Rhynchosaur ankylothecodont tooth attachment + Cuban ichthyosaur with lost holotype
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Ben Creisler
Aug 28, 2025, 11:57:06 PM (10 days ago) Aug 28
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Ben Creisler
Recent papers:
The study of the connection between the teeth and the jaw is important for understanding the palaeobiology of vertebrates, but inconsistent terminology and incomplete sampling have made it difficult to assess the evolutionary significance of some of the related characters. Among archosauromorphs, tooth attachment in dinosaurs and crocodylians is nearly identical to that of mammals in featuring a ligamentous connection (gomphosis), whereas closely related forms appear to have teeth fused to the jaws (ankylosis), as in most other amniotes. Hence, studying tooth attachment of stem-archosaurs is pivotal to characterize the main shifts in tooth attachment seen in the lineage. Here, we analyze the tooth attachment of rhynchosaurs — a group of quadrupedal herbivorous archosauromorphs that played a key role as primary consumers in many Triassic communities. Their dentition consists of multiple rows of marginal teeth with posterolingual addition of teeth during growth, but their tooth attachment has not been documented in a modern context. Histological data from three rhynchosaur specimens from the Middle Triassic Manda Beds of Tanzania show that, although ankylosed, rhynchosaur teeth are surrounded by an extensive network of Sharpey’s fibers, layers of cementum, and well-defined zones of alveolar bone. What has been previously described as “spongy bone of attachment” in fact encompasses the same attachment tissues present in mammals, dinosaurs, and crocodylians, albeit completely mineralized in mature teeth. Analysis of different stages of tooth development shows that ankylosis occurs by the growth of alveolar bone towards the cellular cementum, which eventually mineralizes the soft ligament. This suggests that the tissues conflated as “bone of attachment”—alveolar bone, periodontal ligament, and cellular cementum—are homologous across Archosauromorpha. Our data add to a growing body of evidence that heterochronic changes to the timing and extents of mineralization, not convergent evolution to mammal-like attachment tissues, led to the independent evolution of gomphosis across many amniote lineages, including archosauromorphs.
Graphical Abstract
Dental evolution is a major topic in vertebrate palaeontology and provides key insights into the evolutionary history of several amniote clades. This study investigates rhynchosaur ankylothecodonty within the broader evolutionary context of Archosauromorpha. Our results show that rhynchosaur dentition comprises the plesiomorphic amniote tissues — alveolar bone, cellular cementum, and the mineralized periodontal ligament — challenging assumptions about the so-called “bone of attachment.” Within this framework, rhynchosaurs exhibit rapid ankylosis, adding to a growing body of evidence that heterochronic shifts in mineralization timing led to the evolution of gomphosis across many amniote clades, including mammals, dinosaurs, and crocodylians.
Free pdf:
Gabriel Mestriner, Gregory F. Funston, Sterling J. Nesbitt, Júlio C. A. Marsola, David C. Evans, Christian A. Sidor, Max C. Langer, Aaron R. H. LeBlanc
The histology of rhynchosaur (Diapsida, Archosauromorpha) ankylothecodonty
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70037
https://onlinelibrary.wiley.com/doi/10.1111/joa.70037
Gabriel Mestriner, Gregory F. Funston, Sterling J. Nesbitt, Júlio C. A. Marsola, David C. Evans, Christian A. Sidor, Max C. Langer, Aaron R. H. LeBlanc
The histology of rhynchosaur (Diapsida, Archosauromorpha) ankylothecodonty
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70037
https://onlinelibrary.wiley.com/doi/10.1111/joa.70037
The study of the connection between the teeth and the jaw is important for understanding the palaeobiology of vertebrates, but inconsistent terminology and incomplete sampling have made it difficult to assess the evolutionary significance of some of the related characters. Among archosauromorphs, tooth attachment in dinosaurs and crocodylians is nearly identical to that of mammals in featuring a ligamentous connection (gomphosis), whereas closely related forms appear to have teeth fused to the jaws (ankylosis), as in most other amniotes. Hence, studying tooth attachment of stem-archosaurs is pivotal to characterize the main shifts in tooth attachment seen in the lineage. Here, we analyze the tooth attachment of rhynchosaurs — a group of quadrupedal herbivorous archosauromorphs that played a key role as primary consumers in many Triassic communities. Their dentition consists of multiple rows of marginal teeth with posterolingual addition of teeth during growth, but their tooth attachment has not been documented in a modern context. Histological data from three rhynchosaur specimens from the Middle Triassic Manda Beds of Tanzania show that, although ankylosed, rhynchosaur teeth are surrounded by an extensive network of Sharpey’s fibers, layers of cementum, and well-defined zones of alveolar bone. What has been previously described as “spongy bone of attachment” in fact encompasses the same attachment tissues present in mammals, dinosaurs, and crocodylians, albeit completely mineralized in mature teeth. Analysis of different stages of tooth development shows that ankylosis occurs by the growth of alveolar bone towards the cellular cementum, which eventually mineralizes the soft ligament. This suggests that the tissues conflated as “bone of attachment”—alveolar bone, periodontal ligament, and cellular cementum—are homologous across Archosauromorpha. Our data add to a growing body of evidence that heterochronic changes to the timing and extents of mineralization, not convergent evolution to mammal-like attachment tissues, led to the independent evolution of gomphosis across many amniote lineages, including archosauromorphs.
