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

PLoS One. 2016 Aug 26;11(8):e0161823. doi: 10.1371/journal.pone.0161823. eCollection 2016.

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.

MeSH terms

  • Amphibians / anatomy & histology
  • Amphibians / classification
  • Animals
  • Fossils*
  • Models, Anatomic
  • Phylogeny
  • Reptiles / anatomy & histology*
  • Reptiles / classification*
  • Skull / anatomy & histology*
  • X-Ray Microtomography

Grants and funding

This research was supported by National Science and Engineering Council of Canada Discovery Grant 327756-2011 awarded to JSA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.