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Re: Ah ha! That's where therizinosaurs came from
On 8/15/2011 2:12 PM, Mike Keesey wrote:
My resources are limited, but what I can glean indicates that the geo-record
> shows powered flight as pre-dating the knee-walking pelvic limb condition
> seen in modern birds, ratites (and phorusracoids, btw) included.
Interesting observation. Are there other taxa with long legs and short
No bipedals that I know of -- noting again that my resources are limited.
Also, didn't flight develop before the appearance of short
femora in the avian line?
Yes, that was my thought -- actually what I thought I said, femoral
shortness seemingly associated 100% w/ knee-walking :).
That said, estimating the ratio: femoral length /(tibiotarsusal +
tarsometatarsal length) -- yields a number line that has non-avian
bipeds on one end, and modern birds on the other.
Assuming the bird pelvic leg condition is the result of optimization for
powered flight (launch-leaping and short tail) predicts that there will
be a number such that all modern birds will be on one side, and all
other theropods on the other, and possibly even a continuum of birdiness.
(Even assuming a conservatively late
appearance of flight, around Pygostylia rather than Eumaniraptora.)
Which 'anatomically' rules out a basal non-phlight condition in ratites
in my view (not that anyone here seriously advances that idea -- but the
question was raised by Jason as a sidebar).