Re: Yixian Dating Again

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

> One's personal preference to
> relationship of forms does not always mean this is evidence.
> *Sinosauropteryx* may be a compsognathid, *Protarchaeopteryx* may be more
> archie-like than others accept.

Fair enough, but present evidence.  Just saying a taxon could be related to
another taxon won't make my point any less valid.  Especially considering
that I tried not to utilize my preferences when assigning Yixian taxa to
clades in my previous post.  Note Sinornithosaurus and Microraptor were both
only eumaniraptorans, and not avialans which I believe them to be.
Furthermore, I even said that supposed compsognathids are known from the
Early Cretaceous.

Sinosauropteryx is supposedly compsognathid based on (Currie and Chen,
2001)-
1. large skull
Plesiomorphic, being seen in tyrannosaurids and allosauroids as well for
instance.
2. unserrated premaxillary teeth
As in Ornitholestes and plenty of maniraptoriformes
3. slender cervical ribs
A mix of six-relatedness and plesiomorphy, as see in Scipionyx for instance
(both large taxa are especially maniraptoriformes have robust cervical
ribs).
4. fan-shaped dorsal neural spines
Not as unique as originally thought, Sinosauropteryx having mostly posterior
expansions.  Scipionyx also has prominent posterior expansions and
Ornitholestes has a more weakly developed form.
5. short forelimbs (hum+rad/fem+tib <45%)
Plesiomorphic, as seen in Coelurus, Nqwebasaurus, tyrannosauroids,
carnosaurs and more basal taxa.
6. large olecranon process
Plesiomorphic, as seen in carnosaurs and tyrannosaurids, though
Sinosauropteryx's extremely well developed one may be autapomorphic
(Compsognathus' is much weaker).
7. manual phalanx I-1 diameter greater than radius
True, this could be a compsognathid synapomorphy (rather hard to tell in
Nqwebasaurus though).
8. reduced anterior pubic foot
Plesiomorphic, as seen in Monolophosaurus, sinraptorids, Coelurus, Scipionyx
and Nqwebasaurus.
9. prominent obturator process
Poorly defined, many maniraptorans have larger ones, and Sinosauropteryx's
isn't even triangular.

Similarily, present evidence for an archaeopterygid Protarchaeopteryx.  Greg
Paul (2002) has done so, and you and I both agreed the characters were
nearly all plesiomorphies.  I'll go into this in detail if anyone asks, but
don't have the time now.

> <Not really, we have no Jurassic segnosaurs, oviraptorosaurs,
> pygostylians,>
>
>   Not provable. Non preserved, named, described, or recognized. You think
> a segnosaur from the Jurassic would look like a segnosaur from the
> Cretaceous? The very fact that phylostratigraphy supports a LK or MK
> divergence of most maniraptorans indicates we most likely will find these.
> There are "enigmosaur" material from the Morrison, but to know whether
> this is basal segnosaur, stem-"enigmosaur", or basal oviraptorosaur, is
> not something we can tell. *Koparion* does not look like any known
> troodontid tooth, has many unique features. It could even belong to a
> similar, eumaniraptoran group. But that's not really the point. descriebd
> taxa do not define the multitude or even the extent. Phylostratigraphy is
> hardly an exact science, and to use it either way is to add problems to
> the results, bvut ti does help in determining 1) first appearances, 2)
> timing of descent, 3) speciation patterns and probabilities, including
> dispersional.

The Morrison enigmosaur is most parsimoniously from the stem, basal to the
segnosaur-oviraptorosaur split.  I don't know why people have such a problem
with Koparion being a troodontid.  Sure it COULD be a troodontid-mimic, but
pretty much any poorly known taxon faces similar problems and I don't see
people whining about them (Caenagnathasia COULD be an otherwise disimilar
taxon with a convergently oviraptorosaur-like dentary :-)  ).  However,
you're perfectly correct to say that just because all your taxa are known
from the Cretaceous, that they couldn't be present in a more basal form in
the Jurassic.  Which is why I don't trust biostratigraphy with such large
taxonomic groups involved, it's inherently uncertain.  My entire point was
that despite the crappiness of this type of biostratigraphy, even it
supports a Cretaceous age.  Not that it's very good evidence for such an age
(we have radiometric stuff for that, which I don't understand well enough to
argue about), but that Jurassic supporters can't use it as evidence either.

Mickey Mortimer