[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



>>  
>> 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. 
> 
>How speedy? 

=========================================

Hatchling to sexual maturity in 1 year or less, for most monitor species. I 
have 6 months for a chameleon species. As for the pythons, Burmese go from 22" 
hatchlings to 9 ft individuals in a year's time. Whether they hit sexual 
maturity at that point; I'm not sure. I might be able to grab some more info on 
this tomorrow (assuming the library stocks the journal: Evolution). 

___________________________________________

>> Then there are squid, which have one of the fastest  
>> growth rates of any living creature studied. 
> 
>Sounds interesting. But then they don't have hard parts to build up (apart 
>from the beak), nor a lot of muscles (they don't need to support their 
>weight), so their growth should be cheaper than that of a terrestrial 
>vertebrate. 
>       Are the fast-growing fish as well ossified as the slow-growing 
>ones? 

================================================

No mention on ossification. I'd imagine, but I can't verify it. The study 
looked more at the trade-offs in cost between fast growth and maneuverability. 
The end result was something along the lines of: "It's harder to move fast, 
when one has a full stomach." 

_________________________________________________

 
>> >[...] an elephant still needs big  
>> >ears, despite having lower metabolic rates per mass than a mouse.  
>>  
>> ============================================== 
>>  
>> 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 
> 
>Is that a fact? I knew about e. g. sea cows, but elephants? 
================================================

According to Spotila:

"...in order to maintain a constant body temp of 37 [degrees] C. ... A large 
ectotherm (100 cm body diameter) would need a net heat production of less than 
0.1 cal cm^-2 min^-1... This is similar to the metabolic heat production of 
elephants."
 
________________________________________________

>> the result 
>> of a requirement for this MR, or an evolutionary holdover (i.e.  
>> automatic endothermy is hard to get rid of once evolved)? 
> 
>Then who says endothermy isn't plesiomorphic for dinosaurs? 

==================================

For one, I don't see any evidence to suggest it. Dinosaurs showed a variety of 
adaptations for increased aerobic exercise, but these are adaptations seen in 
other archosaurs, and other reptiles,before, during and after the dino reign 
(including present day).

_____________________________________
 
>>  
>> ========================================= 
>>  
>> 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 
> 
>Fish swim. Swimming is a lot cheaper than walking, as GSP quantified (any 
>movement of the body moves you through water; a leatherback turtle's 
>metabolism could not sustain any reasonable walking speed).

===========================================

I wonder if a whale's would? 

Either way, the "swimming is cheaper" argument only goes so far. Not all fish 
are endurance champions. In fact, it would seem that few marine organisms are. 
Of those marine creatures that are good at keeping up a fast speed for a long 
time, the results are achieved through means independent of "warm" and 
"cold-bloodedness." Instead it is based on how much O2 one can shove into the 
system (and, yes, how much CO2 one can shove out). From what I have read, this 
"rule of thumb" is maintained regardless of whether one is on land, air, or 
water.

________________________________________________

Insects are 
>tachyaerobic, and at the same (high) speed flying is more efficient than 
>walking. 

=============================================

Yes, tachyaerobic, but still bradymetabolic (i.e. it's not thermophysiology 
that is the limiting factor in endurance).

_____________________________________________
 
>> As for brooding, I could bring up those pythons again. 
> 
>They are part of the argument that constant high metabolism is good for 
>brooding. :-) 

=============================================

But, does it make a lot of evolutionary "sense" to evolve a constantly high 
metabolism, for the "purpose" of keeping eggs warm during a certain, limited, 
time of the year? Wouldn't it just be cheaper to have a high metabolism for 
those parts of the year?

Side note: anyone know why skunk cabbage evolved endothermy?

______________________________________________

----------------------------------------------- 
>> Is not gigantothermy anything more than just scaled up inertial 
>> homeothermy? 
> 
>Sure. Which is why I mentioned it even though you didn't mention the word. 
>Anyway, the real point of this is that gigantothermy doesn't give you 
>chemical energy, while endothermy does, and for muscle contraction you 
>need ATP. 

=================================================

Hold on a minute. Feel free to refresh my memory here, but I never remember 
reading on endothermy giving any animal (or plant) chemical energy. In fact, 
this is practically the antithesis of what so many metabolic studies have 
shown. It costs a lot of energy to be a consistent endotherm. Even facultative 
critters like honeybees, pay for it in terms of nectar requirements. 

___________________________________________________
 
>> 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. 
> 
>Is that about endurance? Or just about how high their exercise metabolism 
>can rise and how good their remarkable respiratory system is (in short, 
>they aren't really bradyaerobic)? 

==================================================

I almost wonder if we are debating two separate things here. I'm certainly not 
arguing that dinosaurs were bradyaerobic. I simply think they were 
bradymetabolic, or eurymetabolic; if you will (i.e. they had a variable MR, not 
a slow MR, or a consistently high MR). 

Tachyaerobic lifestyles are certainly possible on a bradymetabolic energy 
budget. As you mentioned, varanids probably aren't bradyaerobic (in fact, 
Scleroglossa itself, seems to have many species that show increased aerobic 
capacity), yet they are bradymetabolic.

As for the study, it did show aerobic endurance comparable to mammals. The end 
result of that study showed that varanids have aerobic scopes that increase 
with temperature, and that increase with size.

I have another study that shows, essentially, the same results. It was done on 
57 lizard species, spanning most, if not all, major families. Both studies show 
results that are almost counterintuitive for reptiles. Certainly for fans of 
Bakker's "heresies." Of course, there have been quite a lot of studies on 
reptilian endurance since then (even before then, but I won't get into that).


Jura

======================================================

"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