Stereospondyli, Zittel, 1888

Steyer, Jean-Sébastien, Peecook, Brandon R., Arbez, Thomas, Nesbitt, Sterling J., Tolan, Steve, Stocker, Michelle R., Smith, Roger M. H., Angielczyk, Kenneth D. & Sidor, Christian A., 2021, New data on the Triassic temnospondyls from the Karoo rift basins of Tanzania and Zambia, Geodiversitas 43 (12), pp. 365-376 : 369

Stereospondyli indet.

( Fig. 4 )

REFERRED MATERIAL. — Zambia. NHCC LB678 ( Fig. 4 and Peecook et al. 2018: fig. 4A-C), a partial right mandible of a small-sized, but adult, individual based on the well-developed ornamentation visible on its labial side (e.g., Steyer 2000) ( Fig. 4A ). The specimen was found by one of us (SJN) in 2014 together with small cylindrical vertebrae similar to NHCC LB690-728.

LOCALITY AND HORIZON. — Locality L290 near the village of Sitwe, upper horizon of the Ntawere Formation, Middle-?Late Triassic (e.g., Battail 1993; Hancox 2000; Peecook et al. 2018) of the Luangwa Basin (sensu Barbolini et al. 2016).

DESCRIPTION (see also Peecook et al. 2018)

This small mandibular portion (29 mm in length) preserves three partial bones; a dentary labially and dorsally ( Fig. 4A, B [d]), and two coronoids lingually and dorsally ( Fig. 4B, C [cor1 and cor2]). The partial dentary is wellornamented, and its ornamentation pattern consists of interconnected pits of various sizes. It bears at least 12 marginal tooth sockets, which are slightly laterally compressed (a stereospondyl synapomorphy; e.g., Yates & Warren 2000). The socket Nr. 8 still preserves a partial tooth with its medullar cavity. The two partial coronoids are covered by dense and well-separated denticle patches (c. 3 teeth per mm 2). These denticles are conical, short (<1 mm), and taper to a sharp point. These denticle patches are separated by a depression in the posterior region of the specimen that is visible lingually. The anterior patch is complete and covers most of the length of the specimen. It is supported by the betterpreserved coronoid ( Fig. 4B, C [cor1]). The other denticle patch and its corresponding coronoid ( Fig. 4B, C [cor2]) are partially preserved and only visible in the posterior extremity of the specimen. Due to the fragmentary nature of the specimen, it is not clear if these elements represent pre-, inter- or post-coronoids.

IDENTIFICATION

We identify this specimen as a stereospondyl based on the laterally compressed tooth sockets as well as the stereospondyl synapomorphy of a dentary that does not contribute substantially to the lingual side of the mandible (the dentary is clearly visible in lingual view in basal temnospondyls; e.g., Schoch & Milner 2000). It is difficult to assign a more precise identification because three stereospondyl clades have very dense denticle patches on at least two of their coronoids: the Rhinesuchidae , the Lydekkerinidae , and the Rhytidosteidae (e.g., Mahavisaurus dentatus Lehman, 1966 , Maganuco et al. 2014: figs 8 - 9). Pending more discoveries, we therefore prefer to assign this fragmentary specimen to Stereospondyli .

Figures

FIG. 4. — Partial mandible of Stereospondyli (NHCC LB678) from the Triassic (?Anisian) of Zambia (Luangwa Basin) in labial (A), dorsal (B) and lingual (C) views. Abbreviations: cor1, coronoid 1; cor2, coronoid 2; d, dentary. Scale bar: 10 mm. Modified from Peecook et al. 2018.