Re: What is a Dinosaur? and semilunate carpal

["David Marjanovic" <david.marjanovic@gmx.at>]

> "Stable hands" are certainly not required for predation--they are probably
a
> >hindrance< to predation--otherwise there would be more predators with
> "stable hands."

Wait a minute. There have _never_ been any _bipedal_ predators other than
theropods, most or all of which have (had) very stable hands.

> But "stable wings" >are< required for the kind of flying that
> birds do; it would be positively selected for in the evolution of arboreal
> dinosaurs, and all modern flying birds retain them. So it is more likely
that
> "stable wings" would develop for flying and then would become exapted by a
> flightless predatory descendant than that "stable hands" would develop for
> predation in a flightless predator and then would become exapted for
flight.

It is even more likely that you need stable hands _before_ you _begin_ to
fly (hmmm, I haven't tried, but I can't really imagine flying with anything
like my wrists).

> In the standard theory of avian flight, "stable hands" is one of those
> characters that arose by chance in predatory dinosaurs and then
miraculously
> found a use, along with all those other characters that also arose by
chance
> for various other reasons, in flying. Sorry, I don't buy it (and in fact I
> think it is ridiculous), >especially< since there is a very
straightforward,
> reasonable explanation that doesn't involve any more random chance than
> necessary for theropod "stable hands" in BCF.

May sound strange, but IMHO it is exactly the other way round:

In BCF birds (sensu BCF) begin to fly, then evolve stable wrists, and in the
meantime they have flown by magic? Or by means of _enormous_ muscles on
their forearms?
        In the "standard theory" (judging from this list it consists of
hundreds of competing hypotheses) there is a function that can be performed
without stiff wrists but works _better_ with stiff ones, so when stiff
wrists evolve -- of course by chance, as mutations happen -- they bring a
selective advantage.
        This is, BTW, very similar to the explanation of why digits evolved:
If you hunt like a pike in thick undergrowth, you obviously don't need
digits, as shown by the pikes, but if you've done some strange things with
your hox genes and have digits, it certainly helps. And ready is
*Acanthostega*. Now turn this into a bottom-water hunter, where there isn't
enough oxygen in the water so it loses its gills and the lower part of its
tail fin, and you have *Ichthyostega*. One last mutation to distort its
hindlegs, and _now_ -- no earlier -- it can walk on land.