Re: 11th specimen of Archaeopteryx

[Jason Brougham <jaseb@amnh.org>]

On Nov 2, 2011, at 2:27 AM, Scott Hartman wrote:
> 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 is true in the case of the new Xiaotingia cladogram (Xu et al. 2011), 
because Archaeopteryx moves into its own clade with Xiaotingia and Anchiornis, 
and Archaeopteryx splits with Jeholornis which stays in Avialae. This 
Archaeopteryx clade then really does look like a bunch of small but terrestrial 
feathered theropods.

But the other recent cladograms and, importantly, the ones that include a 
larger number of basal avialans (like the crucial but underrated Zhongornis), 
suggest that Archaeopteryx was just one step below the node where adaptations 
to climbing and perching started to accumulate. It is possible that 
Archaeopteryx itself had not yet begun to involve trees in its biology, or that 
it secondarily abandoned them. Still, as I say, some animal may have and 
perhaps even must have begun to climb into trees before it had the anatomical 
adaptations to do so very well, and this may have set up the selection pressure 
that drove those adaptations, and Archaeopteryx is a perfectly good candidate 
to be that animal. The earliest utility of climbing into trees may have been in 
roosting, because foraging in trees may require better adaptations to be 
efficient (though Jeholornis somehow did swallow dozens of gymnospem seeds).

As I mentioned earlier the newest paper (Prieto-Marquez, Bolortsetseg, and 
Horner , 2011) places the Archaeopteryx as a sister taxon to Jeholornis. 
Whether Jeholornis had a reversed hallux or not is apparently a  matter of 
debate, but it seems to at least be in an intermediate position, at least 
partly reversed. In this topology, then, the probability that the Archaeopteryx 
lineage faced some selective pressure for climbing seems to be high.

The relationships of basal avialans are now in turmoil, thanks to Xiaotingia, 
so it may be some time before things settle down enough for us to form a  
consensus on the phylogenetic pattern.