[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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




> 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

__________________________________________________
Do You Yahoo!?
Sie sind Spam leid? Yahoo! Mail verfügt über einen herausragenden Schutz gegen 
Massenmails. 
http://mail.yahoo.com