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Re: FW: Microraptor hanqingi, new species from China.



Entire post repeated for context in this fast-moving thread:

Am 25.05.2012 23:38, schrieb Jason Brougham:

 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 Jeholornis and more so, as well as longer and
 stronger, by Changchengornis. 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.

Don't equate "gripping" with "gripping branches". As I mentioned, I'm thinking of the "stability flapping" paper here.

Adaptations to gripping prey, if they went beyond those seen in *Deinonychus* or *Velociraptor*, may have been enough to make it possible to grip branches, and once that happened, selection for better (more energy-efficient) gripping of branches may have led to the partially and then fully reversed hallux of *Confuciusornis*, *Changchengornis* and "finally" Ornithothoraces. All this should be testable -- the "may have been enough" part is a matter of mechanics.

(Scare quotes because *C.* and *C.* are the same age as plenty of enanti- and euornitheans; there's no direct evidence that their condition[s] came first, although parsimony does suggest so.)

Whether running with leg wings was possible depends on the orientation and (presence or absence of) mobility of the feathers, which is difficult to reconstruct from flattened fossils, so I try not to have an opinion about this point.

I have read the rest of this discussion; I have stuff to look up (later) before writing more.