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Re: [dinosaur] Ichthyornis skull reveals origin of beak
Quote from the paper (references removed):
"As in Aves, the fused, toothless premaxillae are acutely pointed and have a
terminal hook. They occupy only the anteriormost quarter of the rostrum; short
premaxillae restricted to the tip of the snout also characterize stemward
ornithuromorphs, such as Gansus and Iteravis, and therefore appear to have been
the primitive form of the avian beak (Fig. 3b). Neurovascular foramina indicate
the presence of a highly keratinized region of rhamphotheca called the
premaxillary nail, which would have enveloped and accentuated the terminal
hook. Osteological correlates for the additional rhamphothecal plates of extant
birds are absent; therefore, we infer that the nail alone was the original
keratinized beak. The ventral surface of the premaxillae is vaulted dorsally
with a median ridge for a soft-tissue internarial septum (Figs. 1, 2, 3b,
Extended Data Figs. 6, 8 and Supplementary Videos 1, 5), which represents a
plesiomorphic dinosaurian condition that is dissimilar to that of
Hesperornithiformes and Aves, in which a flat palatal shelf is covered by
rhamphotheca."
And indeed, 5 of 7 data matrices support *Ichthyornis* as the sister-group of
Hesperornithes + Neornithes. (One finds the traditional position closer to
Neornithes, another is inconclusive.)
"evolutionary elaboration of the bird brain may have been in service to the
exigencies of avian flight, the most sophisticated and demanding form of
locomotion in the history of vertebrate life."
Except for bat flight, right?