Mammaliamorph jaw joint convergent evolution + squamate fossil record + tetrapod ichnofauna from Permian of Brazil
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Ben Creisler
Sep 24, 2025, 1:20:22 PM (5 days ago) Sep 24
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Ben Creisler
Recent papers:
Fangyuan Mao, Shan Jiang, Jun Liu, Jicheng Ren, Yong Ye, Yu Liu, Xin Shen, Tao Wang, Guofu Wang, Ping Wang, Juan Chen & Jin Meng (2025)
Convergent evolution of diverse jaw joints in mammaliamorphs
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-025-09572-0
https://www.nature.com/articles/s41586-025-09572-0
The evolution of a single-dentary-boned lower jaw and its secondary craniomandibular articulation between the dentary condyle and the squamosal glenoid has been regarded as a pivotal vertebrate innovation and defining mammalian trait. Here we report two mammaliamorphs with novel shapes of secondary jaw joint, offering insight into the evolution of the mammalian jaw. The first, Polistodon, a Middle Jurassic herbivorous tritylodontid with a relatively large body size and a lifestyle that is likely to have been fossorial, uniquely evolved a dentary–jugal articulation. The second, an Early Jurassic morganucodontan, exhibits a dentary–squamosal joint that lacks a bulbous condyle, supporting the hypothesis that the mammalian dentary condyle was formed by expansion of the lateral ridge of the dentary. These diverse joints reflect repeated evolutionary experimentation in advanced cynodonts, in which secondary jaw joints arose independently, and in which the load-bearing dentary–squamosal joint is a synapomorphy of mammaliaforms. Although body miniaturization might have driven this transformation, our findings indicate that other factors were involved, such as jaw-muscle reorganization, feeding ecology and masticatory behaviour. The ecomorphological diversity of these taxa suggest that phenotypic plasticity and environmentally induced morphological changes could have shaped jaw-joint evolution, emphasizing how ecological pressures and developmental flexibility guided the diversification of jaw structures in mammalian ancestors.
Convergent evolution of diverse jaw joints in mammaliamorphs
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-025-09572-0
https://www.nature.com/articles/s41586-025-09572-0
The evolution of a single-dentary-boned lower jaw and its secondary craniomandibular articulation between the dentary condyle and the squamosal glenoid has been regarded as a pivotal vertebrate innovation and defining mammalian trait. Here we report two mammaliamorphs with novel shapes of secondary jaw joint, offering insight into the evolution of the mammalian jaw. The first, Polistodon, a Middle Jurassic herbivorous tritylodontid with a relatively large body size and a lifestyle that is likely to have been fossorial, uniquely evolved a dentary–jugal articulation. The second, an Early Jurassic morganucodontan, exhibits a dentary–squamosal joint that lacks a bulbous condyle, supporting the hypothesis that the mammalian dentary condyle was formed by expansion of the lateral ridge of the dentary. These diverse joints reflect repeated evolutionary experimentation in advanced cynodonts, in which secondary jaw joints arose independently, and in which the load-bearing dentary–squamosal joint is a synapomorphy of mammaliaforms. Although body miniaturization might have driven this transformation, our findings indicate that other factors were involved, such as jaw-muscle reorganization, feeding ecology and masticatory behaviour. The ecomorphological diversity of these taxa suggest that phenotypic plasticity and environmentally induced morphological changes could have shaped jaw-joint evolution, emphasizing how ecological pressures and developmental flexibility guided the diversification of jaw structures in mammalian ancestors.
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Elsa Panciroli (2025)
Jazzy jaw joints: evolutionary fine-tuning reveals unexpected bone connections in ancient predecessors of mammals
The evolution of the jaw helped mammals to thrive. Fossil discoveries shed light on the diverse evolutionary journeys taken by joints between the skull and lower jaw.
