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Re: Details on Ricardoestesia isosceles

Tim Williams wrote-

> I've often wondered if _Ricardoestesia_ might actually be a bird.

The problem with this is that Ricardoestesia has fundamentally non-avian
teeth.  Ricardoestesia has macroscopic serrations and laterally compressed
teeth.  Archaeopteryx and pygostylians have conical or slightly compressed
teeth that lack serrations (Guimarota Archaeopteryx? teeth have microscopic
serrations, but I have not heard of serrations in the Solnhofen material).
Several theropods resemble avians in having labiolingually wide roots
(segnosaurs, Microraptor, Archaeornithoides) or serrationless carinae
(Pelecanimimus, Caudipteryx, mononykines, Byronosaurus, Archaeornithoides).
Also, Ricardoestesia has unfused interdental plates, only known in
Archaeopteryx among avians.  All pygostylians (and several theropods-
ornithomimosaurs, oviraptorosaurs, troodontids, mononykines,
Archaeornithoides) lack interdental plates.

> Says
> Julia Sankey of one tooth (V-6237) "The tooth is indented at the base as
> bird teeth (Currie, personal commun., 1999)."

This can also be seen in the holotype (Currie, Rigby and Sloan 1990; fig.

Ken Kinman wrote-

> Have such indented teeth (waisted?) been found in other non-avian
> theropods?

Yes.  Compsognathus, Pelecanimimus, segnosaurs, Protarchaeopteryx,
Caudipteryx, mononykines, Archaeornithoides, troodontids and Microraptor
have teeth with constricted roots.  Outside Theropoda, Eoraptor,
sauropodomorphs and ornithischians also have constricted roots.  Protoavis
probably also has this character, although the relationships of this animal
are uncertain at the moment.

> If _Ricardoestesia_ is avian,
> it may explain why only teeth and a dentary are known for the genus: the
> rest of the skeleton was so gracile that it was rarely preserved.

The best avian candidate for Ricardoestesia would be Avisaurus or a related
taxon, known from the slightly later Hell Creek Formation.  However, all
known enantiornithines have the avian dental characters noted above, so I
find this synonymy very unlikely.

Mickey Mortimer