Re: Regarding Spinosaurus

[Jura <archosaur@reptilis.net>]

--- "Adam Britton" <abritton@wmi.com.au> wrote:
>I can immediately think of two than may qualify. Green iguanas extend >their 
>dewlap when they are below preferred body temperature and >exposed to radiant 
>heat. While there may be some social function in >doing this, it's clearly 
>increasing surface area. However, I don't >know whether this provides 
>significant benefit, nor whether it's been >looked at experimentally. 

+++++++++++++++++++++++

Not sure, can't say that I've seen this in my iguana though. I have seen gaping 
and dewlap extension in overheated iguanas. Same for most other lizard species. 
Sometimes even panting (varanids).

I probably should have better clarified what I meant by large reptile. By 
modern standards a green iguana is a large reptile (with a 7ft max they're 
certainly nothing to sneeze at), but my main examples were revolving around 
Komodo dragons, giant tortoises and crocodylians.  

___________________________________________


>What has been tested, though, is the heat-acquiring potential of the >dorsal 
>osteoderms of crocodilians. While they are not a significant >extension of 
>their back in terms of surface area, they do function as >solar panels, being 
>infused with blood vessels that transport warm >blood to key parts of the body 
>more quickly.

++++++++++++++++++++++++++++

I remember reading that. This was later used as possible examples of 
thermoregulation in dinosaurs; particularly stegosaurs and whichever ornithopod 
had those strange "mini-volcano" scutes.

Still in crocs, it was more of an exaption (surely it's considered correct 
context now right :) of the present since _Protosuchus_ dorsal scutes and less 
the evolution of an entirely new structure.

____________________________ 

>Yes, but tropical species live in an environment which is typically    
>>(during daylight hours at least) at least as warm as preferred body 
>>temperature.
>Hence the relative abundance of nocturnal reptiles in the tropics. >During the 
>day, most tropical reptiles spend far more time avoiding >overheating during 
>daylight hours, rather than the other way around.
>
>Adam Britton


++++++++++++++++++++

True enough and a good point. Cooling down is far harder for reptiles than 
warming up, hence any thermoregulatory adaptation seen, would probably be more 
related to dumping excess heat, rather than acquiring it.

As for the environments, barring very few exceptions, dinosaurs were tropical 
reptiles.

Anyway the long and the short of this post is that having a sail that is used 
as a heat dump, does not automatically mean the animal is "warm-blooded" as the 
"cold-bloods" are just as likely to do the same.

Jura

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