RE: Ornitholestes and Enantiornis

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Stephan Pickering wrote:

>Dilophosaurus's two species, moreover, may be sexually dimorphic
>representatives, crested females to attract males (in this case, males
>being the crestless forms known as Liliensternus) [snip]
>The point is: theropods were logically matrilineal, and "horns",
>"crests", etc. visual signals for smaller, drab males.

This certainly doesn't apply to the extant members of the Theropoda, in
which the males are typically (though not invariably) gaudy and conspicuous
(at least during the breeding season), and the females have a drab plumage.
I'm not saying all extinct theropods were Mesozoic peacocks; but you're
going against the grain of modern avian behavior in describing their extinct
cousins as "logically matrilineal", in which females had to entice males.

Such visual cues on the part of the males are not limited to the plumage in
moderns birds - beaks, wattles and air sacs are also used by male birds to
advertise his health, virility, or availability (or all of the above).
Perhaps this was the purpose of the crests and horns of Mesozoic theropods??

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) 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.

In other words, the maniraptoriform plumage took over from cranial
ornamentation of more basal theropods as the "signboard" of sexual
selection.  I know this is shameless speculation: brickbats are welcome.

T. Mike Keesey wrote:

>> 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.  _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.



Tim


Tim