Stereospondyli Zittel 1888
Creators: name: Steyer, Jean-Sébastien
name: Peecook, Brandon R.
name: Arbez, Thomas
name: Nesbitt, Sterling J.
name: Tolan, Steve
name: Stocker, Michelle R.
name: Smith, Roger M. H.
name: Angielczyk, Kenneth D.
name: Sidor, Christian A.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Amphibia
Stereospondyli

description: cf. Stereospondyli
(Figs 2; 3)
REFERRED MATERIAL. — Tanzania. NMT RB464 - 468 (Fig. 2), five small thoracic intercentra (anteroposterior length of 3.6-5.7 mm) from Locality Z90, mid- to upper Lifua Member, Manda Beds, Middle-?Late Triassic (e.g., Nelsen et al. 2001; Smith et al. 2018) of the Ruhuhu Basin.
Zambia. NHCC LB 647, 679 - 687 (Fig. 3 and Peecook et al. 2018: fig. 4D-E), 10 small atlantal intercentra (L = 4.2 to 8.5 mm); NHCC LB688 - 689, two corresponding axes; and NHCC LB690-728, 39 small thoracic intercentra; all from Locality L82, 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)
All these vertebral elements are fully ossified.
The thoracic intercentra are well preserved, except NMT RB467, which looks anteriorly slightly compressed (Fig. 2). These intercentra are subcylindrical and closed dorsally into a stereospondylous condition. They are subcircular in anterior and posterior views, and subrectangular in lateral view (with a height/length ratio of around 1). Their external surfaces show small ridges and grooves. Anteriorly and posteriorly, notochordal pits are visible, but they do not pass through the whole vertebral bodies. Dorsally, facets for the attachment of the neural arch are also preserved.
The atlantal intercentra (Fig. 3 and Peecook et al. 2018: fig. 4) are relatively wide (l = 6.3 to 11.1 mm) and flat (h = 5 mm max). Their anterior side is biconcave to articulate with the exoccipital condyles, whereas their posterior side is concave. Their dorsal side presents a longitudinal groove for the neural canal.
Both the Tanzanian and Zambian intercentra were found associated with abundant silesaurid (c. thousands of elements in Tanzania) and rare cynodont remains.
IDENTIFICATION
Based on their strong degree of ossification the Tanzanian and Zambian intercentra belong to adult individuals (e.g., Steyer 2000). Their identification beyond Temnospondyli, possibly Stereospondyli, is difficult given that they were found as isolated elements and not associated with more diagnostic material (e.g., skull elements). Moreover, concerning the atlantes, these elements are rare in the temnospondyl fossil record and therefore difficult to assign. The stereospondylous condition of all these intercentra is also found among disparate clades of temnospondyls, including the tupilakosaurids (e.g., Thabanchuia Warren, 1998), metoposaurids, plagiosaurids, and mastodonsaurids
(e.g., Yates & Warren 2000). The Tanzanian and Zambian intercentra are anteroposteriorly elongate, as is the case in metoposaurid stereospondyls (e.g., Hunt 1993; Gee et al. 2018; Buffa et al. 2019; Fortuny et al. 2019). However, this is only one character state, and the shape and proportions of the intercentra vary along a single vertebral column within temnospondyls. Therefore, we conservatively assign the specimens to “cf. Stereospondyli ”. Interestingly, these intercentra belong to small but adult individual(s) and clearly differ from the large, dorsally open intercentra of other temnospondyls from the same rock units (see below). They may correspond to a new small-bodied taxon but we prefer to leave this issue undecided, pending the discovery of additional material.
description: Published as part of 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, pp. 365-376 in Geodiversitas 43 (12) on pages 367-369, DOI: 10.5281/zenodo.4906293