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AW: Evolution of dinosaur epidermal structures (free pdf)
I recently came across this study which might be relevant to the question of
Aiello & Wheeler (2003): Neanderthal thermoregulation and the glacial climate.
In: van Andel & Davies (eds): Neanderthals and Modern Humans in the European
Landscape during the Last Glaciation: Archaeological Results of the Stage 3
Presently, we have very little actual data on the larger dinos, because there
are too few sufficiently complete fossils (and that's not likely to change).
What Aiello & Wheeler did was to calculate, from morphological data and robust
assumptions on physiology/thermoregulation, up to what ambient temperature
Neanderthal and Modern humans could survive without clothing. They found the
difference to be slight enough to necessitate some form of light clothing or an
exceptionally hairy (by human standards) integument for Neanderthals to survive
in a glacial climate.
This approach could probably be used the other way around, to determine whether
fully feathered dinosaurian megafauna could survive without special adaptations
to get rid of excess body heat. With actual evidence (say, a fairly complete
sauropod or tyrannosaurid mummy) not likely to be forthcoming in any quantity
(or at all), robust inference would be the best approach to tell whether
dinosaurian megafauna would have been (secondarily, in the case of many or all
theropods) unfeathered as adults - or more precisely, down to what latitude
dinosaurian megafauna could survive all year round if fully feathered and
lacking special heat-shedding adaptations. Possibly, it would even allow us to
make a pretty robust statement on migratory behavior of polar dinos - if their
metabolism was effective enough to allow fatal overheating during polar summer
if feathered, it suggests they a) weren't feathered and b) had to migrate
during polar winter.
What's nice about the Aiello/Wheeler approach is that it needs no data other
than what we have (or can reasonably assume) for dinos - just what information
on body layout, musculature etc you can infer from the fossils, and some robust
assumptions about metabolism/physiology. The latter is a bit more tricky in
dinos, but it should by now be possible. The ambient temperature at various
latitudes during various parts of the Mesozoic is also researched well enough
to be usable. (In particular, the Triassic is crucial - the basal dinosaurs
lived under strong hothouse conditions, possibly the hottest/driest climate
ever experienced by amniotes)
We wouldn't get a definitive value for any particular lineage, but rather
cut-off conditions which no lineage could physiologically exceed; with these we
could see if a particular taxon did exceed these at a particular latitude, or
not. Birds could be used to test the reliability of the approach - if pluggin
in sandgrouse data (of which there is quite a lot) yields the result that they
can't avoid fatal hyperthermy *only* at the most extreme temperatures found on
today's Earth surface, we know the maths are sufficiently reliable.
It would certainly more robust than phylogenetic bracketing, which requires a
good taxonomic sample to work - but the dinosaurian integument sample is
extremely biased towards small avialans (which we know to be fully feathered),
i.e. the least interesting/critical taxa; we'd need data on medium-sized basal
theropod integument we don't have, resulting in a bracket that is too wide and
too biased to be confident.
Of course, we might find that the heat retention caused by plumage is small
compared to other factors, similar to the original case with Homo. That would
be interesting nonetheless, because it would mean that thermoregulation has
been overestimated as a factor in plumage evolution.
Note that this approach is not very informative regarding *hatchling*
integument - a case could be made for all dino hatchlings to be fully feathered
from the very start of the lineage, or even for hatchling "plumage" (in a loose
sense, ie including pycnofibres) to be plesiomorphic for Avemetatarsalia,
because of metabolic constraints (nonhomothermy) and bracketing (in the absence
of integument from basal avemetatarsalians). And in crown dinos, well-developed
plumage in hatchlings is the ancestral condition even though their
post-hatching ontogeny is accelerated compared to non-ornithuromorph avialans.
Unfortunately, pterosaurian data are not very helpful, because their
surface/volume ratio was exceptionally high throughout, so whatever their
metabolism, any heat-retaining mechanism would give them a fitness advantage
more pronounced than in all other terrestrial vertebrates (except bats, *if*
pterosaurs were as endothermic as bats. Which they probably weren't.).
Ben Creisler <email@example.com> schrieb am Mi, 3.6.2015:
Betreff: Evolution of dinosaur epidermal structures (free pdf)
Datum: Mittwoch, 3. Juni, 2015 17:15 Uhr
A new paper in open access:
Paul M. Barrett, David C. Evans & Nicolás E. Campione
Evolution of dinosaur epidermal structures.
Biology Letters 11: 20150229
Spectacularly preserved non-avian dinosaurs with
filaments/feathers have revolutionized dinosaur studies and
the suggestion that the dinosaur common ancestor possessed
integumentary structures homologous to feathers. This
major implications for interpreting dinosaur biology, but
has not been
tested rigorously. Using a comprehensive database of
traces, we apply maximum-likelihood methods to reconstruct
phylogenetic distribution of epidermal structures and
evolutionary history. Most of these analyses find no
evidence for the appearance of protofeathers in the dinosaur
ancestor and scales are usually recovered as the
but results are sensitive to the outgroup condition in
Rare occurrences of ornithischian filamentous integument
represent independent acquisitions of novel epidermal
are not homologous with theropod feathers.
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