Re: questions about the Odontochelys study

[Mike Habib <habib@jhmi.edu>]

Tim Williams wrote:
> With the disclaimer that I don't know all that much about turtles...  
> I do know that the snapping turtle and mata mata are ambush  
> predators, so protecting the underside may not be so important.  Or  
> at least, belly armor (plastron) is not as important as it is to  
> aquatic turtles that spend more of their time swimming in the water  
> column.  In other words, if such aquatic ambush predators spend much  
> of their time motionless, with their bellies close to the sediments  
> underneath, then their bellies are not as vulnerable to attacks from  
> below - hence the secondarily reduced plastron.

I think you're more or less right on the money.  In fact, mata-matas  
and alligator snappers both rarely swim in the water column even while  
moving about; they move along largely by punting, and so they are  
almost always near the substrate.  The reduced plastron is therefore  
of limited cost, while it provides substantial benefits in allowing a  
transiently higher "walking" gait for punting along the bottom -  
improved mobility for marginal cost.  Common snappers free swim more  
often, but still spend large amounts of time bottom resting, and have  
the added advantage of intense offensive weaponry.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu