Re: Not dinosaurs but chondrichthyans

["Tim Williams" <twilliams_alpha@hotmail.com>]

Colin McHenry wrote:

> but anything that gets people to question the old chestnut about sharks 
> being some relict primitive group is good in my book. I used to emphasise 
> to students that white sharks are late model, highly evolved, warm blooded, 
> live young bearing, mammal eating machines). The standard doco line about 
> sharks being some relict group of monsters is absurd.

I couldn't agree more.  People sometimes assume that the record of 'sharks' 
is as old as chondrichthyans, when in reality the first known modern sharks 
(= crown group Neoselachii) appear only in the Mesozoic.

White sharks (and some other lamniform sharks) display something called 
"regional endothermy", which I've never fully understood.  It does allow 
their body temperature to rise above that of the ambient water temperature.

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