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RE: Most dinosaurs were scaly

Is it just me, or does this study seem to suffer from naively assuming body 
covering doesn't covary with other factors we can test?  In other words, it's 
obvious if you just plug in known skin coverings over a cladogram, scales will 
be the ancestral state for Dinosauria.  No one's ever doubted that, Greg Paul 
included.  The additional factor which has been discussed ever since his 1988 
work is of course size.  What happens if you only plot small specimens on the 
cladogram?  Ornithischians are all fuzzy/spiny, and sauropodomorphs are unknown 
unless the titanosaur embryos count.  Even if the latter do count, Sciurumimus 
makes theropods primitively fuzzy despite Juravenator, so that's ambiguous 
basal Saurischia and fuzzy basal Dinosauria, which only gets more support if 
pterosaurs are avemetatarsalians.  Maybe Barrett and Evans include a caveat 
about this assumption, but since taking it into account nullifies their entire 
conclusion, I don't think it could help.  This isn't even getting into the 
metabolic and growth evidence that 
shows increasingly basal archosauromorphs weren't like living 
'reptiles'.  You might as well determine ornithischians don't have cheeks based 
only on their lack in birds, crocs and lepidosaurs.

Mickey Mortimer

> Date: Fri, 27 Dec 2013 10:13:58 -0800
> From: bcreisler@gmail.com
> To: dinosaur@usc.edu
> Subject: Most dinosaurs were scaly
> From: Ben Creisler
> bcreisler@gmail.com
> A news item and the original abstract from the 2013 SVP meeting:
> Nature news:
> http://www.nature.com/news/feathers-were-the-exception-rather-than-the-rule-for-dinosaurs-1.14379
> The abstract from the SVP Meeting:
> Poster Session III (Friday, November 1, 2013, 4:15 - 6:15 PM)
> BARRETT, Paul, The Natural History Museum, London, United Kingdom; EVANS,
> David, Univ of Toronto at Mississauga, Toronto, ON, Canada
> Osteoderms and scaly skin impressions are historically well known in non-avian
> dinosaurs
> these structures,
> many dinosaur taxa possessed other integumentary features, including a
> range of ‘quills,'
> filaments, and feathers in non-avian theropods and ornithischians.
> Feathers and their
> homologs are commonly regarded as a synapomorphy of either coelurosaurian or
> tetanuran theropods, but some authors have gone further, using the presence of
> ornithischian feather-like structures to suggest that these structures
> are plesiomorphic for
> Dinosauria. This inference has wide-ranging implications for dinosaur
> biology and
> evolution.
> However, to date, no studies have attempted to assess rigorously the
> evolution of
> dinosaur integumentary structures within a broad phylogenetic context.
> We compiled a
> complete database of all epidermal integumentary structures reported
> in dinosaurs, by
> major body region, in order to investigate the origin of feather
> homologs and the
> evolution of integumentary structures in the clade. Scales are
> definitively present in
> virtually all major ornithischian clades. This, and the presence of
> extensive armour in
> thyreophorans suggests that genasaurian skins were primitively scaly. 
> Similarly,
> sauropodomorphs lack evidence for anything other than scales or
> osteoderms. Fitch
> optimization of integument types on dinosaur phylogenies shows that there is 
> no
> unequivocal support for inferring a deep origin of feather-like
> structures, a result
> supported by maximum likelihood ancestral state reconstructions for
> these characters.
> The structures in Tianyulong and Psittacosaurus are best regarded as
> autapomorphic
> integumentary modifications, and there is currently no strong evidence
> that these features
> are feather homologs. Further work on the chemical composition of
> these structures, and
> those in several non-coelurosaurian theropods, is needed. Although
> ornithodirans exhibit
> a range of integumentary novelties that may be related to the origin
> of feathers, theropods
> are currently the only dinosaurs that display unequivocal e
> feathers and their
> direct homologs.