Supradapedon revisited: geological explorations in the Triassic of southern Tanzania

The upper Triassic deposits of the Selous Basin in south Tanzania have not been prospected for fossil tetrapods since the middle of last century, when Gordon M. Stockley collected two rhynchosaur bone fragments from the so called “Tunduru beds”. Here we present the results of a field trip conducted in July 2015 to the vicinities of Tunduru and Msamara, Ruvuma Region, Tanzania, in search for similar remains. Even if unsuccessful in terms of fossil discoveries, the geological mapping conducted during the trip improved our knowledge of the deposition systems of the southern margin of the Selous Basin during the Triassic, allowing tentative correlations to its central part and to neighbouring basins. Moreover, we reviewed the fossil material previously collected by Gordon M. Stockley, confirming that the remains correspond to a valid species, Supradapedon stockleyi, which was incorporated into a comprehensive phylogeny of rhynchosaurs and found to represent an Hyperodapedontinae with a set of mostly plesiomorphic traits for the group. Data gathered form the revision and phylogenetic placement of Su. stockleyi helps understanding the acquisition of the typical dental traits of Late Triassic rhynchosaurs, corroborating the potential of hyperodapedontines as index fossils of the Carnian-earliest Norian.


-CHARACTER LIST
Character list used in the parsimony analysis. Characters modified from previously published analyses, and new characters are acknowledged accordingly. Characters 70 and 76 are treated as additive.
14. Rostral extension of the anguli oris crest: restricted to the main body of the jugal (0); extending onto the rostral process of the jugal, but not the maxilla (1); extending onto the maxilla, but not the rostral process of the jugal (2) (modified from Benton, 1984).
29. Caudal extension of the caudal process of the postorbital: considerably rostral to the level of the caudal border of the infratemporal fenestra (0); at level with the caudal border of the infratemporal fenestra (1) (modified from Dilkes, 1998).

Parietal body: not expanded laterally at midlength
40. Squamosal medial process: short, forming less than half of the caudal border of the supratemporal fenestra (0); long, forming entire or almost entire caudal border of the supratemporal fenestra (1) (Butler et al. 2015).
45. Pterygoid midline suture length: greater than or equal to the distance between the caudal margin of the suture and the basipterygoid articulation (0); less than the distance between the caudal margin of the suture and the basipterygoid articulation (1) (Whatley, 2005).
Obs.: this character surely has some degree of overlap with the previous one, as taxa with fewer tooth rows medial to the main maxillary groove at the caudal half of the maxilla (states "0" and "1" of char. 70) will tend also to have fewer tooth rows on the rostral half of the maxilla (state "1" of char. 71). Yet, taxa with a single (state "0" of char. 70) or even two (state "1" of char. 70) tooth rows medial to the main maxillary groove may also have four or more tooth rows on the rostral half of the maxilla (state "0" of char. 71), because of a higher number of tooth rows lateral to the main maxillary groove. On the contrary, 72. Maxillary lingual teeth: absent (0); present (1) (Benton, 1984).
122. Size of teeth in rows L1 and L2: same size as other teeth (0), teeth in L1 or L2 larger than other teeth (1) (new character).