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Re: New Feathered Dinosaur





 


----- Original Message -----
From: Ken Kinman
Sent: Wednesday, May 02, 2001 5:56 PM
To: dinosaur@usc.edu
Subject: Re: New Feathered Dinosaur

     Looking at croc ancestors, and early crocs, their skeletal proportions often seem to be very cursorial, and they seem to have had fully upright posture. These are classic signs of endothermy, but modern crocs are fully ectothermic. This cannot simply be explained as a lowering of metabolic rate, as endothermy in birds and mammals is believed to have a simple genetic basis, 'leaky cell' endothermy is thought to be caused by a mutation in a gene concerned with forming Na+/K+ channels in cell membranes. The membranes then become prone to losing K+ to the tissue fliud along their concentration gradient, and gaining Na+ ions. Animals maintain high K+ and low Na+ concentrations in their cells against the concentration gradient, and therefore the Na+/K+ pumps of endotherms have to work harder than those of ectotherms, this reqiures more ATP and therefore a higher rate of respiration, which produces heat as a side effect. This seems to have been selected for even though it requires more energy, as the benefits of endothermy have outweighed the energy costs. If this was not the case in crocs when they became aquatic, then they could have lost endothermic metabolism and retained endothermic charecteristics like a four chambered heart. This would explain to some extent fossils like the Australian hooved running croc, which could have still been endothermic (and insulated). Or I may be spouting rubbish:)

Thanks for tolerating my mad rantings

Patrick

 

 

 

 


Allan,
    Yes, and I believe Larry and Dinogeorge might call such common ancestor
a dino-bird (although I'm not sure Dinogeorge is all that keen on the
pterosaur connection).  The similarities may be convergent, but I think it
is well worth looking into the possibility that they are not convergent.
     Who knows, maybe even some of the early ancestors of crocs had fuzzy
little babies (but lost the fuzz when they turned aquatic).  Idle
speculation?---perhaps.
                    -----Ken Kinman
*******************************************************
>From: "Allan Smith" <fossilsmith@hotmail.com>
>Reply-To: fossilsmith@hotmail.com
>To: dinosaur@usc.edu
>Subject: Re: New Feathered Dinosaur
>Date: Wed, 02 May 2001 16:29:30
>
>Ok, just for the sake of argument, lets say that the two structures are
>extremely similar in structure and function, could'nt it be argued that the
>origin of "dinofuzz" came from a common ancestor shared by both theropods
>and pterosaurs? Assuming of course that all pterosaurs had this "hairlike"
>covering.
>
>Allan Smith
>Fossilsmith Studios
>
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