DOI: 10.5061/dryad.4j2tp4s
title: Data from: Inner ear morphology of diadectomorphs and seymouriamorphs (Tetrapoda) uncovered by high‐resolution x‐ray microcomputed tomography, and the origin of the amniote crown group

description: The origin of amniotes was a key event in vertebrate evolution, enabling
 tetrapods to break their ties with water and invade terrestrial
 environments. Two pivotal clades of early tetrapods, the diadectomorphs
 and the seymouriamorphs, have played an unsurpassed role in debates about
 the ancestry of amniotes for over a century, but their skeletal morphology
 has provided conflicting evidence for their affinities. Using
 high-resolution X-ray microcomputed tomography, we reveal the
 three-dimensional architecture of the well preserved endosseous labyrinth
 of the inner ear in representative species belonging to both groups. Data
 from the inner ear are coded in a new cladistic matrix of stem and
 primitive crown amniotes. Both maximum parsimony and Bayesian inference
 analyses retrieve seymouriamorphs as derived non-crown amniotes and
 diadectomorphs as sister group to synapsids. If confirmed, this sister
 group relationship invites re-examination of character polarity near the
 roots of the crown amniote radiation. Major changes in the endosseous
 labyrinth and adjacent braincase regions are mapped across the transition
 from non-amniote to amniote tetrapods, and include: a ventral shift of the
 cochlear recess relative to the vestibule and the semicircular canals;
 cochlear recess (primitively housed exclusively within the opisthotic)
 accommodated within both the prootic and the opisthotic; development of a
 distinct fossa subarcuata. The inner ear of seymouriamorphs foreshadows
 conditions of more derived groups, whereas that of diadectomorphs shows a
 mosaic of plesiomorphic and apomorphic traits, some of which are
 unambiguously amniote-like, including a distinct and pyramid-like cochlear
 recess.
description: Diadectes MNG
 8747Video 1. Posterior
 portion of skull of Diadectes absitus, MNG 8747: Virtual 3D reconstruction
 of posterior half of skull with 3D virtual reconstruction of endosseous
 labyrinth. Vestibule and semicircular canals, blue; cochlear recess, red;
 fenestra vestibuli, yellow.Seymouria MCZ
 1086Video 2. Posterior
 portion of skull of Seymouria baylorensis, MCZ 1086: Virtual 3D
 reconstruction of posterior half of skull with 3D virtual reconstruction
 of endosseous labyrinth. Vestibule and semicircular canals, blue; cochlear
 recess, red; fenestra vestibuli, yellow.Diadectes Palaeontology
 LchList of
 charactersDiadectes Palaeontology
 DMData
 MatrixDiadectes MNG 8747
 slicesRaw data from CT
 scanDiadectes MNG 8747 scan
 parametersspecimen information
 & scan parametersOrobates MNG 10181 scan
 parametersspecimen information
 & scan parametersOrobates MNG 10181 inner
 earmodel in STL
 formatDiadectes MNG 8747 inner
 earModel in STL
 formatOrobates MNG 10181
 DICOMRaw data from CT
 scanSeymuria MCZ 1086 scan
 parametersspecimen information
 & scan parametersSeymuria MCZ 1086 inner
 earmodel in STL
 formatSeymuria MCZ 1086
 DICOMRaw data from CT
 scanLabidosaurus CM73370
 scan parametersspecimen information
 & scan parametersLabidosaurus CM73370
 DICOMRaw data from CT
 scanLabidosaurus CM 73371
 scan parametersspecimen information
 & scan parametersLabidosaurus CM 73370-1
 inner earmodel in STL
 formatLabidosaurus CM 73371
 DICOMRaw data from CT
 scanLabidosaurus
 CM73371Video 3. Partial
 braincase composed of two specimens of Labidosaurus hamatus (CM 73370, CM
 73371): Virtual 3D reconstruction of bones containing the endosseous
 labyrinth and 3D virtual reconstruction of endosseous labyrinth and
 flocculus. Vestibule and semicircular canals, blue; cochlear recess, red;
 fenestra vestibuli, yellow.