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Re: Fwd: Re: New Study, T rex Could've Been A Scavenger



> 
>> Regardless of what Bakker, Paula and others have stated on the matter, 
>> there is still no reason for _T.rex_ to not have been a bradymetabolic 
>> "good reptile." 

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Side note: though I'm sure it is obvous, I meant to say Paul, not Paula. Bloody 
typos!

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Work by Nicholas Hotton, 
>> James Farlow, James Spotila, Walter Auffenberg (to a lesser extent) 
>> and others, have shown that a large bradymetabolic 
>> animal can do just as well as a large tachymetabolic one. 
> 
>"Large" being the teeny tiny Komodo monitor. 

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Large enough to put it on par with some of the large cats (and canids); all of 
which have been scaled up to be compared with dinosaurs before. Admittedly, we 
don't have anything larger than a saltwater croc today, for reptiles, but we 
don't do much better among mammals either. Especially for the predaceous ones.

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And I haven't read a rebuttal 
>to HP GSP's idea that bradymetabolic animals are simply incapable of 
>growing as fast as big dinosaurs did (remember our last discussion). 

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Considering the amount of studies done on non-avian/mammalian growth rates, 
this seems to be more of an assumption on GSP's case. I did give mention to the 
speedy growth seen in certain pythons and monitors. Then there are squid, which 
have one of the fastest growth rates of any living creature studied. There is 
also the disparity in growth rates seen in individuals from different locales. 
Reasons behind this seem to be both environmentally dependent (food 
availability and temp stability), and genetic.

A prime (apparent) genetic example that comes to mind, is the recent research 
done on Atlantic silverside fish. When comparing individuals from two separate 
locales (Nova Scotia and North Carolina), it was discovered that the Nova 
Scotian animals grew twice as fast with the same amount of food, than their NC 
brethren. There are plenty of questions about bradymetabolic animal growth 
patterns (growth patterns in general) that could use answering. 

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>> Some studies even show a general trend towards  
>> bradymetabolism in larger animals 
> 
>True, but not true enough -- which is why an elephant still needs big 
>ears, despite having lower metabolic rates per mass than a mouse. 

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Ah, but as Spotila (1980) mentioned on this; is the fact that an elephant's MR 
is only slightly higher than a reptile of equivalent size the result of a 
requirement for this MR, or an evolutionary holdover (i.e. automatic endothermy 
is hard to get rid of once evolved)?

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>> (which makes sense, if the entire point  
>> of being tachymetabolic is just to keep 
>> warm).  
> 
>Well, it isn't. Who said it was? 

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Bakker, Ostrom and many others in passing. I'm sure you've come across it 
occasionally. You know, the advantages of having a constant thermal stability 
etc.

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What exactly the point is is still not 
>clear...

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Agreed.

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..., but endurance looks like a good idea, as does brooding. 

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As I mentioned previously, endurance has a false correlation to 
tachymetabolism. Yeah, if one compares all extant reptiles to all extant 
mammals and birds, then one should get a noted correlation between 
tachymetabolism and increased endurance, but if one adds fish and insects into 
the mix (especially those speedy swordfish, tuna and laminiformes), then your 
correlation is going to get shot (or, at least, extremely messy). One would 
probably end up with a strong correlation to small size and endurance (or 
flight and endurance). Aerobic capacity seems to have a more direct link with 
anatomy (insect trachea, non-sigmoidal movement, alveolar lungs, air sacs, 
diaphragms and gular pumps).

As for brooding, I could bring up those pythons again.

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>       Apart from that gigantothermy doesn't work for pretty much 
>anything with a shape different from a sea turtle's. 

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Is not gigantothermy anything more than just scaled up inertial homeothermy? We 
have plenty of bradymetabolic animals alive today that use inertial homeothermy.

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>> and statements about a lack of aerobic potential make no sense 
>> either (carrier's constraint in many modern reptiles is do to anatomy,  
>> not thermophysiology).  
> 
>For how long can a bipedal lizard run? Or a baby croc gallop? 

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I'm not aware of endurance tests in either group, though consensus seems to be 
that they don't run for very long (the latter especially, as it is only a means 
of escape). 

I do have aerobic endurance info on varanids though (big surprise >:)

Studies on varanids by Bennet (1972) showed that at mammalian body temps, 
aerobic scope was essentially the same. They incur oxygen date no faster than 
mammals, and repay it just about as quickly.

Other than that, I'm sure I could come up with some refs on marlins and bees 
that would probably show the same kind of thing.

Jura

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"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." 
- Alfred S. Romer  Osteology of the Reptiles

http://reptilis.net