Re: [dinosaur] Archaeopteryx had active flapping flight ability based on wing bone geometry (free pdf)

[Tim Williams <tijawi@gmail.com>]

> Dennis F. A. E. Voeten, Jorge Cubo, Emmanuel de Margerie, Martin RÃper, 
> Vincent Beyrand, Stanislav BureÅ, Paul Tafforeau & Sophie Sanchez (2018)
> Wing bone geometry reveals active flight in Archaeopteryx
> Nature Communications 9, Article number: 923


Reading between the lines, there's not much love here for the arboreal
('trees-down') origin of flight in birds - at least insofar as
_Archaeopteryx_ is concerned.  A 'flapping-start' origin of flight
appears far more likely than a passive glider.

Voeten &c: "The three specimens of _Archaeopteryx_ were found to
unanimously ally with birds that incidentally employ flapping flight
to evade predators or cross physical barriers, through which we
interpret that _Archaeopteryx_ actively used its wings to take to the
air."
This finding is entirely consistent with a terrestrial origin of
flight - especially if flight abilities evolved in small, cursorial
bipeds that used their forelimbs to help launch themselves over
terrestrial obstacles, or to elude a pursuing predator on the ground.

Voeten &c: "In contrast [to the pterosaurian and chiropteran flight
apparatus], even the oldest avian wings represent specialised anterior
limbs that are inherently mobile and structurally connect to the body
exclusively through articulation with the glenoid. Such a particular
modification of the non-avian maniraptoran arm, which constitutes a
highly dexterous limb in its own right, sharply disagrees with the
conventional condition shared by limbed amniotes primarily adapted to
passive gliding."
So no support for a passive gliding stage on the path to avian flight.
Voeten &c's work is another nail in the coffin for an arboreal glider
ancestry.  (A passively gliding pro-avian is the centerpiece of the
BANDit view of the origin of flight.)

Voeten &c: "The origin of the modern avian flight stroke was
conceivably promoted by selective pressure towards vertical take-off".
This is an idea borrowed from Mayr 2017 (DOI
10.1007/s10336-017-1451-x), which is cited here.  I disagree.  There's
no evidence that the supracoracoideus pulley, keeled sternum,
dorsolateral glenoid fossa, or alula were necessary for a vertical
take-off.  Vertical take-offs are initiated by the hindlimbs in extant
birds (Earls 2000 JEB 203: 725-739), and it's likely that
_Archaeopteryx_ was capable of the same (leaping into the air, with no
need for a running take-off; Dececchi et al. 2016 DOI
10.7717/peerj.2159). The wings are deployed for the climb-out phase of
the launch, and a modern avian flight stroke is not essential for this
- just large wings capable of thrust generation.

The next obvious step is to look at _Microraptor_'s cross-sectional
wing bone geometry.  I'd be surprised if it doesn't also point to
flapping-flight abilities.