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Hyomandibulae of Rhizodontids (Sarcopterygii, Stem-Tetrapoda)
 
SVPCA Conference
 
Platform presentation (20 minutes)
Authors
 
*Martin D Brazeau
 
 
Jonathan E Jeffery
 
Abstract
 
In digited stem-tetrapods, the hyomandibular (which plays a central role in feeding and respiration) underwent a major morphological and functional transformation to become the stapes of the middle ear. The hyomandibulae of basal, fish-like, stem-tetrapods can therefore provide data on the primitive conditions preceding this important change. Unfortunately, only a few well-preserved examples are known, hampering wide-ranging comparisons - even though the best-known example (that of the tristichopterid Eusthenopteron; Jarvik, 1954) has been used as an exemplar of fish-like stem-tetrapod hyomandibula morphology, the conditions at the base of the tetrapod radiation remain obscure. We report here four hyomandibulae, from three separate localities, which are referable to the Rhizodontida, the most basal clade of stem-tetrapods. These specimens share a number of characteristics, and are appreciably different from the small number of hyomandibulae reported for other fish-like stem-tetrapods. While it is unclear if these characteristics represent synapomorphies or symplesiomorphies, they highlight the morphological diversity of hyomandibulae within the early evolution of the tetrapod total-group. Well-preserved muscle scarring on some of these hyomandibulae permit inferences of hyoid arch musculature in stem-tetrapods.
London 2020