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

Abstract

Temnospondyl amphibians are common in 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, which we provisionally refer to Lydekkerinidae; this specimen represents the most confident identification of a lydekkerinid from Antarctica to date.

The disadvantage of derivation: conserved systematic flaws in primary data have repeatedly biased the phylogenetic inference of Temnospondyli (Tetrapoda, Amphibia)

“…The derivate of Pardo et al (2017) is re-analyzed because this is the only derivate to make substantial taxon and character additions, with 13 new OTUs and 133 new characters. Other derivates have made comparatively few modifications (Strapasson et al, 2014; Dilkes, 2015; Daza et al, 2020; Schoch et al, 2020b; Gee et al, 2021). The expanded taxon sample of Pardo et al includes lissamphibians, and their analysis produced a novel hypothesis of a diphyletic origin of Lissamphibia from within Temnospondyli.…”

“…The phylogeny of temnospondyls and its various subclades has been frequently examined using computer-assisted methods (e.g., Eltink et al, 2017, 2019; Fernández-Coll et al, 2017; Marsicano et al, 2017, 2021; Marzola et al, 2017; Pacheco et al, 2017; Pardo et al, 2017; Chakravorti and Sengupta, 2018; Gee et al, 2018, 2021; Liu, 2018; Schoch, 2018a, 2018b, 2018c, 2019, 2021a, 2021b; Schoch and Witzmann, 2018; Atkins et al, 2019; Buffa et al, 2019; Schoch and Voigt, 2019; Dilkes, 2020; Gee, 2020b, 2021; Maisch, 2020; Schoch et al, 2020a; Werneburg et al, 2020; Schoch and Milner, 2021; Schoch and Sobral, 2021; Arbez et al, 2022; Schoch & Sues, 2022; Werneburg et al, 2022). The large body of work underscores the import of phylogenetic analyses as the means of inferring evolutionary narratives and informing taxonomic frameworks.…”

“…Arrows depict express derivation; dashed arrows depict inferred derivation. Abbreviations for capitosaur analyses: D, Dilkes (2015, 2020); D-01, Damiani (2001); D et al, Daza et al (2020); ESD, Eltink et al (2017); FGD, Fortuny et al (2011a); G, Gee (2021); GMS, Gee et al (2021); GBHPH, Gee et al (2021); HBA, Holmes et al (2013); L, (Liu, 2016, 2018); LW-05 (Liu and Wang, 2005); M, McHugh (2012); M et al (Maganuco et al, 2009); MFEM, Maddin et al (2013); MMSC, Marzola et al (2017); PSH, Pardo et al (2017); S-00, Schoch (2000); S-03, Steyer (2003); S, Schoch (2008b, 2012, 2013 2018c); SS (Schoch and Sues, 2013); SPS, Strapasson et al (2014); SSD (Sidor et al, 2014); SWV, Schoch et al (2020); WSN Witzmann et al (2016); WWSR, Werneburg et al (2022); YW-00, Yates and Warren (2000).…”

“…Finally, the matrix itself has been expanded in several stepwise studies to address lissamphibian origins, under a presumption of origin(s) within Temnospondyli (Pardo et al, 2017;So et al, 2018So et al, , 2021Daza et al, 2020;Schoch et al, 2020b;Kligman et al, 2021). In both these derivates, which were adopted by other workers, and other derivates that were not adopted by a subsequent study (e.g., Strapasson et al, 2014;Dilkes, 2015;Gee et al, 2021;Werneburg et al, 2022), the taxon and character sampling have been variably modified, but virtually all of the original codes of Schoch (2013), and subsequently those introduced for characters added by Pardo et al (2017) and Schoch et al (2020b), have not been modified. There is therefore not only a connectivity in the source of temnospondyl-wide matrices but also a broad consistency in the primary dataset (individual codes).…”