[dinosaur] Diadectomorphs and seymouriamorphs as amniotes from inner ear morphology

Ben Creisler
[email protected]

A new paper:

Jozef Klembara,  Miroslav Hain,  Marcello Ruta,  David S Berman,  Stephanie
E. Pierce  & Amy C. Henrici (2019)
Inner ear morphology of diadectomorphs and seymouriamorphs (Tetrapoda)
uncovered by high‐resolution x‐ray microcomputed tomography, and the origin
of the amniote crown group.
Palaeontology (advance online publication)
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1111_pala.12448&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=f5JfTKWyJ9qEgQvwT0eeT7YWaJkKDFIc030qZn2DFhY&s=w03kcZdAqWJ_Mc2d771aTig7NyYLu1RegFohKwzG3Vw&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__onlinelibrary.wiley.com_doi_full_10.1111_pala.12448&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=f5JfTKWyJ9qEgQvwT0eeT7YWaJkKDFIc030qZn2DFhY&s=KIga3UYLXfG7KEmnqC9Gw6rz6IBHMBVALp5zrtPoTYY&e= 
Data in support of this study are available at the Dryad Digital
Repository: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.5061_dryad.4j2tp4s&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=f5JfTKWyJ9qEgQvwT0eeT7YWaJkKDFIc030qZn2DFhY&s=S00W87M2uhIVRWwdAHuKwfMyLfS9pWjfLTB1YpT3yLs&e= 


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.

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