Nature (advance online publication)
doi: https://doi.org/10.1038/d41586-025-02823-0
https://www.nature.com/articles/d41586-025-02823-0
The arrangement of the bones that form the joint (the articulation) between the lower jaw and the skull is a key hallmark of vertebrates. Their configuration has long been used to draw a line in the fossil record between what is and is not considered a mammal. Writing in Nature, Mao et al. describe the skulls of two ancient predecessors of mammals that have previously unknown types of jaw joint. These discoveries force us to re-evaluate the evolutionary path of jaw-joint formation, and suggest surprising flexibility in how mammalian ancestors adapted to changing ecological pressures.
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News:
High-resolution fossil scans reveal four-step process of mammalian jaw joint evolution
https://phys.org/news/2025-09-high-resolution-fossil-scans-reveal.html
https://phys.org/news/2025-09-high-resolution-fossil-scans-reveal.html
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Free pdf:
C. Henrik Woolley, David J. Bottjer & Nathan D Smith (2025)
Taphonomic megabiases constrain phylogenetic information in the squamate fossil record
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2025.10060
https://www.cambridge.org/core/journals/paleobiology/article/taphonomic-megabiases-constrain-phylogenetic-information-in-the-squamate-fossil-record/8632018C57CB8AE1E4C294DC804C2389
Fossil data are subject to inherent biological, geologic, and anthropogenic filters that can distort our interpretations of ancient life and environments. The inevitable presence of incomplete fossils thus requires a holistic assessment of how to navigate the downstream effects of bias on our ability to accurately reconstruct aspects of biology in deep time. In particular, we must assess how biases affect our capacity to infer evolutionary relationships, which are essential to analyses of diversification, paleobiogeography, and biostratigraphy in Earth history. In this study, we use an established completeness metric to quantify the effects of taphonomic filters on the amount of phylogenetic information available in the fossil record of 795 extinct squamate (e.g., lizards, snakes, amphisbaenians, and mosasaurs) species spanning 242 Myr of geologic time. This study found no meaningful relationship between spatiotemporal sampling intensity and fossil record completeness. Instead, major differences in squamate fossil record completeness stem from a combination of anatomy/body size and affinities of different squamate groups to specific lithologies and depositional environments. These results reveal that naturally occurring processes create structural megabiases that filter anatomical and phylogenetic data in the squamate fossil record, while anthropogenic processes play a secondary role.
Non-technical Summary
In reconstructing biodiversity patterns from Earth’s past, it is crucial to understand the quality of the inherently incomplete fossil data that results from exposure to thousands to millions of years of geologic processes, as well as human-based sampling biases. One of the most straightforward ways to broadly understand the quality of the fossil record is to implement “completeness metrics” to ascertain the amount and availability of skeletal and evolutionary information. In this study, we use the Character Completeness Metric (CCM) to measure the percentage of phylogenetic characters that can be scored for a given fossil species, based on the preserved elements of a species’ anatomy. We use the CCM to quantify the nature of bias in the >242 million year fossil record of squamates (e.g., lizards, snakes, amphisbaenians, mosasaurs, and their relatives). We use published descriptions of 795 fossil squamate species spanning 242 million years of the group’s evolutionary history. We find that natural processes, such as the animal’s anatomy/body size and affinities to specific environments (e.g., marine, desert sand dunes, rivers, and lakes) are more reliable predictors of squamate fossil record completeness than processes related to sampling intensity among workers. These results illustrate the nuances of fossil record completeness specific to individual lineages and add to growing evidence that heightened research interest and sample size does not always produce a more complete fossil record.
