Thadeosaurus Temporal range: Late Permian, | |
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Speculative life restoration | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Diapsida |
Clade: | Neodiapsida |
Family: | † Younginidae |
Genus: | † Thadeosaurus Carroll, 1981 |
Type species | |
†Thadeosaurus colcanapi Carroll, 1981 |
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.
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]
Thadeosaurus was a superficially lizard-like reptile, with a remarkably long tail that comprised about two-thirds of the animal's total length of 60 centimetres (24 in). It had long toes, especially on the hind legs, and a strong breast bone. [1] [3] [2]
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]
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]