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Re: Phytodinosauria status - digit loss.
In response to my :
<< Digit loss, at least in digit 1 and 5, would appear to go with shortened
center fingers and flexing the ankle or wrist front to back, allowing a
vertical gait. If you contract the muscles and tendons leading to the
fingers at the same time and these tendons are lower than the wrist/ ankle
joint centerline, you should get a front to back rotation, not side to side
<Yes, but digit 1 was >not< lost in theropods; digits 4 and 5 were. These
would have been on the back side of the wing, where it needs to taper in
order to generate lift. And center fingers were elongated in most theropods.
Regardless, the loss / reduction of digit V and the first metacarpal being
offset could be explained as a result of a vertical (quadrupedal on occasion)
gait in its very early stages, the reduction of the IV digit can not.
However, climbing does not explain it either. Getting rid of or reducing the
outer toes reduces the number of hooks and the ability to wrap around a
branch when climbing with the arms extended. Their loss/ reduction would
suggests to me that earlier dinosaurs were less likely to be tree dwellers
than their ancestors. Add to that the vertical pubis and you have a harder
time holding on. The rearward pubis of later theropods, millions of years
after flight evolved can be explained many ways, none that I know suggesting
that it occured before flight was obtained.
Gregory Paul, in PDW, page 212, shows the feathers attached to digit II.
If digits IV and V got in the way, why wouldn't digit III. Probably because
it was under the feathers where it could still grab, as would have the other
Even so, if flight occured early, as George implies, losing digit IV would
make sense. 4 claws are not better for grabbing than 3 but 3 are better than
2. Of course this would true of non fliers also.
Lastly, lift is not generated by a taper! It is generated by forcing air
down (with feathers in the dinosaur / bird case. An airfoil shape generally
allows the most lift to the least drag and allows you to use equations to
calculate it. Look in last months National Geographic for more information
on lift and forcing air down. Again, if flight started first, a reduction in
digit IV would be logical.
Longer center fingers in theropods is seen in theropods currently
considered as closer related to birds, not earlier theropods (based on my
limited knowledge). After early dinosaurs became bipedal, there was no need
for short fingers until weight forced a quadrupedal gait.
As an aside, do we know if early fliers had layers of feathers,
sucsessively shorter on top or do we assume this because birds are this way?
I can not tell by pictures.