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[dinosaur] Typothorax (Aetosauria) cranial anatomy and dentition + Conjunctio (Permian temnospondyl) phylogeny




Ben Creisler
bcreisler@gmail.com

New papers:

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William A. Reyes, William G. Parker & Adam D. Marsh (2021)
Cranial Anatomy and Dentition of the Aetosaur Typothorax coccinarum (Archosauria: Pseudosuchia) from the Upper Triassic (RevueltianâMid Norian) Chinle Formation of Arizona.
Journal of Vertebrate Paleontology Article: e1876080
doi: https://doi.org/10.1080/02724634.2020.1876080
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1876080


Our understanding of Typothorax coccinarum is primarily based on postcranial material, along with a few isolated cranial elements. Here we describe the first complete articulated skull of Typothorax coccinarum from the Owl Rock Member of the Late Triassic Chinle Formation in Petrified Forest National Park. We assessed the relationships and defining synapomorphies for some of the major clades within Aetosauria by using a combination of morphological characters in the cranium of Typothorax coccinarum. Based on the descriptions of skulls from a variety of aetosaur species including Aetosaurus ferratus, Aetosauroides scagliai, Coahomasuchus chathamensis, Neoaetosauroides engaeus, Paratypothorax andressorum, Stagonolepis olenkae, Stenomyti huangae, Scutarx deltatylus, and now Typothorax coccinarum, it is apparent that the two major aetosaurian clades vary in their overall skull morphologies. The stagonolepidoids share a more robust, elongate skull, with varying degrees in the lateral expansion of the premaxillary tips. On the other hand, aetosaurines share an overall shorter, more gracile skull with tapered premaxillae. These new characters are mapped onto a revised phylogenetic tree for the Aetosauria. Historically, aetosaurs were interpreted as being predominantly herbivorous. In recent years, the discovery of new aetosaur cranial material, like that of Neoaetosauroides engaeus and Aetosauroides scagliai, suggested an omnivorous diet for at least some aetosaur taxa. The dentition of Typothorax coccinarum possesses the most strongly developed heterodonty for an aetosaur, therefore challenging the historical interpretation by expanding the range of dentition types within Aetosauria. This supports the more recent hypothesis that aetosaurs exhibited diverse feeding strategies beyond just herbivory.

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Bryan M. Gee, David S Berman, Amy C. Henrici, Jason D. Pardo & Adam K. Huttenlocker (2021)
New Information on the Dissorophid Conjunctio (Temnospondyli) Based on a Specimen from the Cutler Formation of Colorado, U.S.A.
Journal of Vertebrate Paleontology ÂArticle: e1877152
doi: https://doi.org/10.1080/02724634.2020.1877152
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1877152


The dissorophid genus Conjunctio (Temnospondyli) is poorly characterized, known only from two incomplete specimens from the upper El Cobre Canyon Formation (lower Permian), Cutler Group, New Mexico, U.S.A. Nonetheless, the taxonâs conserved morphology and stratigraphic occurrence near the CarboniferousâPermian boundary (ca. 299 million years ago) make it an important datum to resolve the early diversification of dissorophids. We report the first occurrence of Conjunctio cf. C. multidens in the adjacent undivided Cutler Formation of San Miguel County, Colorado, which also represents only the second dissorophid from southwestern Coloradoâs historic Placerville assemblage. The new specimen highlights the plesiomorphic anatomy of Conjunctio, with newly described mandibular and postcranial data, and provides further evidence for a relationship to the Eucacopinae. We performed a phylogenetic analysis of 34 temnospondyl taxa by modifying a previously published matrix of 102 craniodental and postcranial characters, scoring Conjunctio at the specimen-level, and found a monophyletic Conjunctio at the base of Eucacopinae. The clade also included the earliest Permian Reiszerpeton and Scapanops in relatively basal positions, and an unresolved polytomy among the later Permian Cacops, Kamacops, Zygosaurus, and Anakamacops. Geographically, the discovery of Conjunctio among the Placerville assemblage is consistent with a broader southwestern U.S. Wolfcampian fauna, correlative to that of the upper El Cobre Canyon Formation in northern New Mexico, and may underscore previously proposed regional provincialism among early Permian tetrapod assemblages.

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