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



ottscay@uwyo.edu wrote:
> 

> 

> > =================================

> > 

> > 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.

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

Oh, like lying in the shade is a strictly ectothermic trait.

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

> 

> > 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."

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

This question was brought up on the list before and (I believe) Tom Holtz
explained away why this wasn't a feathered dilophosaur.

If the archives are up again then feel free to check for yourself (The subject
of the thread was Feathered Dilophosaur)

====================================================
> 

> > _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.

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

Yeah, I suppose that's why most ectotherms don't have insulation. Of course
most is not all.

We have leatherback sea turtles and white pointer sharks that have thick
layers of fat for insulation.

Tarantulas and many insects have a fur like covering to conserve heat as well.

Then there's pterosaurs. Which brings me to my next question.

Isn't it strange that in pterosaurs, arthropods and mammals all the insulating
covering is fur, yet in birds it is feathers?

If fur is the evolutionary default, then deinosaurs should have grown fur if
they were endothermic, but they didn't. 

It seems that some evolved a type of feather, perhaps even evolving feathers.
Why is that?

Well if insulation isn't why birds evolved feathers, then what else do we
have. 

There's the aerodynamics of it. Of course the evolutionary default for
ornithoptering is a membranous skin. Not feathers.

Again feathers might have been some strange twist on the same formula. It's
happened before. But there is still something bothersome about that. It just
doesn't seem like that is a plausible reason to evolve feathers.

Fur had already proven itself a fine insulator, so why feathers.

Well what else are feathers good for. Think cockatiel, peacock, umbrella
birds, etc.

All these birds use their feathers for display purposes. Now reptiles have
developed all kinds of freaky display appendages to them. And since feathers
are modified scales, it would seem plausible that the original use of feathers
is for display purposes, not endothermy, nor aerodynamics.

As for why feathers evolved to replace scales, I'm still not sure of. 

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

 

> > 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.

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

Interesting. If you have any citations to go with this I'd love to check into
that. Mainly to see what type of ectotherms were examined. I want to make sure
they are using a good list.

Also you said that many of these papers failed to check for the annuli.
Perhaps a recheck is in order. You know, to be sure.

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

> 

> 

> > 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). 
========================================================
============================================================

Hold on one second. Let's get something straight, ectotherms are not
cold-blooded. The only cold-blooded things I know of today are rocks and
semi-trucks. 

An ectotherm does regulate it's own temperature and does not require it being
regulated for it.

As for alligator farms, I'd like to know what areas of the country (world) you
are talking about. Many (if not all) of the gator farms down south have
outdoor enclosures. 

Not to mention the fact that alligators usually keep their temperatures above
that of their surounding as it is, so the places you are talking about must be
up north somewhere, where they are already out of their natural environment.

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

 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.  
==============================================================
==============================================================

Yeah it does, and many ectotherms (why we don't just say reptiles, since it
seems to be what we are obviously talking about here) do have endothermic
growth rates. Take a look at anoles or fence lizards. They grow to adults in a
couple of months and survive for a substantial amount of years.

I already gave one example of a large reptile with an endothermic growth rate
in the wild. The green iguana, which grows to sexual maturity in a mere 3
years and then goes on to live perhaps a good 25 years. 

That's almost the same growth rate as your average housecat (which does not
reach full growth until around 2 years anyway)

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

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).
=========================================================
============================================================

Yeah, you'd think so, but since many large reptiles have body temperatures
anywhere from 10-60 degrees warmer than there environments, the reduction in
temperature isn't as severe as once thought.

And then there is the really strange _Palmatogecko rangei_ of the Namib
desert. Small little geckos that are only active when the desert temperature
reaches 45 degrees Farenheight. 

You've just gotta love those exceptions to the rules :)

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


>      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.

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

Did you mean ectotherm or endotherm in that last post? Oh Well, either way is
likely to be true.

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

> 

> 

> > 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!

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

True, too bad it doesn't make finding food that much easier. Especially if you
grow up at the bottom of the ocean.

Must be all those thermal vents I guess.

As for a citation on that one, it was National Geographic's: Search for
Architeuthis. 

Too bad they didnt' find it, good shots of sperm whales though. 

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

> > It just all depends on food access.

> 

> 

>      Precisely.

> 

> 

> Scott Hartman

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

Well at least we're in agreement with one of these statements :)

Archosaur J


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