A Galloanserine Quadrate from the Late Cretaceous Lance Formation of Wyoming

Abstract

Although the monophyly and Cretaceous origins of galloanserines have been established beyond a reasonable doubt, no stem galloanserine has ever been identified and very few fossils help to date the early phylogeny of the clade. We describe a very late Cretaceous quadrate that was previously assigned to Cimolopteryx, a charadriiform genus, and identify it instead as galloanserine and probably stem anseriform. In addition to the presence of a distinctive galloanserine character complex, the quadrate shows a predominance of plesiomorphic characters that are widespread among the Neornithes and shared by Presbyornis and primitive galliforms, in particular the megapodiids. Only one character, the unique configuration of the mandibular condyle, is known only in the anseriforms and thus indicates that the quadrate most likely belongs to a stem anseriform. The bone comes from a bird that compares in size to the smallest living galliforms, which suggests that early anseriforms, and possibly all galloanserines, were small. Their size may be responsible for the paucity of their Cretaceous record and, thus, its incongruence with the molecular dating of the anseriform-galliform divergence.