Thadeosaurus
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Thadeosaurus is an extinct genus of diapsid reptiles from the late Permian Lower Sakamena Formation (Sakamena Group) of Madagascar. The genus contains a single species, Thadeosaurus colcanapi, known from several specimens preserved as natural molds.
Discovery and naming
The generic name, Thadeosaurus, is an anagram of "Datheosaurus", a synapsid genus to which fossils of the former were initially referred. The specific name, colcanapi, honors J.-M. Colcanap, a French infantry captain and the discoverer of the holotype specimen.[1][2]
Description
Thadeosaurus was a superficially lizard-like reptile, with a remarkably long tail that comprised about two-thirds of the animal's total length of Script error: No such module "convert".. It had long toes, especially on the hind legs, and a strong breast bone.[1][3][2]
Classification
The relationships of Thadeosaurus have been debated since its 1981 description. Prior to receiving a name, the fossil material was provisionally referred to Broomia (now recognized as a millerettid[4]), Tangasaurus, and Datheosaurus (now recognized as a caseid synapsid). In his 1981 publication naming Thadeosaurus and Claudiosaurus, Carroll noted similarities between Thadeosaurus and Youngina, but opted to describe it as a 'primitive' sauropterygian—an 'ancestral taxon' to nothosaurs and plesiosaurs.[1]
In the description of the early Permian reptile Orovenator, the phylogenetic results of Reisz et al. (2011) suggested a close relationship between Thadeosaurus and Youngina, united in the family Younginidae. These results are displayed in the cladogram below:[5]
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In 2025, Valentin Buffa and colleagues thoroughly redescribed the fossil material assigned to Thadeosaurus, and reassessed its phylogenetic position. They identified it as a member of the neodiapsid family Tangasauridae, as the sister taxon to the clade formed by Hovasaurus and Tangasaurus, a position also supported by Philip J. Currie in a publication redescribing Tangasaurus.[6] The results of the strict consensus phylogenetic results of Buffa et al. (2025) are displayed in the cladogram below:[2]
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References
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