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Re: Lizard study asks: Why go bipedal?



Jura writes:

Recently announced paper from Clemente et al, decides to tackle the "why do so many lizards run bipedally" issue.

Clemente, C.J., Withers, P.C., Thompson, G., Lloyd, D. 2008. Why Go Bipedal? Locomotion and Morphology in Australian Agamid Lizards.J. Exp. Bio. 211: 2058-2065

Available here:

http://jeb.biologists.org/cgi/content/abstract/211/13/2058

... All is not perfect though as there are some gripes to be had with the 
paper. For one, the authours mention other times in which vertebrates have 
evolved bipedalism. They mention dinosaurs, birds, kangaroos, and primates. 
They argue that freeing up of the forelimbs might allow for the their use in 
alternate ways...
Furthermore, what the heck do kangaroos get out of having their forelimbs freed 
up? I've seen wallabies use their forearms to help hold food, but kangaroos in 
general just seem to use them for standing.

Macropods forelimbs are used for:


* Low-speed locomotion, via a pentapedal gait (the tail is used as a fifth limb)
* Combat, whereby males wrestle with each other to compete for females. I've heard that kicking out at each other is a last resort, and often initiated by the losing male.
* Temperature regulation, by licking the forelimbs and relying on evaporation to cool the blood flowing through them.


I doubt that having the forelimbs free is necessary for the last two. It would seem that high-speed bipedalism in macropods has little to do with freeing the forelimbs for other purposes, and more to do with a more efficient locomotion method in a continent where poor soils and low-quality plants tend to select for energy-efficiency. Hopping gaits have evolved independantly in rodents as well, usually in environments were energy efficiency is also highly selected for (mostly deserts).

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Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com
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