull. While some bones (e.g. nasal) have been retained for over 400 million years, others (e.g. tabular) were repeatedly lost. The drivers of this preferential loss remain unknown. We explore whether the discrepancy in evolutionary conservation in the lissamphibian lineage was related to differences in evolvability of skull bones in their stem group, the temnospondyls. Linear morphometrics were applied to temnospondyl skull roof bones to quantify and compare the morphological disparity and evolutionary rates of bones that are lost and retained by lissamphibians. Analyses were conducted at inter- and intraspecific levels to capture the effects of development and natural selection on bone disparity. Bones lost in lissamphibians exhibited greater morphological disparity and evolutionary rates in temnospondyls than retained bones. This indicates that developmental bias may have promoted the retention of conserved bones. The higher disparity and evolutionary rates in bones absent in lissamphibians suggest that they were less constrained by development, potentially facilitating their loss in response to functional demands associated with buccal-pump breathing and eye retraction during feeding.
=====
Free pdf:
Wen Kang, Ji-Feng Fei, Cong Liang, Günter Wagner & Qi Zhou (2026)
Evolution of limb and digit identity genes since the tetrapod ancestor
Nature Communications (advance online publication)
doi: https://doi.org/10.1038/s41467-026-73821-7
https://link.springer.com/article/10.1038/s41467-026-73821-7
Natural selection has sculpted tetrapod limbs and digits into a tremendous morphological diversity, but the underlying developmental mechanism remains unclear. This leads to an enduring debate concerning the identity of the three digits of bird wing. Here we use comparative digit transcriptomics across six tetrapod species to examine gene expression signatures of digit evolution. Here we show that the avian wing digits are homologous to reptilian forelimb digits 1,3,4. We find that birds uniquely increase fore-hindlimb transcriptome divergence during development, relaxing constraints and facilitating wing and foot digit specialization. We identify many limb- or digit- identity associated genes that have a biased expression between fore- or hind-limb, or toward specific digits. There are more limb and digit biased genes among the avian lineages than in other tetrapod lineages. Our work reveals ancient regulatory networks that maintain limb and digit molecular identity through persistent differential expression. We also show that this conserved network does not preclude independent digit evolution, especially when developmental constraints are reduced.
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