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Re: Archaeopteryx feathers and origin of flight based on 11th specimen

It is definitely an intriguing specimen and a great new paper! However, I would 
argue that too much is being made of weather asymmetry. There is nothing 
magical that happens when a feather is slightly asymmetric. In fact, flightless 
birds often have asymmetric primaries, they just are as asymmetric as in flying 
species (on average). The mechanical implications of feather asymmetry are not 
fully understood, but there is some basic knowledge of the mechanics involved. 
Treating asymmetry as a presence/absence character and as an aerodynamic “black 
box” therefore strikes me as a bit unwarranted at this stage. Discussions of 
things like aeroelastic stability should be starting to enter the conversation 
on a regular basis. 

Incidentally, another possibility to be considered: flight is basal to the 
common ancestor of Archaeopteryx and Microraptor, and Archaeopteryx (among 
other taxa) was secondarily flightless.



On Jul 3, 2014, at 1:42 AM, Tim Williams <tijawi@gmail.com> wrote:

> I like the hypothesis that pennaceous feathers initially evolved for
> display, but were exapted for aerodynamic functions in different
> lineages independently.  But the study is intriguing for many other
> reasons.
> * If it is the case that flight was present in the most recent common
> ancestor of _Archaeopteryx_ and modern birds, then according to the
> phylogeny presented in this study, _Balaur_ and _Epidexipteryx_ were
> secondarily flightless ("neoflightless" to use Greg Paul's parlance,
> though personally I hate the word).  However...
> * It is by no means certain that _Archaeopteryx_ was capable of
> flight.  And by "flight" I mean true flight - powered and sustained.
> Not just fluttering hops or glides.  Nevertheless, the wing feathers
> (remiges) certainly appear to be aerodynamic, and suggest aerial
> abilities of some kind.  If so, aerial abilities were acquired
> independently by _Microraptor_ (which even developed an alula).  On
> the issue of the remiges, Foth et al. state:
>    "Elongated, symmetrically shaped pennaceous remiges first appear
> in the stem species
>     of Pennaraptora, whereas asymmetrical aerodynamically shaped
> remiges were convergently
>     developed in the dromaeosaurid _Microraptor_ and the common
> ancestor of _Archaeopteryx_
>     and Pygostylia."
> Foth &c do not directly address the question of whether or not
> _Archaeopteryx_ could actually fly.  That's fine, because flight is as
> much to do with the skeleton and the musculature as the feathers, and
> this study was principally concerned with _Archaeopteryx_'s plumage.
> Besides, we may never actually be confident in gauging
> _Archaeopteryx_'s flight abilities, since although its wings appear to
> have been much like those of a modern flying bird, its entire skeleton
> was substantively different.  There's not even agreement over whether
> _Archaeopteryx_ could raise its humerus above its back, which is
> essential for a complete wing stroke.
> * I think it is entirely possible that the origin of avian flight was
> *both* "ground-up" and "trees-down" - and that "ground-up" preceded
> "trees-down" in a long (and possibly complicated) process by which
> birds evolved flight.  Basal terrestrial avialans might have engaged
> in aerodynamic behaviors that included brief flapping leaps and/or
> glides - rather than true flight.  After all, these behaviors are used
> by certain terrestrial birds in the modern world that are either
> flightless (kagu) or nearly so (lyrebirds, scrub-birds).  Later, after
> avialans became more arboreal, true flight evolved - maybe in basal
> ornithothoraceans, though possibly earlier (such as at the level of
> confuciusornithids or sapeornithids, both of which show likely
> perching adaptations - especially sapeornithids).  Anyway, this is
> just one possible interpretation of the ecomorphology of Mesozoic
> avialans, but I think it accords with the available evidence.
> On Thu, Jul 3, 2014 at 3:53 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>> Ben Creisler
>> bcreisler@gmail.com
>> A new paper in Nature magazine:
>> Christian Foth,  Helmut Tischlinger & Oliver W. M. Rauhut (2014)
>> New specimen of Archaeopteryx provides insights into the evolution of
>> pennaceous feathers.
>> Nature 511: 79–82 (03 July 2014)
>> doi:10.1038/nature13467
>> http://www.nature.com/nature/journal/v511/n7507/full/nature13467.html
>> Discoveries of bird-like theropod dinosaurs and basal avialans in
>> recent decades have helped to put the iconic 'Urvogel' Archaeopteryx
>> into context and have yielded important new data on the origin and
>> early evolution of feathers. However, the biological context under
>> which pennaceous feathers evolved is still debated. Here we describe a
>> new specimen of Archaeopteryx with extensive feather preservation, not
>> only on the wings and tail, but also on the body and legs. The new
>> specimen shows that the entire body was covered in pennaceous
>> feathers, and that the hindlimbs had long, symmetrical feathers along
>> the tibiotarsus but short feathers on the tarsometatarsus.
>> Furthermore, the wing plumage demonstrates that several recent
>> interpretations are problematic. An analysis of the phylogenetic
>> distribution of pennaceous feathers on the tail, hindlimb and arms of
>> advanced maniraptorans and basal avialans strongly indicates that
>> these structures evolved in a functional context other than flight,
>> most probably in relation to display, as suggested by some previous
>> studies. Pennaceous feathers thus represented an exaptation and were
>> later, in several lineages and following different patterns, recruited
>> for aerodynamic functions. This indicates that the origin of flight in
>> avialans was more complex than previously thought and might have
>> involved several convergent achievements of aerial abilities.
>> News stories:
>> http://news.nationalgeographic.com/news/2014/07/140702-archaeopteryx-fossil-feathers-dinosaurs-science/
>> http://blogs.discovermagazine.com/d-brief/2014/07/02/early-bird-fossil-snapshot-feather-evolution/