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Re: feathers and WWD

...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; 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 

(It is not possible to reconstruct the consequences of *any* major niche, 
metabolic or size shift correctly based on phylogenetic bracketing. Elephants, 
rhinos, pinnipeds, cetaceans - none of these could be reconstructed correctly 
based on data from their relatives.)

Still, it is quite safe to assume that _Tyrannosaurus_ hatchlings were fully 

And in any case, some physiologist should do the maths. We have enough 
paleoclimatological data and anatomical data that one could take a range of 
reasonable estimates of basic metabolic/heat exchange rates and calculate how 
much of the animal could be covered in how thick an integumentary insulation 
before it fatally overheats.

But even so, I think it's problematic to imagine an outright plumage on 
nonavian theropods. "Fuzz" or ratite-like plumage, no problem with that at 
least in the small and midsized taxa. Avian-type plumage is maintenance 
intense; I am not sure if preen glands would leave any fossil trace except 
under the most favorable conditions (eg 
http://link.springer.com/article/10.1007/BF02990211) but these as well as a 
beak (ie a sharply pointed snout with keratinous covering) are probably 
mandatory for maintenance of an avian-type plumage.

(What did the avian uropygial gland evolve from? There seems to be very little 
published on this topic.)

It may also be relevant that there are no dinosaurian feather parasites known 
yet. If ALL theropods (and a lot of other dinos) had full plumage at all ages, 
the nonavians can be expected to have been crawling with parasites, since their 
ability to maintain plumage was lower than in avians and even avians are often 
badly affected (Franklin's comment on the Bald Eagle comes to mind). But then 
again, avian lice fossilize even worse than preen glands: 
Molecular phylogenetics of avian lice might be useful. Though the dating would 
be based on DNA alone and hence be rather spurious, the evidence from crown 
Aves indicates host shifts are common (within multispecies breeding colonies as 
in the Mirandornithes vs Anseriformes, between predators and prey such as in 
accipitrids and pigeons). Given that molecular-clock age estimates tend to 
inflate the presumed age of divergence, and in small r strategists strongly so, 
if molecular clocks place the phthirapteran radiation post-mid-Mesozoic, this 
would strongly indicate that at least *these* integumentary parasites only 
arose when avians did. Any difference between Amblycera and Ischnocera early 
radiation patterns may be interesting, because the latter have a much stronger 
host association than the former. 
A relevant paper (though not incorporating the recent years' insights) is 
http://phthiraptera.info/Publications/41865.pdf - suffice to say that lice 
almost certainly evolved from Psocoptera-like ancestors inhabiting and feeding 
on plant debris used as bedding or nesting material by amniotes. There is no 
direct evidence of use of such materials by nonavian dinos, but considering 
_Mei long_ it is not unreasonable to assume at least the smaller taxa used some 
bedding to line their favorite sleeping sites. In that regard, it is again 
interesting to note that large sparsely-haired mammals prefer to rest on soft 
sediment (eg sand or ash http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3466804/) 
rather than gathering bedding material. But whether this is size-related (too 
time-consuming to gather the material) and thus comparable to large dinos, or 
integument-related (no need to keep the integument from soiling) and thus not 
comparable to large dinos in the scope of
 this question, or both, or neither, I don't know. But it's not very relevant, 
because even if  large carnivorous theropods used no bedding themselves, if 
smaller dinos did (possible and perhaps likely) and were preyed upon by the 
large guys (certain), host switching would still be expected *if and only if* 
the large guys had in fact sufficient plumage.
There are three interesting recent papers pertaining to the question, one by 
Grimaldi and Engel (ie entomo guru stuff) 
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1560062/, a recent review of the 
underlying question 
and a 2011 analysis of the molecular data 
which tentatively points to lice only arising coincident with avians (but see 
also http://www.biomedcentral.com/1471-2148/10/292/ for the problems of the 
molecular approach - for Anoplura it does not work as well as one would like it 

All things considered I find the hypothesis of full plumage (or similar 
integument) borne by small theropods very convincing, by large and gigantic 
dinosaurs quite weak and possibly even fully untenable. 

Display feathers are a possibility even in the largest taxa, but even the 
presence of quill knobs is not a very strong argument - these only prove 
bird-like remiges somewhere in the ancestry (if remiges are lost, the quill 
knobs might persist until the now-useless phene gets eliminated by a chance 
mutation; quill knobs and remiges are functionally not firmly related and not 
linked genetically; we know this from the non-universal development of quill 
knobs in volant crown Aves* but the evo-devo link is still unclear - they might 
depend on the physical presence of actual feathers to form properly). The 
"phylogenetic bracketing" argument is weak if not fully spurious because a) it 
flatly disregards a soft constraint (maintenance effort - not prohibitive, but 
potentially debilitating), b) it flatly disregards a possible hard constraint 
(thermodynamics - prohibitive if it applies because the resultant evolutionary 
fitness is zero) and c) it can be
 demonstrated to be false if the same question is applied to crown lineages.

That being said, it's still an open question until someone does the math - we 
know that there is a thermoregulatory threshold, but this needs to be 
calculated even if this calculation will be accurate only to an order of 
magnitude perhaps. In absence of hard figures, it's only notable that extreme 
gigantism and dense integument are apparently only compatible in subarctic 
climates - and as far as anyone can tell, there was no persistent subarctic 
climate *anywhere* during the Mesozoic.**



* Unfortunately, flightlessness in crown avians tends to quickly reduce the 
ulna to an extent that any persistent quill knobs are obliterated. But perhaps 
_Branta hylobadistes_ has some data to offer in this regard; it's the only 
avian taxon I can think off the top of my head that is known from a population 
containing the whole spectrum from weakly volant to fully flightless 
individuals, and the hypodigm is very good - according to the original 
description (Olson & James 1991) there should be dozens, possibly >50 ulnae at 
USNM and/or BPBM representing all the anatomical diversity found in the 
population. _Branta_ quill knobs are not excessively prominent even in 
long-range migratory species however.

** Of course the Mesozoic had the same glacial/interglacial cycle we have 
today, ie there were colder and warmer periods within a generally hot climate. 
It is interesting to speculate if nonavian theropod integument *within* any 
lineage became denser or more extensive during Cretaceous glacials. In mammals 
it apparently did, and mammals are a very good proxy for nonavian dinos as 
regards their ability to shift range in reaction to climate change. (At least 
in the late Mesozoic, after an ecological/ecotrophological equilibrium had been 
established. It's different if a newly evolved and competitively successful 
lineage/radiation is forced to shift range; this will likely be successful to 
the detriment of less sophisticated competitors.)

Thomas R. Holtz, Jr. <tholtz@umd.edu> schrieb am Di, 12.11.2013:

 Betreff: Re: feathers and WWD
 An: hammeris1@att.net
 CC: dinosaur@usc.edu
 Datum: Dienstag, 12. November, 2013 03:45 Uhr
 Don't forget: Walking with Dinosaurs
 came out in 1999, and was being
 animated in 1998. So at that time the degree of feathering
 coelurosaurs was unknown.
 At present, every single dromaeosaurid for which integument
 is known is
 fully feathered, as are the outgroups Troodontidae,
 Oviraptorosauria, and Therizinosauria. (And we have feathers
 on other,
 more distant outgroups).