Re: feathers and WWD

[Ruben Safir <ruben@mrbrklyn.com>]

On 11/12/2013 06:37 PM, evelyn sobielski wrote:
> 
> --------------------------------------------
> Ruben Safir <ruben@mrbrklyn.com> schrieb am Di, 12.11.2013:
> 
>  Betreff: Re: feathers and WWD
>  An: "evelyn sobielski" <koreke77@yahoo.de>
>  CC: dinosaur@usc.edu
>  Datum: Dienstag, 12. November, 2013 20:40 Uhr
>  
>  On Tue, Nov 12, 2013 at 04:29:21PM
>  +0000, evelyn sobielski wrote:
>  > ...but the case of Mammalia shows that the default
>  position is untenable, especially if the 
>  > metabolic rate of theropods was as high as their
>  anatomy indicates. Whether anything heavier 
>  > than a horse could maintain a thermal insulation by a
>  dense coat of integumentary structures 
>  > (feathers in this case) in the Mesozoic climate (with
>  subtropical conditions almost up to the 
>  > polar circles) is very questionable; 
>  
>  > Ostriches don't live in amazingly hot conditions?
> 
> Totally do, they are close to outright desert birds. But an adult male 
> ostrich weighs shy of 150 kg (twice the weight of _Deinonychus_), and even so 
> they have extremely slender and little-insulated necks and legs (appreciably 
> different at the cervical vertebra level) for shedding excess heat. They are 
> no tyrannosaurids but close enough to be interesting.
> 
> As I said: I would like to see the math. Ostriches are avian metabolism 
> models of some significance, the raw data are there. Since ostriches are 
> tropical, you don't even need to correct for warmer climate. Just plug in a 
> range of reasonable estimates of mass, surface area, and metabolic rates for 
> _Tyrannosaurus_ (or whatever theropod you like) into the equations, and see 
> how much excess heat the theropod had to shed to avoid overheating. Then do 
> the math assuming no integument. Then assuming the theropod was fully covered 
> in Tetraonidae- or Mergini-type plumage (these are among the most insulating 
> we get, and also conveniently plesiomorphic by avian plumage standards).
> 
> It should be possible if you are a physiologist and know what equations and 
> variables you need, but nobody seems to have done it yet and I am no 
> physiologist. But TBH it's only 10 years or so that we actually have the 
> results from the computer models that allow reliable estimates of dinosaur 
> surface area and (to a lesseer extent) mass 
> http://www.youtube.com/watch?v=5RG0yLeJE_U. Any earlier calculations would 
> have ben not very informative.
> 

There are two other factors to consider, FWIW.  first, Oxygen levels
were very different.  Secondly, COLOR.  It matters.  The insulation
works two ways.  I white sheet of feathers might well prevent over
heating of a highly active creature.

This is just amateur idle speculation on my part ... but..


>  
>  > phylogenetic reasoning is usually a good approach, but
>  in this case the constraint is basic 
>  >physics, and physics always wins over phylogeny: it's
>  hard to maintain your lineage if you are 
>  >dead form heatstroke.
>  
>> So, if I understand you correctly, you're saying that a trex
>  with
>  feathers is unlikely because the climate was too hot?
> 
> No, I think it's unlikely because from what we know in birds and mammals, and 
> from what basic physics tells us, maintaining evolutionary fitness (ability 
> to survive as a species = gene pool) in the face of heatstroke would have 
> been a major issue of concern for any megafauna that walk around all year 
> thickly insulated under average temperatures of 20+°C and are at least well 
> advanced towards autothermy.
> 
> Conservation of energy. Like with spaceships: Accelerating is not the 
> problem, if you have time (They had a few million years). Slowing down is. 
> the problem.
>

I'm not sure I can understand how you split the difference on this and
what I said.  If i understand, the bottom line is that it is not likely
them to be feathered within that climate?


> Climate is a factor insofar as the ambient temperature (in space flight, your 
> starting speed) is higher, and if you are *only* "well advanced towards 
> autothermy" it may be a major factor. It's relevant evolutionarily insofar 
> that it did not make the challenge of shedding excess heat any *easier* and 
> that's for shure, you can't cheat thermodynamics. If there were a physical 
> limit in body size/metabolism/integument combinations today, there was a 
> *higher* limit in the Mesozoic.
> But the ostrich data should be good enough to allow disregarding climate at 
> first.
> 
> One aspect of the warmer climate argues in favor of much plumage even on 
> large theropods tho: it makes an excellent raincoat, and you don't even need 
> an uropygial gland do keep it in shape. Tropical rainforest mammals tend to 
> have sleeker, smoother and shorter fur than subtropical relatives, but 
> rainforest flightless birds (as far as we know; there weren't so many) 
> were/are all notably shaggy. And the main consequence of a warm climate is an 
> accelerated water cycle, ie a global increase in precipitation (more water in 
> the atmosphere and it gets turned over more quickly). So even though there 
> were vast Cretaceous deserts, a widely successful radiation of large land 
> animals at that time would more often than not have to cope with strong 
> downpours on a regular basis. 
> But if plumage is lethally dense if dry, or if waterlogged, makes no 
> difference. Dead is dead.
> 
> 
>  
>> So elephants and Hippos are virtually hairless?
> 
> Not hairless, *fur*less. Not featherless, *plumage*less. (Mammalian skin is 
> rarely hairless, but plumage grows in tracts, the areas between being 
> entirely nude; it's an interesting but probably minor factor in the whole 
> issue)
> 
> Hippos are aquatic, theropods weren't (until _Gansus_ or so, and perhaps with 
> a few specialist exceptions other than that). Technically it would not be 
> unsurprising if one found hippos thickly furred (considering the niche), but 
> evolution usually discovers blubber first, as it did in their case. Hippos 
> are a poor analogue except for... other hippos I guess. And a bunch of 
> Paleogene mammals of more or less disputed affiliation.
> 
> 
> Any case, It's not just one line of evidence. The maintenance needs of 
> plumage are another, the lack of actual fossil *proof* another etc. 
> Altogether I find the reasons to assume full plumage should not be lost and 
> re-evolved in a size-constrained fashion within a short time and multiple 
> times (in fact any time a size increase above some threshold happened) to be 
> very weak. The density of mammalian fur is so plastic phylogenetically, and 
> avian pterylosis is also very much noninformative as regards phylogeny if you 
> go back beyond the Neogene (arranging avian "orders" by pterylosis is 
> hopeless), and the genetics are obviously plastic too (think show fowl 
> breeds, alopecia and hirsutism phenotypes). The Mesozoic hypodigm of isolated 
> fossil feathers is not indicative of any large-bodied animals and in general 
> (especially as regards pennaceous feathers) closely follows the radiation of 
> avians and parallel small volant theropod lineages. And so on.
> 
> That being said, for any theropod of dog or smaller size I would assume that 
> a comprehensive "plumage" is the null hypothesis. Maybe not with feathers 
> like those we usually think of first, but then again, the stuff cassowaries 
> grow from their skin doesn't look very much like such feathers either. Very 
> early in theropod evolution there seems to have emerged something only a 
> little less complex, and visually probably not that much different.
> 
> 
> Regards,
> 
> Eike
> 
> 
>