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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)
DINOSAUR INTEGUMENT: WHAT DO WE REALLY KNOW?
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. Recent discoveries have demonstrated that in addition to
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 evidence of
feathers and their
direct homologs.