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Re: Phytodinosauria status - digit loss.
Losing fingers to get out of the way of feathers, of a feathered/flying
dinosaur ancestor, does not seem to be the best explaination for their
reduction / loss.
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 outer
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
A 5 toe, lizard like alternating walking motion would appear to need the
strongest lower limb muscles attached to digits 1 and 5, contracted 1 at a
time, rotating the wrist / foot sideways in an arc. It is logical to me that
they would (or could - note heel in mammals) be the same muscles, contracted
both together, that would allow the vertical gait in the wrist and/ or ankle
while the socketed hip allowed it in the hip region. Then, over time,
muscles and tendons connected these toes, flexed only the metatarsal area
around the wrist / ankle (does that go with metatarsals fuzing to /
interlocking with each other or did that occur earlier?), leaving phantom
bones and one or more stranded toes. In addition, strengthening muscles
leading to the (shortened) inner toes would lead to better traction and a
digitigrade foot unless large size (or tree living?) occured too fast.
The idea that the vertical gait would evolve in trees is at first absurd
to me. The animal would want to keep its body near the vertical branch (no
long vertical pubis) and hands and toes would want to wrap around it. Only
one front or rear limb would be released at a time, requiring a rotation
Even so, jumping from or landing on branches in trees could possibly allow
this same front to back wrist and ankle flexing motion. Even so, you would
expect to see opposable digits (which we see slightly).
Anyway, I am sure there are problems with my reasoning but it gives an
alternative to losing / partially losing front fingers only as a means of
getting them out of the way of feathered ancestors. Losing digits to get
extra joints, and hence running speed, appears to be a common, gradual theme.
I am also trying to figure which fingers (if any or more than one) would
have been feathered in Deinonychus.
Mark "probably should have kept quiet" Shelly