[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: "Flight theory has legs"

Scott Hartman <DinoBoyGraphics@aol.com> wrote:

Ok, so the results are preliminary and need to be confirmed, perhaps further study will show otherwise, but common [sic] guys, you are really special pleading to shoe-horn the current results into the trees-down (or trees-sideways) idea of flight origins.

I would say that the morphologies of _Microraptor_ and _Cryptovolans_ require very little "special pleading" to be shoehorned into (a) an arboreal or (b) a gliding ecomorphology. What's the difficulty? the fit appears to be very comfortable.

Dinobirds leaping from branch to branch would be in dire need of pedal claws for grasping the branches the landed on.

Excuse me, but never once did I say that arboreal/scansorial maniraptorans leaped from tree to tree, or from branch to branch. The evidence favors descents from trees to the ground on the part of small-bodied, long-feathered maniraptorans.

The condition is made worse because their long columnar limbs put their center of gravity further away from the branch, decreasing mechanical advantage for stopping their momentum.

Please show me your calculations for estimating the center of mass (CM) in Mesozoic maniraptorans.

I would also add that, as demonstrated by Gatesy and others, the most basal birds retain primitively long hindlimbs that are strikingly dromaeosaurid-like in their proportions. This includes _Sinornis_, which had a highly specialized perching pes.

Archaeopteryx and other dinobirds may not have even had a fully retroverted hallux, and they certainly did not have the large flexor tubercles and curved pedal phlanges needed for such scansoriality.

Well, perhaps the fact that they had arms and hands to help them climb alleviated the need for a specialized grasping pes. _Archaeopteryx_ (at least) does appear to have had a fully retroverted hallux.

I know that a trees-down origin is more intuitive,

Intuitive, schmuintitive. A "trees-down" origin of birds is corroborated by anatomical and phylogenetic evidence, and is at least as strong as the "ground-up" scenario. BTW, as has been argued many times on this very list (by myself, among others), there's no reason why these two scenarios ("ground-up" vs "trees-down") should be considered mutually exclusive.

and I've convinced that both bats and pterosaurs evolved flight in an arboreal context,

Intuiton is all we have in the case of pterosaurs and bats. There are no known (or recognized) fossils of non-volant sister taxa to either the Chiroptera and Pterosauria.

but dinobirds are very different.

Yes, they have a fossil record - which includes scansorial, aerial taxa such as _Microraptor_.


MSN 8 with e-mail virus protection service: 2 months FREE* http://join.msn.com/?page=features/virus