Cranial anatomy and systematics of Dendrerpeton cf. helogenes (Tetrapoda, Temnospondyli) from the Pennsylvanian of Joggins, revisited through micro‐CT scanning

Abstract

The Joggins Fossil Cliffs constitute an upper Carboniferous (Pennsylvanian) locality in Nova Scotia (Canada). This site, known for the rich record of fossils preserved in the palaeoenvironment in which they lived, sheds light on the late Carboniferous environment. More specifically, Joggins records one of the earliest Pennsylvanian ecosystems and is unique in preserving a rich diversity of terrestrial fauna compared with other Pennsylvanian communities, which mostly preserve aquatic fauna. For vertebrate palaeontology, the significance of Joggins lies in the discovery of the earliest amniotes (Hylonomus lyelli Dawson, Protoclepsydrops haplous Carroll, and Asaphestera platyris (Steen)) and the second earliest temnospondyl, Dendrerpeton (only Balanerpeton woodi Milner & Sequeira occurs earlier). Computed tomography of the most complete tetrapod specimen found at Joggins, the temnospondyl amphibian currently referred to Dendrysekos helogenes Steen, made accessible the internal anatomy and revealed previously obscured anatomical structures, including the stapes, scleral plates, and partial sphenethmoid. These newly accessible features enabled a redescription of this specimen. The resulting anatomical comparisons and phylogenetic analyses suggest that the genus Dendrysekos is a junior synonym of Dendrerpeton; the diagnostic characters previously distinguishing the two genera are considered to be instead a combination of ontogenetic and preservational parameters, and the two genera were not resolved as discrete. Additionally, the phylogenetic analyses show that the interrelationships between the main early temnospondyl groups (Edopoidea, Dvinosauria, Eryopoidea and Dissorophoidea) are neither robust nor well supported, due to the low number of shared derived characters.

Computed tomography and three-dimensional reconstruction of the skull of the stem tetrapodCrassigyrinus scoticusWatson, 1929

“…Despite the naming conventions used below, it is unclear whether these fossae are homologous or analogous with the pre- and intercoronoid fossae of earlier stem tetrapods (Jeffrey, 2003), see Discussion for more details. Intercoronoid fossae also occur in some temnospondyls, such as Dendrerpeton (Arbez et al, 2022), suggesting these may be more widely distributed characters. The second fossa is an anteroposteriorly elongate opening at the anterior end of the lower jaw that accommodated the vomerine fang.…”

“…Medical imaging methods, particularly micro-computed tomography (µCT), are increasingly being applied to fossils (Cunningham et al, 2014), including early tetrapods (Arbez et al, 2022;Boisvert et al, 2008;Herbst & Hutchinson, 2019;Pardo et al, 2017;Pierce et al, 2012;Porro et al, 2015aPorro et al, , 2015bRawson et al, 2021). More recently, new techniques have been developed to digitally repair damage and deformation in fossil skulls (Lautenschlager, 2016), including early tetrapod skulls (Porro et al, 2015a(Porro et al, , 2015bRawson et al, 2021).…”

A new eryopid temnospondyl from the Carboniferous–Permian boundary of Germany

“…Thus, our analysis is based on a total number of 26 taxa, including eight taxa referred to as eryopids. Balanerpeton woodi Milner and Sequeira, 1994, Dendrerpeton helogenes Steen, 1934 (Arbez et al, 2022; Dendrysekos helogenes sensu Schoch and Milner, 2014), and Cochleosaurus bohemicus (Fritsch, 1876) served as operational outgroups. We deleted six characters from the original matrix of Schoch (2021b) because of unclear definitions and/or partial redundancies.…”

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

“…The neurocranium remains a poorly sampled region, in large part because this is a historically difficult area to access and thus to code. It is hoped that additional tomographic work in temnospondyls (e.g., Robinson et al, 2005;Čerňanský et al, 2016;Arbez et al, 2017Arbez et al, , 2022Gee et al, 2019a;Gee, 2020a;Marsicano et al, 2021) will produce further clarity in the way that it has for 'microsaurian' lepospondyls (Maddin et al, 2011;Huttenlocker et al, 2013;Pardo et al, 2015;Szostakiwskyj et al, 2015;Pardo and Anderson, 2016;Gee et al, 2019bGee et al, , 2020MacDougall et al, 2021). There are also avenues for expanding certain characters that only capture generalized trends.…”

“…The phylogeny of temnospondyls and its various subclades has been frequently examined using computer-assisted methods (e.g., Eltink et al, 2017Eltink et al, , 2019Fernández-Coll et al, 2017;Marsicano et al, 2017Marsicano et al, , 2021Marzola et al, 2017;Pacheco et al, 2017;Pardo et al, 2017;Chakravorti and Sengupta, 2018;Gee et al, , 2021Liu, 2018;Schoch, 2018aSchoch, , 2018bSchoch, , 2018cSchoch, , 2021aSchoch, , 2021bSchoch and Witzmann, 2018;Atkins et al, 2019;Buffa et al, 2019;Schoch and Voigt, 2019;Dilkes, 2020;Gee, 2020bGee, , 2021Maisch, 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.…”