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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
femora?

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).