Re: 11th specimen of Archaeopteryx

[Mike Keesey <keesey@gmail.com>]

On Wed, Nov 2, 2011 at 9:58 AM, Jason Brougham <jaseb@amnh.org> wrote:
>
> On Nov 2, 2011, at 1:49 AM, Scott Hartman wrote:
>>
>> Likewise, if you map out paravian phylogeny and and where traits
>> associated with arboreality show up, you'd see that there's simply
>> nothing at all that shows up with Archie.
>
> This statement is the most puzzling one I've read from you. Taking, as one 
> example, the cladogram presented yesterday by Prieto-Marquez, Bolortsetseg, 
> and Horner (A diminutive deinonychosaur (Dinosauria: Theropoda) from the 
> Early Cretaceous of Öösh (Övörkhangai, Mongolia), we see that the closest 
> relative of Archaeopteryx is Jeholornis, which was reported by Zhou and Zhang 
> twice as having a  fully reversed hallux. The next more derived node is 
> Sapeornis, which Glen and Bennett admitted may be an exception to the rule 
> that basal birds foraged on the ground.

What do you mean by "closest"? A cladogram only portrays ancestry and
descent, so the only measure of "closeness" in a cladogram is shared
ancestry. And in that case you have it wrong: the closest relative of
Archaeopteryx is *all* of Clade(Jeholornis + Aves), and the closest
relative of Jeholornis is *all* of Clade(Sapeornis + Aves).

You may have been referring to a different type of "closeness", in
which case Jeholornis could be the closest, but a cladogram wouldn't
show that (unless its branches are somehow weighted). And, more
importantly, this type of "closeness" would probably not be a good
predictor of traits.

Instead, what does the bracketing tell us? It says that Archie is
outside a clade (Clade(Jeholornis + Aves)) that has a reversed hallux,
and the further outgroups lack a reversed hallux. So phylogenetic
bracketing tells us nothing. The only thing we can do is look at the
fossil itself.

(If the phylogeny of Prieto-Marquez & al. actually shows a clade that
includes Archaeopteryx and Jeholornis but not Aves, then everything I
said is wrong and please ignore it.)

> Archaeopteryx may have been less 'roosty' than its cousin Jeholornis, but 
> this may most likely be a reversal

Based on what?

> and there was pretty clearly a long term trend toward acquiring arboreal 
> features within the Avialae.

Sure, but Archie is near the very beginning of Eumaniraptora. It need
not be a part of this trend.

Trends have to start somewhere but there is never any guarantee that
it's at the very beginning of the branch.

-- 
T. Michael Keesey
http://tmkeesey.net/