C. Henrik Woolley, David J. Bottjer & Nathan D Smith (2025)
Taphonomic megabiases constrain phylogenetic information in the squamate fossil record
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2025.10060
https://www.cambridge.org/core/journals/paleobiology/article/taphonomic-megabiases-constrain-phylogenetic-information-in-the-squamate-fossil-record/8632018C57CB8AE1E4C294DC804C2389
Fossil data are subject to inherent biological, geologic, and anthropogenic filters that can distort our interpretations of ancient life and environments. The inevitable presence of incomplete fossils thus requires a holistic assessment of how to navigate the downstream effects of bias on our ability to accurately reconstruct aspects of biology in deep time. In particular, we must assess how biases affect our capacity to infer evolutionary relationships, which are essential to analyses of diversification, paleobiogeography, and biostratigraphy in Earth history. In this study, we use an established completeness metric to quantify the effects of taphonomic filters on the amount of phylogenetic information available in the fossil record of 795 extinct squamate (e.g., lizards, snakes, amphisbaenians, and mosasaurs) species spanning 242 Myr of geologic time. This study found no meaningful relationship between spatiotemporal sampling intensity and fossil record completeness. Instead, major differences in squamate fossil record completeness stem from a combination of anatomy/body size and affinities of different squamate groups to specific lithologies and depositional environments. These results reveal that naturally occurring processes create structural megabiases that filter anatomical and phylogenetic data in the squamate fossil record, while anthropogenic processes play a secondary role.
Non-technical Summary
In reconstructing biodiversity patterns from Earth’s past, it is crucial to understand the quality of the inherently incomplete fossil data that results from exposure to thousands to millions of years of geologic processes, as well as human-based sampling biases. One of the most straightforward ways to broadly understand the quality of the fossil record is to implement “completeness metrics” to ascertain the amount and availability of skeletal and evolutionary information. In this study, we use the Character Completeness Metric (CCM) to measure the percentage of phylogenetic characters that can be scored for a given fossil species, based on the preserved elements of a species’ anatomy. We use the CCM to quantify the nature of bias in the >242 million year fossil record of squamates (e.g., lizards, snakes, amphisbaenians, mosasaurs, and their relatives). We use published descriptions of 795 fossil squamate species spanning 242 million years of the group’s evolutionary history. We find that natural processes, such as the animal’s anatomy/body size and affinities to specific environments (e.g., marine, desert sand dunes, rivers, and lakes) are more reliable predictors of squamate fossil record completeness than processes related to sampling intensity among workers. These results illustrate the nuances of fossil record completeness specific to individual lineages and add to growing evidence that heightened research interest and sample size does not always produce a more complete fossil record.
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Murilo Andrade-Silva & Heitor Francischini (2025)
Revisiting the tetrapod ichnofauna of the Rio do Rasto Formation (middle-upper Permian), southern Brazil
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2557942
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2557942
Tetrapod footprints are abundant and morphologically diverse throughout the Permian. However, the morphological similarities among ichnogenera often lead to misidentification or taxonomic confusion. In this study, we reanalysed eight slabs from the Rio do Rasto Formation (upper Permian) of southern Brazil, previously attributed to Dicynodontipus penugnu, Procolophonichnium isp. and Rhynchosauroides gangresci. Through detailed examination of dactyl morphology, gradial structure, digit proportions, and the relative position of digit V, we reinterpret these footprints as belonging to the ichnospecies Batrachichnus salamandroides and Procolophonichnium nopcsai. Additionally, a newly analysed specimen is described here for the first time and assigned to the ichnospecies B. salamandroides. These findings extend the temporal range of these ichnogenera into the Wuchiapingian, providing new insights into the palaeoecology and evolutionary history of late Permian tetrapods.
urn:lsid:zoobank.org:pub:230854F1-B0BC-4713-B77D-1C5219EC7656
Ben Creisler
Sep 24, 2025, 1:34:21 PM (5 days ago) Sep 24
to DinosaurMa...@googlegroups.com
The first paper names a new morganucodontan taxon:
Camurocondylus lufengensis gen. et sp. nov.
Also:
Chinese scientists uncover new evidence, hypotheses on mammalian jaw joint evolution from museum-hold specimens
Camurocondylus lufengensis gen. et sp. nov.
Also:
Chinese scientists uncover new evidence, hypotheses on mammalian jaw joint evolution from museum-hold specimens
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