Thadeosaurus

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title: "Thadeosaurus" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["diapsids", "prehistoric-reptile-genera", "permian-reptiles-of-africa", "fossils-of-madagascar", "permian-madagascar", "fossil-taxa-described-in-1981"] description: "Extinct genus of reptiles" topic_path: "general/diapsids" source: "https://en.wikipedia.org/wiki/Thadeosaurus" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Extinct genus of reptiles ::

| fossil_range = Late Permian, | image = Thadeosaurus colcanapi (holotype and cast).jpg | image_caption = Holotype specimen; natural mold (A, C), and silicone cast (C, D) | display_parents = 3 | taxon = Thadeosaurus | authority = Carroll, 1981 | type_species = Thadeosaurus colcanapi | type_species_authority = 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.

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.

Description

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/67/Thadeosaurus_Scale.svg" caption="Size compared to a human hand"] ::

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 cm. It had long toes, especially on the hind legs, and a strong breast bone.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d6/Thadeosaurus_colcanapi_(holotype,_3D_model_based_on_CT_data).jpg" caption="Surface model of the ''T. colcanapi'' holotype, with details not visible in the natural mold and silicone cast shown in blue"] ::

Classification

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/dc/Thadeosaurus_colcanapi_(life_restoration).jpg" caption="Speculative [[life restoration"] ::

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), 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.

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:

|1={{clade |1=Captorhinidae |label2=Diapsida |2={{clade |1=Araeoscelidia |label2=Neodiapsida |2={{clade |1=Orovenator |2={{clade |1=Lanthanolania |2={{clade |label1=Tangasauridae |1={{clade |1=Tangasaurus |2={{clade |1=Acerosodontosaurus |2=Hovasaurus}} }} |2={{clade |label1=Younginidae |1={{clade |1=Thadeosaurus |2=Youngina}} |2={{clade |1=Claudiosaurus |label2=Sauria |2={{clade |1=Archosauromorpha |2=Lepidosauromorpha }} }} }} }} }} }} }} }} }}

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. The results of the strict consensus phylogenetic results of Buffa et al. (2025) are displayed in the cladogram below:

|{{clade |1=Araeoscelidia |2={{clade |1=Varanopidae |label2=Neoreptilia |2={{clade |1=Parareptilia |label2=Neodiapsida |2={{clade |1=Youngina |2={{clade |label1=Tangasauridae |1={{clade |1=Kenyasaurus |2={{clade |1=Acerosodontosaurus |2={{clade |1=Thadeosaurus |label2=Tangasaurinae |2={{clade |1=Hovasaurus |2=Tangasaurus }} }} }} }} |3={{clade |1={{clade |1=Claudiosaurus |label2=Weigeltisauridae |2={{clade |1=Weigeltisaurus |2=Coelurosauravus |3=Rautiania spp. }} }} |label4=Sauria |4={{clade |1={{clade |1=Paliguana |2=Lepidosauria }} |3={{clade |1=Archosauromorpha

References

References

1. (1981). "Plesiosaur ancestors from the Upper Permian of Madagascar". Philosophical Transactions of the Royal Society.
2. (September 1984). "Ontogenetic changes in the eosuchian reptile ''Thadeosaurus''". [[Journal of Vertebrate Paleontology]].
3. (2025-03-03). "New information on the anatomically derived millerettid ''Milleretta rubidgei'' from the latest Permian based on µCT data". [[Zoological Journal of the Linnean Society]].
4. (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B.
5. Currie, P. J.. (1982). "The osteology and relationships of ''Tangasaurus mennelli'' Haughton". Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum.
6. (2025-03-23). "The neodiapsid ''Thadeosaurus colcanapi'' from the upper Permian of Madagascar". [[Papers in Palaeontology]].

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