Riojasuchus rostral neurovascular anatomy + Cryptochersis & Ypomonetikochelys, new Triassic turtles from Greenland + Sphenodon axial skeleton
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Ben Creisler
Apr 1, 2026, 11:11:02 AM (2 days ago) Apr 1
to DinosaurMa...@googlegroups.com
Ben Creisler
Some new and recent reptile papers:
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Turtles (Testudinata) are a common faunal component throughout most of the Mesozoic and Cenozoic. Particularly, one of their Triassic genera, Proganochelys, was considered exceptionally successful and widespread, inhabiting nearly the whole of northern Pangaea. However, only recently the understanding of the anatomy and taxonomy of Triassic turtles improved, allowing determination of new diagnostic characters and a more granular approach to their taxonomy, revealing a more nuanced distribution than was previously assumed. Herein, two new genera and species of Triassic turtles are described from the Late Triassic (Norian) Fleming Fjord Formation of Greenland. The new taxa represent two of the three known Triassic turtle clades: Proterochersidae and Proganochelyidae. The proterochersid, Cryptochersis paraxene gen. et sp. nov., presents a unique form of the posterior plastral lobe. The proganochelyid, Ypomonetikochelys euryaspis gen. et sp. nov., is now the second known valid representative of its clade. Its generic distinctiveness reveals the solely central Pangaean (modern-day Central European) distribution of the genus Proganochelys. The fossil record indicates that soon after their appearance, the turtles achieved a considerable taxonomic diversity and a widespread distribution, covering most of the northern and a part of the southern hemisphere.
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Convergent evolution can undermine parsimony as a criterion for choosing among phylogenetic hypotheses, resulting in a challenge to find consensus among conflicting trees. This challenge is exemplified in the studies of sea turtle (Pan-Chelonioidea) evolution. Despite the wide interest in this iconic clade, rigorous analyses of character acquisition are currently limited by poorly resolved, largely parsimony-based phylogenies. In particular, there is uncertainty regarding the placement of the extinct family Protostegidae, which has been recovered in several different parts of the tree and even outside Pan-Chelonioidea as a separate radiation of marine turtles. The relationships among the stem of Cheloniidae are also far from a consensus, despite it having a relatively good fossil record. Here we investigate the evolution of sea turtles using a Bayesian tip-dating approach, a technique not previously applied to this group. We also conduct a biogeographic analysis using DEC and DECJ models. We find Protostegidae to be sister to the rest of Pan-Chelonioidea, implying convergent evolution of the sea turtle flipper and other marine adaptations. We find that Chelonioidea probably originated in the North Atlantic, and that the now global distribution of most sea turtle species suggests that the pelagic life phase of extant species is unique to crown Cheloniidae.
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Victor Beccari, Marc E H Jones, Andrea Villa, Roberta Martino, Sophie Regnault, Frank Glaw & Oliver W M Rauhut (2026)
The axial skeleton of the tuatara (Rhynchocephalia: Sphenodon): insights on intraspecific variability, ontogeny, sexual dimorphism, and remarks on fossil taxa
Zoological Journal of the Linnean Society 206(4) zlaf135
doi: https://doi.org/10.1093/zoolinnean/zlaf135
https://academic.oup.com/zoolinnean/article/206/4/zlaf135/8570147
As the sole living rhynchocephalian, the tuatara (Sphenodon punctatus) provides important comparative information for fossil rhynchocephalians and lepidosaurs in general regarding expected intraspecific variability, ontogeny, and sexual dimorphism. The axial skeleton of Sphenodon punctatus is described here in detail, using Computed Tomography (CT)-scans and a comprehensive sample (N = 33) of different ontogenetic stages and sexes. The new description adds to already existing literature, and confirms some consistent morphological characters, such as number of vertebrae, position of accessory processes, and ossification patterns. We conducted 3D geometric morphometrics analyses to better understand regionalization of the axial skeleton, ontogenetic changes, and sexual dimorphism in Sphenodon. The morphology of presacral vertebrae is influenced by size and shows negative allometry, with increasing relative height of the neural spine, but decreasing relative vertebral width and length in larger individuals. We compare the morphology and ontogenetic implications of Sphenodon with Mesozoic fossil relatives. Some taxa, especially those from the Jurassic of Europe, show substantial differences in number, proportions, and morphology of vertebrae, including shifts in ossification timing, loss of vertebral intercentra, and changes in rib morphology. We highlight osteological features, such as ossification timing and morphology, that may correlate with taxonomy, systematics, and ecomorphology of Mesozoic rhynchocephalians.
