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Re: [Re: DOWNY STEGOSAURS (WAS: Re: Feathers on Bloody Everything)]




> =================================
> 
> So far I have yet to see any convincing 
> evidence for deinosaur endothermy.

     And I have maintained that is a perfectly legitimate (although I
suspect incorrect) position to take.  Just make sure the majority of your
illustrations show dinos laying in the shade.


> The sitting dilophosaur was, I believe bad mud
> imprints and not feathers.

     Oh?  How do you figure?   The only mechanisms I've heard implicated
that could do what you're saying happened are flowing water or
"post-sitting" mud movement (where gravity forces the rims of the
impression to partially collapse into the imprint).  Neither seems likely
when you examine the non-feather parts of the trackway.  The feet and
"ischium" imprint don't show thes structures.  Unless a very small stream
was winding its way between the feetm and missed the "ischium" imprint,
you'd expect the proposed deformation to look similar on all parts of the
imprint.  And post-movement slumping seems unlikely because if the ground
was that wet when the impression was made, the  narrower, highersided foot
impressions should again show some evidence of slumping as well.  So
without a testible mechanism explaining how the "insulatory" impression
got there, I'd be loathe to just explain them away as "bad mud
imprints."



> _Sinosauropteryx prima_ has protofeathers and not 
> true feathers.

     Certainly true from a morphological point of view.  As others have
mentioned, phylogenetic and biochemical analysis may eventually help us
cope with the semantics of the issue.  But you don't insulate an
ectotherm.  Insulation is expensive to derive, and there would have to be
a very strong selective pressure in order for it to evolve.



> Plus early birds showing signs of ectothermy.

     This falls under the bone histology myths that have been started of
late about annuli.  Annuli are not neccesarily the same as lines of
arrested growth (LAGs).  very few of the many papers have bothered to
examine the annuli found to see if they actually where LAGs. Furthermore,
many modern endotherms also show LAG's, although not to the extent that
ectotherms do.  All a LAG is an indicator of is that the rate of growth
has changed for a period of time.  This can occur as a response to many
kinds of environmental stress, including a lower availability of food to
the organism, requiring that a smaller percentage of its diet be devoted
to growth.  Much more important is the histology of the bone inbetween.
Fibro lemellar bone is virtually unknown in wild ectotherms.  yet ALL
dinosaur bones display this bone tissue (which is indicative of rapid
growth).  LAG's are in no way unique to ectotherms (and aren't even common
in dinosaurs), so are in no way indicative of a "typical reptilian growth"
rate, as posited by Dodson et al. in their avian histology work. (in fact,
Padian gave a good talk on how dinosaur LAGs, when they are present,
differ histologically from those known in extant ectotherms, even those in
tropical environments).
     Finally, as I mentioned above, many annuli aren't even LAGs. Apparent
stops in growth can occur when parts of the body grow slower in relation
to other bones, or even when procceses on the same bone grow at a faster
rate than the rest of the bone.  There is absolutely no evidence that
early birds weren't endotherms.



> As for growth rates, it has been proven that all
> an ectotherm needs is a sufficient supply of food
> in order to equal an endotherm.
> That's why a green iguana has an average growth in
> the wild of 3 years to sexual maturity> 
> Komodo dragons in captivity (and given plenty of 
> food) reach 100 lbs in their first year

     First of all, ectotherms additionally need to have their temperatures
regulated to grow at endothermic rates (which is why 'gator farms spend so
much money on keeping them warm).  Of course, it was hoter in the
Mesozoic.  great, so all the baby dinosaurs needed was a man in a lab coat
to keep bringing them food.  You see, the reason that even tropical
ectotherms don't grow at endothermic rates in the wild is because it costs
calories to go get food.  An ectotherm that has it's body core heated to a
prime level can indeed grow fastwhen food is being delivered to it.  But
it's a much different story when that ectotherm has to get up and go find
its own food.  Not only does it has to waste lots of energy to find enough
food to feed an endothermic growth rate, but all of the different
environments the animal encounters will create thermoregulatory problems
that will move its core temperature away from the ideal (enzyme efficiency
is very strongly related to temperature), forcing it to grow slower, or to
behaviorally change its temperature (ergo it stops looking for food, eats
less, and must grow slower anyway).
     Of course, Hadrosaurs may have fed their young, but no body thinks
they did it for six years (could you imagine a decade old sauropod in a
nest, still waiting for food from its parents?).  Fast growing dinosaurs
were doing something that no living exotherms does in the wild.  This is a
point that even Terry Jones has agreed with me on, although exactly what
the data signifies is still a point of some contention.



> Oh and estimates for _Architeuthis dux_, the giant squid are basing this
> creature as reaching a size of 30ft in only 6 months. 

Fascinating.  Where did you here that?  Of course, aquatic animals are,
for the most part irrelevant to calculating the metabolics of terrestrial
critters/ Locomotion is five to ten times cheaper in the water!


> It just all depends on food access.


     Precisely.


Scott Hartman