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Re: the reason I asked about maniraptor limbs
Sam Barnett writes:
If a juvenile bird that has not yet mastered
its own aerodynamic abilities runs the risk of dying every time a
potential predator wanders past, what hope do creatures of the same
basic body plan, but with little or no aerodynamic abilities, have?
Every single volant species has individuals that occasionally die an
accidental death (juvenile or otherwise). Then again, even the most
accomplished of arborial animals sometimes plummet to their doom, and the
most agile of terrestrial runners occasionally trip and break a leg. It's a
scientific principle known as 's**t happens'.
An adult maniraptor should not be as ungainly as a juvenile bird, and
less likely to take stupid risks. This still leaves little saving
graces when things go wrong, and early climbing would go wrong unless
aerodynamic grace preceded climbing as a result of some other function
of ground running life.
Not as long as the benefits of climbing outweighed the occasional accident.
Antelope still try to outrun predators despite the chance of a fatal trip,
and spider monkeys still live in trees despite the occasional plummet of
doom. It's better to escape 100 predators (or get to 100 food items) by
climbing - and risking that 1 in 100 fatal accident - than to not climb at
all and either get eaten or starve to death.
Do we have the big maniraptor hind claw to thank for the development
of skilled climbing? One thing our bird's earlier climbing ancestors
had that their contemporaries do not, is the famous crampon-like toe
and its stabbing action.
The dromaeosaur second toe claw is better designed for piercing than
grasping, at least in the larger-bodied species. The claws of climbers tend
to be round or oval in cross section, so they don't pierce too far into
whatever they're trying to climb, and no doubt to help strengthen the claw
against sheering forces. Dromaeosaur pedal claws are narrow and blade-like
in cross section. I don't seem them as having been very useful in climbing
trees - although they could have been useful in scaling something softer and
fleshier (and doing incidental damage in the process).
Of course, we're trying to use dromaeosaurs that post-date Archaeopteryx as
analogues for its pre-volant ancestor. Later dromaeosaurs were probably as
derived from archae's ancestor as archae's itself was. What we really need
are some good pre-Late-Jurassic maniraptor fossils.
GIS / Archaeologist http://www.geocities.com/dannsdinosaurs
Melbourne, Australia http://heretichides.soffiles.com