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Karen Ulloa-Guaiquin, María Belen von Baczko, Julia Brenda Desojo & Ariana Paulina-Carabajal (2026)
Complex rostral neurovascular anatomy of Riojasuchus tenuisceps (Archosauria: Pseudosuchia) and implications for trophic hypotheses in ornithosuchids
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.70186
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70186
Ornithosuchids are distinctive pseudosuchian archosaurs from the Late Triassic whose feeding habits remain debated. Previous paleoneurological and histological studies provided limited information about their paleobiology. To address this, we analyzed the craniofacial neurovascular anatomy of Riojasuchus tenuisceps to infer its functional and ecological implications and to reassess hypotheses about ornithosuchid feeding behavior. The holotype and a referred specimen were studied. The snout of PVL 3828 was analyzed using micro-computed tomography, enabling digital reconstruction of the rostral neurovascular system. We applied a quantitative framework, including ordinary least squares regressions and principal component analysis, to compare neurovascular patterns across Triassic pseudosuchians (e.g., Erpetosuchidae, Gracilisuchidae, and Loricata). The premaxilla exhibits a complex internal anatomy, with neurovascular canals connecting to external foramina. Our results reveal a foramen density significantly higher than the group's baseline, a configuration that differs from other pseudosuchians and resembles the mechanosensory systems of extant crocodilians and some birds. These findings indicate that R tenuisceps may have used its snout for tactile prey detection, protection from mechanical forces during feeding, or to maintain a high vascular supply. Combined with biomechanical and osteological data, this supports a wading-foraging behavior rather than scavenging or active terrestrial hunting, highlighting a sophisticated resource partitioning and an underestimated ecological diversity among Triassic pseudosuchians.
Karen Ulloa-Guaiquin, María Belen von Baczko, Julia Brenda Desojo & Ariana Paulina-Carabajal (2026)
Complex rostral neurovascular anatomy of Riojasuchus tenuisceps (Archosauria: Pseudosuchia) and implications for trophic hypotheses in ornithosuchids
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.70186
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70186
Ornithosuchids are distinctive pseudosuchian archosaurs from the Late Triassic whose feeding habits remain debated. Previous paleoneurological and histological studies provided limited information about their paleobiology. To address this, we analyzed the craniofacial neurovascular anatomy of Riojasuchus tenuisceps to infer its functional and ecological implications and to reassess hypotheses about ornithosuchid feeding behavior. The holotype and a referred specimen were studied. The snout of PVL 3828 was analyzed using micro-computed tomography, enabling digital reconstruction of the rostral neurovascular system. We applied a quantitative framework, including ordinary least squares regressions and principal component analysis, to compare neurovascular patterns across Triassic pseudosuchians (e.g., Erpetosuchidae, Gracilisuchidae, and Loricata). The premaxilla exhibits a complex internal anatomy, with neurovascular canals connecting to external foramina. Our results reveal a foramen density significantly higher than the group's baseline, a configuration that differs from other pseudosuchians and resembles the mechanosensory systems of extant crocodilians and some birds. These findings indicate that R tenuisceps may have used its snout for tactile prey detection, protection from mechanical forces during feeding, or to maintain a high vascular supply. Combined with biomechanical and osteological data, this supports a wading-foraging behavior rather than scavenging or active terrestrial hunting, highlighting a sophisticated resource partitioning and an underestimated ecological diversity among Triassic pseudosuchians.
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Cryptochersis paraxene gen. et sp. nov.
Ypomonetikochelys euryaspis gen. et sp. nov.
Tomasz Szczygielski & Dawid Dróżdż (2026)
Triassic turtles (Testudinata: Proterochersidae and Proganochelyidae) of Greenland
Zoological Journal of the Linnean Society 206(3): zlag011,
doi: https://doi.org/10.1093/zoolinnean/zlag011
https://academic.oup.com/zoolinnean/article-abstract/206/3/zlag011/8544869
Ypomonetikochelys euryaspis gen. et sp. nov.
Tomasz Szczygielski & Dawid Dróżdż (2026)
Triassic turtles (Testudinata: Proterochersidae and Proganochelyidae) of Greenland
Zoological Journal of the Linnean Society 206(3): zlag011,
doi: https://doi.org/10.1093/zoolinnean/zlag011
https://academic.oup.com/zoolinnean/article-abstract/206/3/zlag011/8544869
Turtles (Testudinata) are a common faunal component throughout most of the Mesozoic and Cenozoic. Particularly, one of their Triassic genera, Proganochelys, was considered exceptionally successful and widespread, inhabiting nearly the whole of northern Pangaea. However, only recently the understanding of the anatomy and taxonomy of Triassic turtles improved, allowing determination of new diagnostic characters and a more granular approach to their taxonomy, revealing a more nuanced distribution than was previously assumed. Herein, two new genera and species of Triassic turtles are described from the Late Triassic (Norian) Fleming Fjord Formation of Greenland. The new taxa represent two of the three known Triassic turtle clades: Proterochersidae and Proganochelyidae. The proterochersid, Cryptochersis paraxene gen. et sp. nov., presents a unique form of the posterior plastral lobe. The proganochelyid, Ypomonetikochelys euryaspis gen. et sp. nov., is now the second known valid representative of its clade. Its generic distinctiveness reveals the solely central Pangaean (modern-day Central European) distribution of the genus Proganochelys. The fossil record indicates that soon after their appearance, the turtles achieved a considerable taxonomic diversity and a widespread distribution, covering most of the northern and a part of the southern hemisphere.
