Utatsusaurus specimen skeletal morphology + early synapsids from Lower Permian of Brazil
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Ben Creisler
Feb 26, 2026, 12:41:49 PMFeb 26
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Ben Creisler
Kenneth D. Angielczyk, Jörg Fröbisch, Christian F. Kammerer, Roger M. H. Smith, Claudia A. Marsicano, Jason D. Pardo, Martha Richter & Juan. C. Cisneros (2026)
Early synapsids from the Cisuralian (lower Permian) Pedra de Fogo Formation, Parnaíba Basin, Brazil: the first definitive South American “pelycosaurs”
Journal of Vertebrate Paleontology e2621685
doi: https://doi.org/10.1080/02724634.2026.2621685
https://www.tandfonline.com/doi/full/10.1080/02724634.2026.2621685
The paleotropics of Euramerica provide nearly our entire picture of Permo–Carboniferous terrestrial tetrapod evolution. The geographic sampling bias inherent in this record obscures important events, such as the turnover between “pelycosaur”- and therapsid-dominated assemblages. The Cisuralian Pedra de Fogo Formation (PdF) of Brazil is a unique window into Gondwanan tropical to subtropical vertebrate assemblages of this time, including abundant chondrichthyans, actinopterygians, sarcopterygians, and temnospondyls, but the terrestrial tetrapod assemblage reported to date is limited to acleistorhinid stem reptiles and captorhinids. Here we describe the first two specimens of Synapsida from the PdF. One specimen is a natural mold of the cranial face of a posterior dorsal or anterior caudal vertebra. Its large size, amphicoelous centrum, and narrow neural arch with closely set, dorsolaterally angled anterior zygapophyses confirm that it is a synapsid. The second specimen is a natural mold of the medial surface of a partial maxilla. The large caniniform tooth, presence of a supracaniniform buttress lacking a dorsal process, and ventral convexity of the element permit its identification as a member of Sphenacodontia, but the straight, dagger-like caniniform is unusual within the clade. Phylogenetic analysis of the maxilla corroborates its sphenacodont affinities. Besides expanding the phylogenetic diversity of the PdF tetrapod assemblage, the specimens add a new size class (very large terrestrial amniote) and ecological guild (medium-size terrestrial faunivore) to the PdF terrestrial fauna. Together, these fossils hint at the presence of a complex terrestrial ecosystem between expansive, perennial water bodies of sufficient depth to support large aquatic predators.
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New papers:
Kazuko Yoshizawa & Takanobu Tsuihiji (2026)
Skeletal morphology of an early ichthyopterygian, cf. Utatsusaurus hataii, from Japan with an emphasis on CT scan data of the skull
Journal of Vertebrate Paleontology e2621687
doi: https://doi.org/10.1080/02724634.2026.2621687
https://www.tandfonline.com/doi/full/10.1080/02724634.2026.2621687
The Early Triassic Utatsusaurus hataii is one of the earliest ichthyopterygians and shows numerous plesiomorphic features. An ichthyopterygian specimen, NSM-PV-20028, from the Osawa Formation in Miyagi Prefecture, Japan, has long been referred to U. hataii, but it remained undescribed in detail. In the present study, the specimen was re-examined and its referral to this species is tentatively sustained, thus being treated as cf. U. hataii. The present study conducted the first digital segmentation of the skull bones of a specimen referred to this species, based on X-ray computed tomographic (CT) image data; and provided detailed information on the entire skeleton of the specimen, including exceptionally well-preserved pelvic girdle and interclavicle. In addition, the two-dimensional retrodeformation method was applied to the specimen to recover the original skeletal proportion. In the result of phylogenetic analysis, NSM-PV-20028 was recovered in a polytomy with U. hataii, which does not contradict our referral of the specimen. The postcranial skeleton of the studied specimen includes both plesiomorphic characters and derived characters, suggesting a transitional stage to a fully aquatic life, emphasizing the importance of this specimen when discussing aquatic adaptation of ichthyopterygians.
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Skeletal morphology of an early ichthyopterygian, cf. Utatsusaurus hataii, from Japan with an emphasis on CT scan data of the skull
Journal of Vertebrate Paleontology e2621687
doi: https://doi.org/10.1080/02724634.2026.2621687
https://www.tandfonline.com/doi/full/10.1080/02724634.2026.2621687
The Early Triassic Utatsusaurus hataii is one of the earliest ichthyopterygians and shows numerous plesiomorphic features. An ichthyopterygian specimen, NSM-PV-20028, from the Osawa Formation in Miyagi Prefecture, Japan, has long been referred to U. hataii, but it remained undescribed in detail. In the present study, the specimen was re-examined and its referral to this species is tentatively sustained, thus being treated as cf. U. hataii. The present study conducted the first digital segmentation of the skull bones of a specimen referred to this species, based on X-ray computed tomographic (CT) image data; and provided detailed information on the entire skeleton of the specimen, including exceptionally well-preserved pelvic girdle and interclavicle. In addition, the two-dimensional retrodeformation method was applied to the specimen to recover the original skeletal proportion. In the result of phylogenetic analysis, NSM-PV-20028 was recovered in a polytomy with U. hataii, which does not contradict our referral of the specimen. The postcranial skeleton of the studied specimen includes both plesiomorphic characters and derived characters, suggesting a transitional stage to a fully aquatic life, emphasizing the importance of this specimen when discussing aquatic adaptation of ichthyopterygians.
=====
Kenneth D. Angielczyk, Jörg Fröbisch, Christian F. Kammerer, Roger M. H. Smith, Claudia A. Marsicano, Jason D. Pardo, Martha Richter & Juan. C. Cisneros (2026)
Early synapsids from the Cisuralian (lower Permian) Pedra de Fogo Formation, Parnaíba Basin, Brazil: the first definitive South American “pelycosaurs”
Journal of Vertebrate Paleontology e2621685
doi: https://doi.org/10.1080/02724634.2026.2621685
https://www.tandfonline.com/doi/full/10.1080/02724634.2026.2621685
The paleotropics of Euramerica provide nearly our entire picture of Permo–Carboniferous terrestrial tetrapod evolution. The geographic sampling bias inherent in this record obscures important events, such as the turnover between “pelycosaur”- and therapsid-dominated assemblages. The Cisuralian Pedra de Fogo Formation (PdF) of Brazil is a unique window into Gondwanan tropical to subtropical vertebrate assemblages of this time, including abundant chondrichthyans, actinopterygians, sarcopterygians, and temnospondyls, but the terrestrial tetrapod assemblage reported to date is limited to acleistorhinid stem reptiles and captorhinids. Here we describe the first two specimens of Synapsida from the PdF. One specimen is a natural mold of the cranial face of a posterior dorsal or anterior caudal vertebra. Its large size, amphicoelous centrum, and narrow neural arch with closely set, dorsolaterally angled anterior zygapophyses confirm that it is a synapsid. The second specimen is a natural mold of the medial surface of a partial maxilla. The large caniniform tooth, presence of a supracaniniform buttress lacking a dorsal process, and ventral convexity of the element permit its identification as a member of Sphenacodontia, but the straight, dagger-like caniniform is unusual within the clade. Phylogenetic analysis of the maxilla corroborates its sphenacodont affinities. Besides expanding the phylogenetic diversity of the PdF tetrapod assemblage, the specimens add a new size class (very large terrestrial amniote) and ecological guild (medium-size terrestrial faunivore) to the PdF terrestrial fauna. Together, these fossils hint at the presence of a complex terrestrial ecosystem between expansive, perennial water bodies of sufficient depth to support large aquatic predators.
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