A lower Carboniferous (Visean) tetrapod trackway represents the earliest record of an edopoid amphibian from the UK

Abstract

The ichnological fossil record has previously provided key evidence for the diversification of land vertebrates (tetrapods) during the Carboniferous Period, following the invasion of the land. Within the UK, tetrapod ichnofossils from the late Carboniferous of the English Midlands are well documented, but few such fossils are known from earlier in the period. We present a rare ichnological insight into early Carboniferous tetrapod diversification in the United Kingdom based on a Viseanaged specimen collected from an interdistributary trough palaeoenvironment at Hardraw Scar, Wensleydale, North Yorkshire. This specimen represents the stratigraphically oldest known tetrapod trackway from the UK. We refer this specimen to Palaeosauropus sp., providing the earliest known occurrence of an edopoid temnospondyl. Supplementing the sparse record of contemporary body fossils from the early Carboniferous, this provides further insights into the diversification of temnospondyl amphibians across Euramerica.Supplementary material: A 3D model of the plaster cast produced from the trackway specimen is available at https://doi.org/ 10.5519/0022377 and a lower resolution version is available on Sketchfab (https://skfb.ly/6OAxR).

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

“…Finally, character 197 of Schoch (2013) referred to manual digit count and was coded for 41 of the 72 taxa sampled by Schoch (2013). Temnospondyls have long been assumed to share a condition of four manual digits (197–1; e.g., Warren and Snell, 1991; Dilkes, 2015; Konietzko-Meier et al, 2020), and this is a common rationale for associating tetradactyl handprints with temnospondyls (e.g., Stimson et al, 2012, 2016; Marsicano et al, 2014; Bird et al, 2020; Cisneros et al, 2020; Mujal and Schoch, 2020). Predictably, every previously coded temnospondyl other than Metoposaurus was coded for a tetradactyl manus; Metoposaurus was only correctly coded as pentadactyl because of personal communication to Schoch (Konietzko-Meier et al, 2020:1153).…”

“…Finally, there is the possibility that known tetrapods not presently considered to be temnospondyls might in fact be temnospondyls and have not been recognized as such because they have only been tested in relatively narrow analyses. This ambiguity can sometimes result from outdated definitions (e.g., Schoch, 2013;Marjanović and Laurin, 2019) but also owes to the paucity of temnospondyl records from the Viséan (e.g., Milner and Sequeira, 1993;Werneburg et al, 2019;Bird et al, 2020) and the disputed affinities of certain Carboniferous taxa (e.g., the "St. Louis tetrapod" of Clack et al, 2012;Caerorhachis, compare Holmes and Carroll, 1977, Ruta et al, 2001, and Pawley, 2006Doragnathus, compare Smithson, 1980, with Clack andMilner, 2015;certain 'lepospondyl' nectrideans, compare Carroll et al, 1998, with Pardo, 2014, which collectively creates ambiguity regarding the earliest stages of temnospondyl evolution. Character sampling.--Neither the original matrix of Schoch (2013) nor any derivate captures all of the characters used in fine-scale analyses at the family or superfamily level.…”