Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT

Abstract

Lysorophians are a group of early tetrapods with extremely elongate trunks, reduced limbs, and highly reduced skulls. Since the first discovery of this group, general similarities in outward appearance between lysorophians and some modern lissamphibian orders (specifically Urodela and Gymnophiona) have been recognized, and sometimes been the basis for hypotheses of lissamphibian origins. We studied the morphology of the skull, with particular emphasis on the neurocranium, of a partial growth series of the lysorophian Brachydectes newberryi using x-ray micro-computed tomography (μCT). Our study reveals similarities between the braincase of Brachydectes and brachystelechid recumbirostrans, corroborating prior work suggesting a close relationship between these taxa. We also describe the morphology of the epipterygoid, stapes, and quadrate in this taxon for the first time. Contra the proposals of some workers, we find no evidence of expected lissamphibian synapomorphies in the skull morphology in Brachydectes newberryi, and instead recognize a number of derived amniote characteristics within the braincase and suspensorium. Morphology previously considered indicative of taxonomic diversity within Lysorophia may reflect ontogenetic rather than taxonomic variation. The highly divergent morphology of lysorophians represents a refinement of morphological and functional trends within recumbirostrans, and is analogous to morphology observed in many modern fossorial reptiles.

A redescription of Orovenator mayorum (Sauropsida, Diapsida) using high‐resolution μCT, and the consequences for early amniote phylogeny

“…; Maddin et al . ), an observation supported by burrows containing the putative recumbirostran Brachydectes newberryi (Pardo & Anderson ). Otherwise, there are several examples of burrowing associated with therapsids from the middle to late Permian (Guadalupian/Lopingian), such as helical burrows containing specimens of Diictodon (Smith ), fossorial adaptations in cistecephalid dicynodonts (Nasterlack et al .…”

Cranial ornamentation of a large Brachydectes newberryi (Recumbirostra: Lysorophia) from Linton, Ohio.

“…Molgophids (Wellstead 1991(Wellstead , 1998Pardo and Anderson 2016;Pardo et al 2017) are highly elongated, limb-reduced, serpentine Permo-Carboniferous 'lepospondyl' tetrapods. The current understanding of the phylogenetic relationship of Molgophidae is as a highly derived recumbirostran group that constitutes the sister clade to the Brachystelechidae (Gleinke 2013(Gleinke , 2015Pardo et al 2015Pardo et al , 2017.…”

“…The current understanding of the phylogenetic relationship of Molgophidae is as a highly derived recumbirostran group that constitutes the sister clade to the Brachystelechidae (Gleinke 2013(Gleinke , 2015Pardo et al 2015Pardo et al , 2017. Recently, micro-computed x-ray tomography (μCT) of the cranial anatomy of the molgophid Brachydectes newberryi Cope (1868) revealed the presence of derived amniote characters of the braincase and suspensorium (Pardo and Anderson 2016). Pardo and Anderson (2016) also argued that the highly reduced cranial morphology of molgophids is analogous to cranial morphology seen in extant fossorial reptiles, including microteiids, lacertoids, and some skinks.…”

“…Recently, micro-computed x-ray tomography (μCT) of the cranial anatomy of the molgophid Brachydectes newberryi Cope (1868) revealed the presence of derived amniote characters of the braincase and suspensorium (Pardo and Anderson 2016). Pardo and Anderson (2016) also argued that the highly reduced cranial morphology of molgophids is analogous to cranial morphology seen in extant fossorial reptiles, including microteiids, lacertoids, and some skinks. In this respect, molgophid morphology is consistent with functional adaptations to fossorial lifestyle common to Recumbirostra as a whole (Bolt and Wassersug 1975;Maddin et al 2011;Huttenlocker et al 2013;Szostakiwskyj et al 2015).…”

“…In this respect, molgophid morphology is consistent with functional adaptations to fossorial lifestyle common to Recumbirostra as a whole (Bolt and Wassersug 1975;Maddin et al 2011;Huttenlocker et al 2013;Szostakiwskyj et al 2015). Moreover, Pardo and Anderson (2016) noted that features previously considered autapomorphic in the molgophid taxa Brachydectes newberryi, Brachydectes elongatus, and Pleuroptyx clavatus (Wellstead 1991(Wellstead , 1998 more likely represented ontogenetic morphological variants (ontogimorphs) rather than true taxonomic variation. This last point led the authors to provisionally assign all known material of Brachydectes newberryi, B. elongatus, and Pleuroptyx clavatus to a single taxon, Brachydectes newberryi, although as the authors themselves note, this is somewhat problematic given considerable vertebral variation among specimens collected from Upper Carboniferous cannel coal localities (Wellstead 1991(Wellstead , 1998Pardo and Anderson 2016).…”