Dimetrodon teutonis osteohistology + Prozostrodon (Triassic cynodont) postcranial anatomy and osteohistology (free pdfs)
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Ben Creisler
Jun 16, 2026, 1:37:07 PM (3 days ago) Jun 16
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Ben Creisler
Iasmim M. Michelotti, Lívia Roese-Miron, Brodsky Dantas Macedo Farias, Marina Bento Soares, Leonardo Kerber (2026)
Postcranial anatomy and osteohistology of an early prozostrodont cynodont from the Upper Triassic of Brazil
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.70245
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70245
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.70245
Prozostrodon brasiliensis, a probainognathian cynodont of the clade Prozostrodontia, is recognized as a key taxon for understanding the origin of Mammaliaformes and mammals. Despite detailed investigations of its cranial anatomy, the postcranial skeleton has received comparatively less attention. In this contribution, we present a multi-proxy approach to study new postcranial elements assigned to an individual of P. brasiliensis from the Marchezan outcrop (Hyperodapedon Assemblage Zone of Santa Maria Supersequence, Upper Triassic, Rio Grande do Sul, Brazil), integrating anatomical, osteohistological, and phylogenetic data. The analyzed elements include parts of the pectoral girdle (left scapulocoracoid and left clavicle), forelimb (right and left humeri), hindlimb (left femur, tarsal, and metatarsal elements), and caudal vertebrae. The postcranial skeleton exhibits a mosaic of plesiomorphic and derived features, indicating an intermediate morphological (and possibly functional) condition within Prozostrodontia. The anatomy of the scapulocoracoid and humerus suggests a transitional forelimb posture, whereas the femur and hindfoot indicate a generalized, predominantly terrestrial locomotor pattern. Elongated amphicoelous caudal vertebrae further suggest a proportionally long and functional tail, likely contributing to balance and body stabilization. Osteohistological analyses of the humerus and femur show predominance of a woven-parallel complex, consistent with relatively high growth rates. The presence of two growth lines indicates cyclical deposition, whereas the absence of an external fundamental system (EFS) and the lack of a marked decrease in vascularization suggest that the individual had not yet reached skeletal maturity at the time of death. A phylogenetic analysis was performed incorporating newly defined humeral characters and a revised set of postcranial characters modified from previous datasets. Phylogenetic mapping of postcranial characters reveals recurrent patterns of homoplasy within Probainognathia, highlighting the anatomical diversity of non-mammaliaform cynodonts. Together, these results provide new insights into the postcranial record of Prozostrodon brasiliensis and reinforce its significance for understanding the postcranial evolution of the mammal forerunners.
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New synapsid papers:
Free pdf:
Aurore Canoville, Philipp L. Knaus, Lorenzo Marchetti & Jörg Fröbisch (2026)
Contrasting life history in the diminutive Dimetrodon species from North America and Germany
Scientific Reports 16: 16279
doi: https://doi.org/10.1038/s41598-026-52199-y
https://link.springer.com/article/10.1038/s41598-026-52199-y
The sphenacodontid Dimetrodon is best known from lower Permian marginal-marine deposits of North America (NA), where it occupied apex predator roles in aquatic-based food chains. Dimetrodon teutonis, the smallest documented species and only known representative of this genus outside NA, comes from the fully terrestrial and resource-limited ecosystem of the upper Asselian Bromacker locality, Germany. To evaluate its growth strategy and diminutive nature, we present the first osteohistological analysis of D. teutonis. We also reassess NA material from four localities spanning distinct depositional settings. In contrast to the thick and highly vascularized woven to parallel-fibered bone cortices of most NA species, including the small-bodied D. natalis, D. teutonis exhibits thin cortices composed of poorly vascularized parallel-fibered bone. The presence of an external fundamental system indicates somatic maturity and confirms its diminutive nature. These data suggest extended and slow growth throughout ontogeny, likely linked to seasonal resource limitation and low predation pressure in the unique Bromacker ecosystem. In contrast, NA diminutive species inhabiting lowland ecosystems grew rapidly and matured early, in response to competition and high predation pressure. These contrasting life histories in small Dimetrodon species reflect differing ecological pressures and illustrate diverging evolutionary pathways to dwarfism in this iconic genus.
