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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
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
2009/12/12 evelyn sobielski <firstname.lastname@example.org>:
> 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
> 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".
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