Dinosaurian Synapomorphies Found In Archaeopteryx

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Dinosaurian Synapomorphies Found In Archaeopteryx

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As promised, here are the derived characters with which Gauthier (in his 1986 paper) unites Archaeopteryx with modern birds, outside of all other theropods (with Gauthier's original clarifiers in parens) [and with my editorial comments in brackets]:

Premaxillae elongate, narrow, and more pointed anteriorly, with longer nasal processes [similar condition in bullatosaurs, and in the nondinosaurian Megalancosaurus, but unique to Archie and later birds in Maniraptora].

Maxillary process of premaxilla reduced so that maxilla participates broadly in external naris (also in troodontids).

Enlarged brain/basicranium (temporal musculature fails to extend origin onto frontal bones [to a certain degree in bullatosaurs and therizinosauroids, and perhaps in some of the newer, "brainier" dromaeosaurids].

Double-condyled quadrate displaced from distal position on opisthotic to more anteromedial position in contact with prootic (Currie, pers. comm. and Walker, pers. comm., disagree with Whetstone's interpretation of the quadrate: Currie notes the anterior displacement of the quadrate in troodontids [maybe Nino can comment on the condition in Pelecanimimus], and Walker does not consider the quadrate to be double-condyled in Archaeopteryx).

Maxillary and dentary teeth reduced in size and number (or lost), with unserrated crowns and enlarged roots that completel...

Submitted by: digitalessays
Date Submitted: 11-21-99 11:50pm
Category: English
Words: 1860
Pages: 7.44