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Re: feathers and WWD



It's worth keeping in mind that insulation works both ways. Plumage keeps birds 
warm when it's cold and cool when it's hot. Male turkeys lost the feathers on 
the head and neck apparently for display purposes, and they are prone to heat 
stroke because they /lack/ feathers in these areas, which have no insulation 
against direct sunlight.

Ostriches are very well adapted to desert environments. They have patches of 
naked skin on the flank and underside of the wing, which can act as a vent 
while the feathers on the top of the body and the wing act to shade the naked 
flank and legs from the damaging sun.

Animals like Utahraptor unquestionable evolved from animals feathered literally 
snout to toe. Any naked patches were secondarily naked and probably just bare 
skin, not covered in scales, which offer reptiles protection from the sun. 
Utahraptor or any secondarily large dinosaurs with fluffy ancestors would 
probably /require/ at least some strategic feathering to help regulate their 
temperature and provide shade to avoid sunburn and heat stroke.

Matt

Sent from my iPad

> On Nov 12, 2013, at 6:37 PM, evelyn sobielski <koreke77@yahoo.de> 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.
> 
> 
>> 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.
> 
> 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
> 
>