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Ray M Chatterji, Mark N Hutchinson & Marc E H Jones (2026)
Bayesian tip-dating and biogeographic approaches reveal multiple marine transitions in Pan-Chelonioidea and a North Atlantic origin for modern sea turtles (Chelonioidea)Get accessArrow
Zoological Journal of the Linnean Society 206(4): zlag024
doi: https://doi.org/10.1093/zoolinnean/zlag024
https://academic.oup.com/zoolinnean/article-abstract/206/4/zlag024/8570146
Bayesian tip-dating and biogeographic approaches reveal multiple marine transitions in Pan-Chelonioidea and a North Atlantic origin for modern sea turtles (Chelonioidea)Get accessArrow
Zoological Journal of the Linnean Society 206(4): zlag024
doi: https://doi.org/10.1093/zoolinnean/zlag024
https://academic.oup.com/zoolinnean/article-abstract/206/4/zlag024/8570146
Convergent evolution can undermine parsimony as a criterion for choosing among phylogenetic hypotheses, resulting in a challenge to find consensus among conflicting trees. This challenge is exemplified in the studies of sea turtle (Pan-Chelonioidea) evolution. Despite the wide interest in this iconic clade, rigorous analyses of character acquisition are currently limited by poorly resolved, largely parsimony-based phylogenies. In particular, there is uncertainty regarding the placement of the extinct family Protostegidae, which has been recovered in several different parts of the tree and even outside Pan-Chelonioidea as a separate radiation of marine turtles. The relationships among the stem of Cheloniidae are also far from a consensus, despite it having a relatively good fossil record. Here we investigate the evolution of sea turtles using a Bayesian tip-dating approach, a technique not previously applied to this group. We also conduct a biogeographic analysis using DEC and DECJ models. We find Protostegidae to be sister to the rest of Pan-Chelonioidea, implying convergent evolution of the sea turtle flipper and other marine adaptations. We find that Chelonioidea probably originated in the North Atlantic, and that the now global distribution of most sea turtle species suggests that the pelagic life phase of extant species is unique to crown Cheloniidae.
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Free pdf:
Victor Beccari, Marc E H Jones, Andrea Villa, Roberta Martino, Sophie Regnault, Frank Glaw & Oliver W M Rauhut (2026)
The axial skeleton of the tuatara (Rhynchocephalia: Sphenodon): insights on intraspecific variability, ontogeny, sexual dimorphism, and remarks on fossil taxa
Zoological Journal of the Linnean Society 206(4) zlaf135
doi: https://doi.org/10.1093/zoolinnean/zlaf135
https://academic.oup.com/zoolinnean/article/206/4/zlaf135/8570147
As the sole living rhynchocephalian, the tuatara (Sphenodon punctatus) provides important comparative information for fossil rhynchocephalians and lepidosaurs in general regarding expected intraspecific variability, ontogeny, and sexual dimorphism. The axial skeleton of Sphenodon punctatus is described here in detail, using Computed Tomography (CT)-scans and a comprehensive sample (N = 33) of different ontogenetic stages and sexes. The new description adds to already existing literature, and confirms some consistent morphological characters, such as number of vertebrae, position of accessory processes, and ossification patterns. We conducted 3D geometric morphometrics analyses to better understand regionalization of the axial skeleton, ontogenetic changes, and sexual dimorphism in Sphenodon. The morphology of presacral vertebrae is influenced by size and shows negative allometry, with increasing relative height of the neural spine, but decreasing relative vertebral width and length in larger individuals. We compare the morphology and ontogenetic implications of Sphenodon with Mesozoic fossil relatives. Some taxa, especially those from the Jurassic of Europe, show substantial differences in number, proportions, and morphology of vertebrae, including shifts in ossification timing, loss of vertebral intercentra, and changes in rib morphology. We highlight osteological features, such as ossification timing and morphology, that may correlate with taxonomy, systematics, and ecomorphology of Mesozoic rhynchocephalians.
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