Re: Regarding Spinosaurus

[Jura <archosaur@reptilis.net>]

Fam Jansma wrote:

>The sail on the back of Spinosaurus could be clue to the >coolbloodiness of 
>this critter.

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

Probably not; there are extant "cold-blooded" reptiles today with sails and 
none of them use their sails for any thermoregulatory boost (they can't as they 
all live in environments that aren't very conducive to solar heating). In all 
cases, sexual selection seems to be their big reason to evolve. Furthermore all 
large reptiles lack any form of heat acquiring device. Since they are so large, 
they retain the heat acquired during activity and most (e.g. Komodo dragons and 
large crocodiles) rarely drop more than a degree or two throughout the day. 
They are essentially "warm-blooded" at this point.

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.

______________________


>Look at present reptiles, they need to 
>warm themselves in the morning to "activate" themselves in the mrning >and 
>because of their colbloodiness, they need less food. 

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

Well kinda. At small sizes a bradymetabolic ("cold-blooded" if I must) animal 
needs less food than a tachymetabolic one, at larger sizes this disparity 
decreases and eventually leads to little or no disparity at all (see Farlow et 
al's papers in the book: A Cold Look at the Warm-Blooded Dinosaurs).

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.

On the flip side, most mammals and birds need to eat as much as they can as 
often as they can in order to keep activated.

Sorry, I just hate the wording of these things at times. 


_____________________

>A sail would surely have speeded up the process so the Spinosaurus was able to 
>hunt 
>fish in the morning. Fish are a little numb in the morning, making >them 
>easier to catch and so supplying the Spino every morning with a >scaly 
>breakfast. If the Spinosaurus was coldblooded, it also needed >less fish to 
>eat every day, so it wouldn't have needed a bigfish->supply.

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

Fish are functionally (or is that environmentally?) homeothermic due to the 
thermal consistency of water, which might explain why I've never seen a logey 
(sp?) or "numb" fish in the morning or evening. 

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.



As a side note, I've always been partial to the idea that _Spinosaurus_ evolved 
that large sail in order to mimic the _Ouranosaurus_ of the time and sneak in 
close to them. It's the ultimate "wolf in sheep's clothing" scenario. It's also 
the ultimate in speculation, but at least it makes for a neat artistic 
scenario...well, as long as one is willing to extend the length of time for 
either _Ouranosaurus_ or _Spinosaurus_.

Jura

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