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Re: Dinosaur color vision and evolution of feathers



This is the latest of several recent papers that have advocated a
non-aerodynamic function for the evolution of planar, pennaceous
feathers.  According to this hypothesis, the development of pennaceous
feathers was associated with display and ornamentation, and/or balance
and maneuverability during locomotion on the ground.  In short,
pennaceous feathers and "wings" (= pennibrachia) initially evolved in
non-arboreal, non-gliding/non-volant theropods, and were only later
exapted for aerial locomotion.

I think it's worth noting that the great John Ostrom promulgated
similar ideas back in the 1970's.  Ostrom wrestled with an apparent
paradox in _Archaeopteryx_: "essentially modern "flight" feathers in
the absence of virtually all of the skeletal specializations that are
associated with (or required for?) modern bird flight..." (Ostrom,
1974).  Ostrom's solution was unorthodox: that _Archaeopteryx_ used
its "wings" as insect-trapping devices as part of a predatory strategy
by a cursorial theropod to catch flying insects.  Ostrom's hypothesis
never really took off; but the paradox hasn't gone away.  Ostrom at
least recognized a problem that many others before and since have
chosen to ignore or overlook: the skeleton of _Archaeopteryx_ has
absolutely no clear adaptations for either arboreality or powered
flight.  The same problem extends to every other non-avialan or basal
(non-pygostylian) avialan theropod from the Jurassic and Cretaceous,
including _Aurornis_, _Anchiornis_, _Xiaotingia_, _Eosinopteryx_,
_Epidexipteryx_, _Epidendrosaurus_, _Microraptor_, _Pedopenna_,
_Jinfengopteryx_, and _Jeholornis_.  Some folks have discerned
arboreal adaptations in a subset of these pennaraptorans (especially
_Archaeopteryx_, _Epidendrosaurus_, and _Microraptor_ - although not
necessarily sharing the same "arboreal" adaptations).  But in the cold
light of day, none of these characters stack up as being compelling
(or even convincing) evidence for arboreality.  Certain papers
mentioned recently on the DML (e.g., Palmer, 2014 - _Microraptor_'s
plumage conferred no advantage for arboreal gliding; Lefevre et al.
2014 - _Jeholornis_ was cursorial and non-perching) also fit this
narrative.

The debate over the primordial function of pennaceous feathers will
continue - as it should.  But thankfully some old assumptions do seem
to be falling by the wayside, such as the one that states that
asymmetrical feathers always = flight.

On Sat, Oct 25, 2014 at 3:30 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
>
> New papers:
>
> How dinosaur color vision may have led to the evolution of pennaceous
> feathers for display before feathers were adapted for flight:
>
> Marie-Claire Koschowitz, Christian Fischer & Martin Sander (2014)
> Beyond the rainbow.
> Science 346 (6208): 416-418
> DOI: 10.1126/science.1258957
> http://www.sciencemag.org/content/346/6208/416.summary
>
>
> Once believed to be a diagnostic feature of birds, feathers are now
> known to have evolved in dinosaurs well before the first birds. In
> birds, feathers serve several functions: Down feathers insulate the
> body, whereas planar or pennaceous feathers are necessary for flight,
> communication, camouflage, and brooding (see the first figure). What
> was their original function in nonavian dinosaurs? Based on a specimen
> of Archaeopteryx that preserves a spectacular plumage of pennaceous
> feathers, Foth et al. recently hypothesized that pennaceous feathers
> did not evolve for flight but for display. Together with insights into
> body size evolution in dinosaurs along the line to birds and the
> discovery of protofeathers in early dinosaurs, these results
> contribute to an emerging understanding of why pennaceous feathers may
> have been superior to filamentous protofeathers.
>
> **
>
> News and news release (in German)
>
> http://www3.uni-bonn.de/Pressemitteilungen/244-2014
>
> http://www.spiegel.de/wissenschaft/natur/dinosaurier-entwickelten-federn-um-zu-kommunizieren-a-998665.html
>
> =====================
>
> Another recent paper about the structure of feathers:
>
> In Open Accesss
>
> Christian M. Laurent, Colin Palmer, Richard P. Boardman, Gareth Dyke
> and Richard B. Cook (2014)
> Nanomechanical properties of bird feather rachises: exploring
> naturally occurring fibre reinforced laminar composites.
> Journal of the Royal Society Interface 6 vol. 11 no. 101 20140961
> doi: 10.1098/rsif.2014.0961
>
> http://rsif.royalsocietypublishing.org/content/11/101/20140961
>
> Flight feathers have evolved under selective pressures to be
> sufficiently light and strong enough to cope with the stresses of
> flight. The feather shaft (rachis) must resist these stresses and is
> fundamental to this mode of locomotion. Relatively little work has
> been done on rachis morphology, especially from a mechanical
> perspective and never at the nanoscale. Nano-indentation is a
> cornerstone technique in materials testing. Here we use this technique
> to make use of differentially oriented fibres and their resulting
> mechanical anisotropy. The rachis is established as a multi-layered
> fibrous composite material with varying laminar properties in three
> feathers of birds with markedly different flight styles; the Mute Swan
> (Cygnus olor), the Bald Eagle (Haliaeetus leucocephalus) and the
> partridge (Perdix perdix). These birds were chosen not just because
> they are from different clades and have different flight styles, but
> because they have feathers large enough to gain meaningful results
> from nano-indentation. Results from our initial datasets indicate that
> the proportions and orientation of the laminae are not fixed and may
> vary either in order to cope with the stresses of flight particular to
> the bird or with phylogenetic lineage.
>
> News stories:
>
> http://www.nanowerk.com/nanotechnology-news/newsid=37830.php
>
> http://www.futurity.org/feathers-birds-flight-788452/