Phylogenetic data for: Upside down: ‘Cryobatrachus’ and the lydekkerinid record from Antarctica

Temnospondyl amphibians are a common component of non-marine Triassic assemblages, including in the Fremouw Formation (Lower to Middle Triassic) of Antarctica. Temnospondyls were among the first tetrapods to be collected from Antarctica, but their record from the lower Fremouw Formation has long been tenuous. One taxon, ‘Austrobrachyops jenseni,’ is represented by a type specimen comprising only a partial pterygoid, which is now thought to belong to a dicynodont. A second taxon, ‘Cryobatrachus kitchingi,’ is represented by a type specimen comprising a nearly complete skull, but the specimen is only exposed ventrally, and uncertainty over its ontogenetic maturity and some aspects of its anatomy has led it to be designated as a nomen dubium by previous workers. Here we redescribe the holotype of ‘C. kitchingi,’ an undertaking that is augmented by tomographic analysis. Most of the original interpretations and reconstructions cannot be substantiated, and some are clearly erroneous. Although originally classified as a lydekkerinid, the purported lydekkerinid characteristics are shown to be unfounded or no longer diagnostic for the family. We instead identify numerous features shared with highly immature capitosaurs, a large-bodied clade documented in the upper Fremouw Formation of Antarctica and elsewhere in the Lower Triassic. Additionally, we describe a newly collected partial skull from the lower Fremouw Formation that represents a relatively mature, small-bodied individual and that we provisionally refer to Lydekkerinidae; this specimen represents the most confident identification of a lydekkerinid from Antarctica to date.

Methods
We analyzed both specimens separately in the most recent version of Schoch's (2013) temnospondyl-wide matrix (Schoch et al., 2020). This matrix was selected because of its wide taxonomic coverage, which mitigates any preconceived notions of taxonomic affinities (e.g., to Stereospondyli). We omitted the lissamphibians and lepospondyls included in the original matrix since the question of lissamphibian origins is irrelevant to the position of the Antarctic temnospondyls discussed here. Two OTUs were scored for AMNH FARB 9503: one based on the interpretations of Colbert and Cosgriff (1974) and one based on our revised interpretations. We also added several small-bodied Triassic stereospondyls that share some features with these specimens: the rhinesuchid Broomistega putterilli Shishkin and Rubidge, 2000 (Broom, 1930; Shishkin and Rubidge, 2000); the rhytidosteid Nanolania anatopretia (Yates, 2000); the putative rhytidosteid Laidleria gracilis Kitching, 1958 (Warren,1998b; Dias-da-Silva and Marsicano, 2011); the putative trematosaur Almasaurus habbazi Dutuit, 1976; the lydekkerinid Chomatobatrachus halei Cosgriff, 1974 (Warren et al., 2006); and the lapillopsids Lapillopsis nana and Rotaurisaurus contundo Yates, 1999. Broomistega putterilli, C. halei, Lai. gracilis, and Lap. nana were originally scored by Schoch (2013), but either were excluded from the final analysis of that study, or were not sampled at all in the analysis of Schoch et al. (2020). Schoch's (2013) scores for these four taxa were retained by Pardo et al. (2017); their scores are expanded here for the additional 15 characters added to this matrix by Schoch et al. (2020). Our analysis was performed in PAUP* 4.0b169 (Swofford, 2002), with Greererpeton burkemorani Romer, 1969, and Proterogyrinus scheelei Romer, 1970, as the operational outgroups, a heuristic search using 10,000 random-addition sequence replicates (holding one tree per step), and tree bisection-and-reconnection (TBR). Bootstrapping was performed using 10,000 fast stepwise addition replicates. All characters were equally weighted and unordered following previous iterations of this matrix (Schoch, 2013; Pardo et al., 2017; Schoch et al., 2020).