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| Thadeosaurus colcanapi Carroll 1981 (Madagascar, upper Permian), life reconstruction in riparian environment rich in Glossopteris in Buffa, Jalil, Falconnet et Vincent, 2025. Reconstruction by S. Fernandez (MNHN) |
Abstract
The enigmatic neodiapsid Thadeosaurus colcanapi (Lower Sakamena Formation, southwestern Madagascar), sole species of the genus Thadeosaurus, is revised here. The attribution of 12 of the 21 referred specimens is confirmed, spanning all ontogenetic stages, and the anatomy of Thadeosaurus is redescribed in detail with comments on ontogenetical differences. This new anatomical information is included in an expanded phylogenetical dataset tailored to examine the relationships of Permo-Triassic diapsids. A stem-saurian neodiapsid position is confirmed here for all ‘younginiforms’, which are here recovered paraphyletic, with Youngina representing an earlier-diverging taxon. However, this topology is extremely labile, and the monophyly or paraphyly of ‘younginiforms’ could not be unequivocally supported. In contrast, our analyses provide good support for a monophyletic Tangasauridae including all other ‘younginiforms’. Thadeosaurus is here recovered as a member of the Tangasauridae and as the sister-group to the putative semi-aquatic Tangasaurinae with a moderate degree of support, despite the large amounts of missing data in lesser-known tangasaurids partially obscuring our understanding of tangasaurid interrelationships. Last, Thadeosaurus is considered to have inhabited a nearshore, probably riparian, environment, although it remains unclear whether it was semi-aquatic or fully terrestrial. Further examinations of lesser-known tangasaurids, as well as a novel morphotype identified here in the Lower Sakamena Formation of Madagascar, could provide new evidence to deepen our understanding of the evolution and palaeoecology of the Tangasauridae.
Keywords: Tangasauridae, Thadeosaurus, phylogeny, Neodiapsida, late Permian, Madagascar
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| Thadeosaurus colcanapi Carroll 1981 (Madagascar, upper Permian), holotype MNHN.F.MAP360a, b. A, MNHN.F.MAP360a, dorsal surface of individual preserved as a natural mould. B, silicone cast of A. C, MNHN.F.MAP360b, ventral surface of individual preserved as a natural mould. D, silicone cast of C. Scale bars represent 5 cm. |
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| Thadeosaurus colcanapi Carroll 1981 (Madagascar, upper Permian), late subadult (MNHN.F.MAP349a) and adult (MNHN.F.MAP318a, MNHN.F.MAP341) specimens. A, MNHN.F.MAP349a, ventral surface of individual preserved as a natural mould. B, silicone cast of A. C, MNHN.F.MAP318a, ventral surface of individual preserved as a natural mould; note the presence of a Glossopteris leaf overlying the left hindlimb of the individual. D, silicone cast of C. E, MNHN.F.MAP341, ventral surface of individual preserved as a natural mould. F, silicone cast of E. Scale bars represent 5 cm. |
SYSTEMATIC PALAEONTOLOGY
REPTILIA Laurenti 1768 sensu Modesto & Anderson 2004
DIAPSIDA Osborn 1903
NEOREPTILIA Ford & Benson 2020
NEODIAPSIDA Benton 1985 sensu Reisz et al. (2011a)
Family TANGASAURIDAE Piveteau 1926
Genus Thadeosaurus Carroll 1981
Thadeosaurus colcanapi Carroll 1981
Diagnosis:
Differs from other tangasaurids in the following combination of characters (states indicated in brackets, and ‘*’ indicating unambiguous apomorphies recovered in Analysis U2): transverse flange of pterygoid edentulous (138:0)*; basipterygoid processes oriented laterally (166:1)*; ribs fused to costal facets in posterior dorsal vertebrae (273:1); ectepicondylar foramen fully enclosed by well-developed supinator process (319:2; shared with Hovasaurus boulei); proximal margin of entepicondyle roughly perpendicular to main axis of bone, resulting in angular entepicondyle (323:1; shared with Tangasaurinae); bulbous rugosity on supra-acetabular crest immediately dorsal to acetabulum (352:2)*; internal trochanter convergent with proximal femoral head (360:0)*; epipophyses above postzygapophyses of dorsal vertebrae (406:1)*; caudal pleurapophyses laterally expanded (409:1; shared with Tangasaurinae); pisiform notched distally (419:1)*.
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Thadeosaurus colcanapi Carroll 1981 (Madagascar, upper Permian), life reconstruction in riparian environment rich in Glossopteris (a leaf of which is present on MNHN.F.MAP318a) Reconstruction by S. Fernandez (MNHN) |
Valentin Buffa, Nour-Eddine Jalil, Jocelyn Falconnet and Peggy Vincent. 2025. The neodiapsid Thadeosaurus colcanapi from the upper Permian of Madagascar. Papers in Palaeontology. 11(2); e70008. DOI: doi.org/10.1002/spp2.70008 [23 March 2025]
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