Graphical Abstract
Dental evolution is a major topic in vertebrate palaeontology and provides key insights into the evolutionary history of several amniote clades. This study investigates rhynchosaur ankylothecodonty within the broader evolutionary context of Archosauromorpha. Our results show that rhynchosaur dentition comprises the plesiomorphic amniote tissues — alveolar bone, cellular cementum, and the mineralized periodontal ligament — challenging assumptions about the so-called “bone of attachment.” Within this framework, rhynchosaurs exhibit rapid ankylosis, adding to a growing body of evidence that heterochronic shifts in mineralization timing led to the evolution of gomphosis across many amniote clades, including mammals, dinosaurs, and crocodylians.
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Yasmani Ceballos Izquierdo, Johanset Orihuela, Mark T. Young, Sven Sachs, Ernesto Aranda & Lázaro W. Viñola-López (2025)
What is ‘Ichthyosaurus’ torrei? Remarks on the lost holotype of a Cuban marine reptile
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2541816
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2541816
The Jagua Formation (Oxfordian, Late Jurassic) of western Cuba preserves a diverse marine vertebrate assemblage, including ichthyosaurs and metriorhynchid crocodylomorphs. Among these, the taxonomic placement of ‘Ichthyosaurus’ torrei remains unresolved. The holotype and only specimen (MNHNCu P 3001), a fragmentary skull and mandible, was initially assigned to Ichthyosauridae based on its conical dentition but has since been reinterpreted as a metriorhynchid or indeterminate Jurassic reptile. The specimen, formerly housed at the Museo Nacional de Historia Natural de Cuba (MNHNCu), is now lost, limiting reassessment to photographs, CT scans, and original descriptions. Here, we redescribe the specimen based on the available data and provide the first comprehensive reassessment since its loss. MNHNCu P 3001 is an incomplete cranium with a sub-circular orbit, anteroposteriorly elongated external naris, and conical, unserrated teeth. The preserved morphology has features not seen in metriorhynchids such as paired frontals, extreme elongation of the premaxilla and external nares retracted close to the orbits. Similarly, plesiosaurian diagnostic characters are absent. While its fragmentary nature precludes definitive classification, available evidence supports an ichthyosaurian affinity. This study underscores the significance of the Jagua Formation in revealing the diversity of Jurassic marine reptiles in the Proto-Caribbean region.
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What is ‘Ichthyosaurus’ torrei? Remarks on the lost holotype of a Cuban marine reptile
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2541816
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2541816
The Jagua Formation (Oxfordian, Late Jurassic) of western Cuba preserves a diverse marine vertebrate assemblage, including ichthyosaurs and metriorhynchid crocodylomorphs. Among these, the taxonomic placement of ‘Ichthyosaurus’ torrei remains unresolved. The holotype and only specimen (MNHNCu P 3001), a fragmentary skull and mandible, was initially assigned to Ichthyosauridae based on its conical dentition but has since been reinterpreted as a metriorhynchid or indeterminate Jurassic reptile. The specimen, formerly housed at the Museo Nacional de Historia Natural de Cuba (MNHNCu), is now lost, limiting reassessment to photographs, CT scans, and original descriptions. Here, we redescribe the specimen based on the available data and provide the first comprehensive reassessment since its loss. MNHNCu P 3001 is an incomplete cranium with a sub-circular orbit, anteroposteriorly elongated external naris, and conical, unserrated teeth. The preserved morphology has features not seen in metriorhynchids such as paired frontals, extreme elongation of the premaxilla and external nares retracted close to the orbits. Similarly, plesiosaurian diagnostic characters are absent. While its fragmentary nature precludes definitive classification, available evidence supports an ichthyosaurian affinity. This study underscores the significance of the Jagua Formation in revealing the diversity of Jurassic marine reptiles in the Proto-Caribbean region.
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