Re: the reason I asked about maniraptor limbs

[Dann Pigdon <dannj@alphalink.com.au>]

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. 

___________________________________________________________________ 

Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
___________________________________________________________________