[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



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/