RE: Microraptor hanqingi, new species from China.

[Jason Brougham <jaseb@amnh.org>]

Sorry I just sort of blurted this out without thinking it through very 
carefully, so I welcome your help. 

In a hypothetical, strictly ground - up, ancestor of Avialae, wouldn't we 
expect the feet and legs to completely retain their ancestral form? Only when 
we get to powered flight will the little dickens' be able to drop down onto 
trees, and only then can they start adapting to branch gripping. 

But the actual sequence is that we get wings on arms and legs simultaneous with 
the descending Mt I. Then we move into Avialae, then we get partial reversal of 
hallux coincident with incipient improvements in the pectoral girdle 
(Jeholornis). Ultimately we get derived flight apparatus and fully reversed 
hallux.

OK, to improve on this we need to look at all known fossil taxa and see if 
there is a signal. Do the changes in leg and foot anatomy correlate with 
changes in flight apparatus, or precede them, or follow them, or is there no 
real signal. Does that work for testability for anybody?

With respect to anyone who feels strongly that basal paravians were highly 
arboreal, the Glen and Bennett 2007 paper and Hopson 2001 paper, and a few 
others, persuaded me otherwise. But I am open minded to new data if 
mathematically rigorous methods prove otherwise.

________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Jason 
Brougham [jaseb@amnh.org]
Sent: Friday, May 25, 2012 5:38 PM
To: dinosaur@usc.edu
Subject: FW: Microraptor hanqingi, new species from China.

I, for one, think that basal paravians and avialans were not highly arboreal. 
But there are at least three features that suggest that something other than 
running fast on the ground had become a new priority in the biology of basal 
paravians.

One is the very long leg wings, which Xu hypothesized were in conflict with 
fast running. This is hard to test.

Two are the longer penultimate phalanges, seen also, I believe, in Xiaotingia.

Three is the evolution of the reversed hallux. It is at least slightly reversed 
by Jeho
engornis. I do assume that this indicates that being good at gripping branches 
became important to their survival early in the evolution of the modern flight 
apparatus.

I guess then a testable prediction is that, if the forms in which incipient 
flight evolved were not using tree habitats at all (if strict ground up is 
correct), the 1st digit should begin its long sequence of adaptations AFTER the 
flight apparatus is assembled.

Instead I interpret the descent of the hallux to lie close to the other toes in 
Microraptor, and more so in Epidendrosaurus and Xiaotingia to possibly indicate 
the first steps of selection for branch walking. After these incipient stages 
there is a long and complex radiation of avialans with increasing rotation of 
the hallux.

The small body size, large wings, showy tails, feathered legs, long penultimate 
phalanges, and descending hallux of basal paravians could be seen as consistent 
with animals that were using tree habitats some of the time and adapting to 
those habitats. If the descending hallux and penultimate phalanges have nothing 
to do with branches, and small animals can run just fine with long wings on 
their legs, then this is not evidence for branch walking at all. But maybe then 
the burden lies with others to explain the very long and diverse series of 
morphological changes in Mt I.