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Ankylosaur hyobranchial apparatus resembled that of birds



Ben Creisler
bcreisler@gmail.com


A new online paper:


Robert V. Hill, Michael D. D'Emic, G. S. Bever and Mark A. Norell (2015)
A complex hyobranchial apparatus in a Cretaceous dinosaur and the
antiquity of avian paraglossalia.
Zoological Journal of the Linnean Society (advance online publication)
DOI: 10.1111/zoj.12293
http://onlinelibrary.wiley.com/doi/10.1111/zoj.12293/abstract



The highly specialized feeding apparatus of modern birds is
characterized in part by paraglossalia, triangular bones or cartilages
in the tongue that constitute part of the rarely fossilized
hyobranchial apparatus. Here, we report on a new, juvenile specimen of
the ankylosaurid dinosaur Pinacosaurus grangeri Gilmore, 1933 that
provides the first evidence of paraglossalia outside of crown group
Aves. The specimen is remarkable in preserving a well-ossified
hyobranchial apparatus, including paired paraglossalia, first and
second ceratobranchials, epibranchials, and evidence of a median
cartilaginous basihyal. Reassessment of Edmontonia, another
ankylosaur, also reveals evidence of bony paraglossalia. Ankylosaur
paraglossalia closely resemble those of birds, but are relatively
larger and bear prominent muscle scars, supporting the hypothesis that
ankylosaurs had fleshy, muscular tongues. The other hyobranchial
elements, surprisingly, resemble those of terrestrially feeding
salamanders. Ankylosaurs had reduced, slowly replacing teeth, as
evidenced from dental histology, suggesting that they relied greatly
on their tongues and hyobranchia for feeding. Some curved, rod-like
elements of other dinosaur hyobranchia are reinterpreted as second
ceratobranchials, rather than first ceratobranchials as commonly
construed. Ankylosaurs provide rare fossil evidence of deep homology
in vertebrate branchial arches and expose severe biases against the
preservation and collection of the hyobranchial apparatus. In light of
these biases, we hypothesize that paraglossalia were present in the
common ancestor of Dinosauria, indicating that some structures of the
highly derived avian feeding apparatus were in place by the Triassic
Period.