Buitreraptor: not a dromaeosaur, not a sister to Rahonavis

A long-snouted theropod
Buitreraptor gonzalezorum (Makovicky, Apesteguía & Agnolin, 2005, Fig. 1) was recovered as “a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.”

The authors nested
Buitreraptor between Rahonavis and Austroraptor + Unenlagia distinct from troodontids and traditional dromaeosaurs like Velociraptor

Unfortunately 
the large reptile tree  nests Buitreraptor with the troodontid/pre-birds Aurornis and Anchiornis, two taxa published long after the publication of Buiteraptor. Wikipedia does not make this correction. I was unable to find any prior work linking these taxa.

Figure 1. Buitreraptor skull with bones and missing bones colorized.

Figure 1. Buitreraptor skull with bones and missing bones colorized. That naris is enormous! And fragile! The maxillary fenestra, anterior to the antorbital fenestra, is quite large, lightening the long skull.

By comparison
Aurornis (Fig. 2) also has a large naris and maxillary fenestra, but not nearly as large. Aurornis is Late Jurassic. Buitreraptor is Cenomanian (earliest Late Cretaceous). So that evolutionary chronology makes sense.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

Stem like coracoid
Unlike Aurornis, Buitreraptor had an elongated and waisted coracoid, so it is likely that Buitreraptor developped the habit of flapping by convergence with birds, parabirds and pseudo birds.

Rahonavis 
still nests with basal therizinosaurs.

References
Makovicky, PJ, Apesteguía S, Agnolín FL. 2005. The earliest dromaeosaurid theropod from South America. Nature 437: 1007–1011. Bibcode:2005Natur.437.1007Mdoi:10.1038/nature03996PMID 16222297.

 

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