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Re: Tawa hallae: everything you know about basal saurischians is wrong...



I suppose they reconstructed Tawa as hairy because of two things:

1-presence of hair-like integument in ornithischians, pterosaurs, and
coelurosaurs.
2-Recent evidence of high locomotion costs (measured in O2) suggesting
endothermy for at least large bipedal dinosaurs, including
Plateosaurus and theropods. As in the study Tawa resulted as a basal
theropod, this in turn leads to hypothesizing it may have been
endothermic.

2009/12/12 evelyn sobielski <koreke77@yahoo.de>:
>
>
>> http://www.guardian.co.uk/science/2009/dec/10/tawa-hallae-feathered-theropod-mexico
>
> Is there any evidence for this claim?
>
> (And has anybody ever checked GenBank whether the "feather" genes have some 
> sort of viral signature? A "domesticated" papillomavirus or similar would 
> explain the structurally different but physiologically somehow related - as 
> integumental hyperplasies triggered by a fairly simple genetic mechanism, 
> essentially - structures phylogenetically widespread among archosaurs. But 
> its genetic "footprint" would be obvious, and thus this assumption could be 
> tested.)
>
> Nonwithstanding, I find the notion of sticking feathers everywhere a bit 
> dubious; eventually it's likely to result in major embarrassment and a lot of 
> cheering from BANDits. Feathers/fuzz and large-bodied animals living in a 
> tropical climate and well on their way to homothermy do not at all mix well. 
> Phylogenetic bracketing is also unhelpful with such a limited sample of hard 
> evidence; _Elephas_ and _Heterocephalus_ for example would provide a nice 
> bracket that "proves" all mammals, big and small, are almost nude, if we did 
> not know as many mammals as we do.
>
> Absence of quill knobs (and possibly rectrical knobs, which are as of yet 
> unknown but might conceivably have evolved as alternative to a pygostyle) in 
> a large-bodied non-polar non-flying archosaur, I'd presume, is strongly 
> indicative that the critter had no integumentary fuzz, feathers or bristles 
> to significant extent.
>
> One thing that has not been considered: parasites. In general, the 
> maintenance effort of plumage is not especially light; birds spend much of 
> their leisure time (which can be considerable; I once had a project  where I 
> had to observe _Ducula pinon_ as they lazed away 90% of their day time) with 
> preening. Those that feed on carrion more than opportunistically generally 
> have naked heads and possibly necks. So, a soiled plumage seems to be more 
> trouble than it's worth.
>
> Lacking a beak but possessing hands, nonavian theropods would likely soil 
> themselves while feeding more than avian ones do today. And as far as anyone 
> can tell, they did not have an uropygial gland, so bathing would be 
> cumbersome or downright hazardous (wet plumage is a problem except for those 
> birds that are specifically adapted to it. But it seems in the first place a 
> problem, not a benefit; otherwise it is hard to see why loss of waterproofing 
> did not evolve more often than it did).
>
> I see no problem at all with "flight feathers" evolving prior to flight 
> (powered or not); in fact, there are pretty good reasons for them to do 
> (signalling, agility). Downy young - no true down having been found in a 
> nonavian context nonwithstanding - also seem good. But large theropods being 
> fully feathered even as adults? Everything we know about large quadruped 
> physiology says "not a good null hypothesis".
>
>
> Regards,
>
> Eike
>
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