Re: 11th specimen of Archaeopteryx

[Jason Brougham <jaseb@amnh.org>]

On Nov 2, 2011, at 1:49 AM, Scott Hartman wrote:

> 
> The thing about roosting is it requires that the birds be able to land
> at a slower speed without stalling.  There's not evidence that
> Archaeopteryx could do this, 

That is how dedicated ground foraging birds like Blue Herons roost, but this 
behavior is not required to roost. Kagus and trukeys climb up the trunks of 
trees, they don't alight in them. As others have documented, almost any animal 
that can walk can get into trees this way, even if they have no perching 
specializations at all (turtles, goats).

>  I think the
> only reason Archaeopteryx even shows up in these discussions is due to
> the mistake of referring to it as a "bird", not because anything in
> its anatomy supports it.


No, sir. The reason is that it is an animal with a very small body size, which 
lived in the Jurassic right before the origin of birds, which for decades (more 
than a century) was the most basal known avialan, and because of the 
tantalizing possibility that Archaeopteryx may retain many features of the 
ancestor of all birds, or else that it is that ancestor (Witmer, 2002, "The 
Debate on Avian Ancestry", discussed this possibility with inspiring open 
mindedness). Many basal birds, taking Sapeornis as just one example, are 
interpreted as having arboreal adaptations.

> 
> 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.

Turner(2007) demonstrated that the ancestral paravian had an estimated mass 
between 600 grams and 4.2 kilos, which is well within the body mass range of 
birds that roost in trees. The Oosh deinonychosaur is among the most basal and 
absolutely tiny, in agreement with Turner. The Oosh paper also, interestingly, 
seemingly failed to recover a monophyletic Dromaeosauria.

So immediately at the base of Avialae we have the Archaeopteryx/Jeholornis 
node, one of which has the most basal known reversed hallux. Next up we have 
Sapeornis which may have had the toe claw curvature of tree foraging birds. 
After that we go up to Gansus and cuckoos.

Archaeopteryx may have been less 'roosty' than its cousin Jeholornis, but this 
may most likely be a reversal, and there was pretty clearly a long term trend 
toward acquiring arboreal features within the Avialae. There were also numerous 
secondary reversions to terrestriality. Perhaps Archaeopteryx was to Jeholornis 
within their clade what Meleagris is to Penelope within the Galliformes. 
Namely, a more terrestrial member of a tree roosting order.