RE: Ornitholestes and Enantiornis

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Tue, 18 Dec 2001, Williams, Tim wrote:

> I would point out, that, on the whole, Cretaceous maniraptoriforms, which
> were probably all feathered, show a lower incidence of cranial ornamenation
> than more basal theropods (coelophysoids, ceratosaurids, spinosaurids,
> "megalosaurids", allosaurids, tyrannosaurids)
(If tyrannosaurids are more basal than compsognathids, that is.)
> for which there is no evidence of feathers.  Or at least, these
> non-maniraptoriforms are outside of the clade phylogenetically
> bracketed by theropods *known* to be feathered.

Wow, that's an interesting idea, although there are plenty of
counterexamples (_Oviraptor_, _Buceros_, and _Casuarius_ are feathered and
crested, _Megalosaurus_, _Torvosaurus_, and _Abelisaurus_ are not crested
and probably not feathered).

A rigorous study on this idea would be most interesting.

> >> Enantiornithes WALKER 1981                {*Sinornis* > Neornithes}
>
> >Why on Earth did he anchor it on _Sinornis_ and not on the eponymous
> >_Enantiornis_?
>
> _Enantiornis leali_ is a rather poorly known taxon.

It's not even a _nomen dubium_, though.

> _Sinornis_ provides a much more stable anchor taxon for
> Enantiornithes.  Anchoring clades in non-nominative taxa is actually
> quite common, particularly when the nominative genus is poorly known,
> and possibly non-diagnostic. Ceratopsidae, Hadrosauridae, and
> Titanosauridae come to mind.

It's a horrible, horrible idea, and the draft PhyloCode is rightly against
it. The relationships of basal ornithothoraceans don't seem all that
well-understood to me, and I think such a definition could easily lead to
_Enantiornis_ not being an enantiornithean. We've already seen
_Ornithosuchus_ become a non-ornithosuchian, and if we use Sereno's
definition of _Ceratosauria_ (anchored on _Coelophysis_, IIRC), we might
be seeing _Ceratosaurus_ become a non-ceratosaur!! I think I've also seen
speculation on this list that _Ceratops_ may fall outside
Clade(_Triceratops_ + _Centrosaurus_), or however _Ceratopsidae_ is
defined.

How is _Titanosauridae_ defined?

Higher taxa named after dubious genera are regrettable, but I don't think
just picking a different specifier is a good idea. Either:

1) Abandon the old name. Use _Chasmosauridae_, _Centrosauridae_,
_Lambeosauridae_, _Saltasauridae_, etc.

or

2) Incorporate the _nomen dubium_ into the definition:
        Ceratopsidae = Clade(Ceratops montanus + Chasmosaurus belli + 
Centrosaurus apertus)
        Hadrosauridae = Clade(Hadrosaurus foulkii + Edmontosaurus regalis + 
Saurolophus osborni + Lambeosaurus lambei)
or something like that

I think #2 is usually preferable.

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