Re: Regarding Spinosaurus

[Jura <archosaur@reptilis.net>]

--- "Fam Jansma" <fam.jansma@worldonline.nl> wrote:
>I don't doubt the fact that the sail was used for intimidation, but the
>sails you mean are fleshy and not supported by bone. It's also hard to >think 
>of a example of an extant reptile with a sail sticking out of >it's back 
>that's around the length of it's hindlimbs. Alright, the >scale has to be 
>altered, but when you evolve this big sail, you have >to >have a practical use 
>for it and not only for impressing other >members of your genus.

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

Actually the reptiles I was thinking of were: _Basiliscus_, _Hydrosaurus_ and 
_Chamaeleo montium_, all of which have sails supported by their extended neural 
spines, just like in the spined dinosaurs, synapsids and _Platyhystrix_. They 
might not be large animals, but they're probably the best analogue to spined 
dinos that we've got.

I do agree that a use outside of sex was probably there. Rarely does nature 
evolve a new structure that only does one thing. Still I do think that sexual 
selection was probably one of the more dominant selection pressures for its 
evolution.

_____________________________


>>Of course since sails evolved in so many different dino types at that
>>period in time (and at that latitude) I do think that it probably did >>play 
>>a thermoregulatory role. Though it was probably used more as a >>heat dump 
>>rather than as a heat capturer.

>The problem is that if a Ouranosaurus dumped it's heat, it takes some >time to 
>do so, leaving it open to attack for a hungry >Carcharodontosaurus or 
>Spinosaur. Evolution has always been about survival, not suicide.

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

I don't think it would be any more so than it would if it were using it to 
acquire its heat. Besides there would be no real reason for it to stop moving 
or being alert. 

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>>Furthermore many small tropical reptiles have developed a variety of
>>different means to avoid large thermal loss (e.g. shunting, burrowing >>and 
>>selective sleeping positions, sociality) and rarely need any real >>long 
>>"activation" period in the morning.

>Carcharodontosaurus didn't have a sail, so if he had to avoid heat->loss, he 
>dug himself in to the ground? 

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

Heh, doubtful, but it probably did gape its mouth and/or pant in order to cool 
down. Having a bunch of air sacs is a good way to keep cool as well.

______________


>Can't really say it is possible with it's
>short frontlimbs and huge size, but another question revolving about >thermal 
>regulation: if all these animals in the Sahara evolved these >sails, 
>Spinosaurus, Ouranosaurus and Rebbachisaurus, than why didn't
>Carcharodontosaurus evolved one on it's back? This is troubling me for >a 
>while and there seems to be no reason that could point into the right
>direction...

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

I don't really have an answer there. It would be interesting to figure out why 
some dinos evolved sails while other, related dinos didn't. 

_______________

>>As for spinosaurs, as I mentioned above, its size would have given it >>the 
>>same food requirements as a "warm-blooded" animal of the same >>size (how 
>>long it could go without food is another story entirely >>though) and 
>>regardless of physiology, an animal that big is going to >>have a large food 
>>supply no matter what.

>The Anaconda isn't a creature that is known for it's small size, the >largest 
>one recorded was about 12 metres, coming close to a adult >Spinosaurus. It's 
>is known that these creatures can live for several >months on the remains of 
>their last lunch, a large crocodile or >something like that.

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

Large crocodiles are also thought to be capable of lasting up to 2 years 
without food. Galapagos tortoises could last for months without food or water, 
which boded well for the hungry sailors at the time and humans can last up to 3 
weeks between meals.

But, none of us naturally goes 3 weeks between meals (barring that whole save 
the children thing). All of these are extremes and most of these animals eat a 
heck of a lot more than once a year. Many eat daily. That a _Spinosaurus_ could 
probably go for a couple months (a year maybe) between meals was probably 
possible, but I doubt it was a normal thing. Just like how the Grumeti crocs 
hardly exhibit "normal crocodile feeding behavior."

All too often with extant reptiles, the amount of time that they CAN last 
between meals, is used as their normal feeding times.


Jura 

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