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Aurore Canoville, Philipp L. Knaus, Lorenzo Marchetti & Jörg Fröbisch (2026)
Contrasting life history in the diminutive Dimetrodon species from North America and Germany
Scientific Reports 16: 16279
doi: https://doi.org/10.1038/s41598-026-52199-y
https://link.springer.com/article/10.1038/s41598-026-52199-y
The sphenacodontid Dimetrodon is best known from lower Permian marginal-marine deposits of North America (NA), where it occupied apex predator roles in aquatic-based food chains. Dimetrodon teutonis, the smallest documented species and only known representative of this genus outside NA, comes from the fully terrestrial and resource-limited ecosystem of the upper Asselian Bromacker locality, Germany. To evaluate its growth strategy and diminutive nature, we present the first osteohistological analysis of D. teutonis. We also reassess NA material from four localities spanning distinct depositional settings. In contrast to the thick and highly vascularized woven to parallel-fibered bone cortices of most NA species, including the small-bodied D. natalis, D. teutonis exhibits thin cortices composed of poorly vascularized parallel-fibered bone. The presence of an external fundamental system indicates somatic maturity and confirms its diminutive nature. These data suggest extended and slow growth throughout ontogeny, likely linked to seasonal resource limitation and low predation pressure in the unique Bromacker ecosystem. In contrast, NA diminutive species inhabiting lowland ecosystems grew rapidly and matured early, in response to competition and high predation pressure. These contrasting life histories in small Dimetrodon species reflect differing ecological pressures and illustrate diverging evolutionary pathways to dwarfism in this iconic genus.
=====
Free pdf:
Iasmim M. Michelotti, Lívia Roese-Miron, Brodsky Dantas Macedo Farias, Marina Bento Soares, Leonardo Kerber (2026)
Postcranial anatomy and osteohistology of an early prozostrodont cynodont from the Upper Triassic of Brazil
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.70245
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70245
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.70245
Prozostrodon brasiliensis, a probainognathian cynodont of the clade Prozostrodontia, is recognized as a key taxon for understanding the origin of Mammaliaformes and mammals. Despite detailed investigations of its cranial anatomy, the postcranial skeleton has received comparatively less attention. In this contribution, we present a multi-proxy approach to study new postcranial elements assigned to an individual of P. brasiliensis from the Marchezan outcrop (Hyperodapedon Assemblage Zone of Santa Maria Supersequence, Upper Triassic, Rio Grande do Sul, Brazil), integrating anatomical, osteohistological, and phylogenetic data. The analyzed elements include parts of the pectoral girdle (left scapulocoracoid and left clavicle), forelimb (right and left humeri), hindlimb (left femur, tarsal, and metatarsal elements), and caudal vertebrae. The postcranial skeleton exhibits a mosaic of plesiomorphic and derived features, indicating an intermediate morphological (and possibly functional) condition within Prozostrodontia. The anatomy of the scapulocoracoid and humerus suggests a transitional forelimb posture, whereas the femur and hindfoot indicate a generalized, predominantly terrestrial locomotor pattern. Elongated amphicoelous caudal vertebrae further suggest a proportionally long and functional tail, likely contributing to balance and body stabilization. Osteohistological analyses of the humerus and femur show predominance of a woven-parallel complex, consistent with relatively high growth rates. The presence of two growth lines indicates cyclical deposition, whereas the absence of an external fundamental system (EFS) and the lack of a marked decrease in vascularization suggest that the individual had not yet reached skeletal maturity at the time of death. A phylogenetic analysis was performed incorporating newly defined humeral characters and a revised set of postcranial characters modified from previous datasets. Phylogenetic mapping of postcranial characters reveals recurrent patterns of homoplasy within Probainognathia, highlighting the anatomical diversity of non-mammaliaform cynodonts. Together, these results provide new insights into the postcranial record of Prozostrodon brasiliensis and reinforce its significance for understanding the postcranial evolution of the mammal forerunners.
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