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Re: Fortunguavis, new enantiornithine bird from Lower Cretaceous of China



This is certainly a very interesting new bird.  _Fortunguavis_ is very
stocky for its size (about the size of a pigeon apparently).  But I'm
highly skeptical that it was scansorial, despite the arguments put
forward in the paper.  _Fortunguavis_ looks raptorial to me, and the
arguments put forward by Wang &c in favor of scansorial behavior and
against raptorial behavior aren't especially convincing.

Firstly, there is the claw curvature data.  This is 'iffy' at best.
It is arguably not helpful to their case that Wang &c are so reliant
on the method of Feduccia (1993), which was criticiqued by Fowler et
al. (2011 Supporting Information Text S1.  Hint: Feduccia's study was
crap.).  Fowler &c's study also highlighted the difficulties
associated with delineating claw curvatures associated with
trunk-climbing and predatory lifestyles. The highly recurved pedal
unguals of _Fortunguavis_ are entirely consistent with raptorial
habits.  This also fits with the very stocky pedal phalanges, and the
robust skeleton in general.

Secondly, when Wang &c enter _Fortunguavis_ into the dataset of
Dececchi and Larsson (2011), it comes out in the morphospace occupied
by aerial foragers and birds of prey, not among the climbing birds.
Wang &c state that "only four modern climbers were sampled by Dececchi
and Larsson (2011)"; but in defense of Dececchi and Larsson, these
four birds are fairly representative of modern climbing birds (they
include a treecreeper, a nuthatch, and two woodpeckers).  Not bad,
considering that trunk-climbing is not that prevalent among modern
bird groups.  Trunk-climbing is a fairly specialized behavior among
today's birds, and is used when vertically foraging for food (such as
within the trunk or under bark).  Modern arboreal birds typically just
fly up into trees, and so don't need to climb.  (Okay there is the
juvenile hoatzin, but it's a special case...)

Thirdly, Wang &c argue against predatory habits for _Fortunguavis_
based on a comparison to the phalangeal proportions in certain extant
birds of prey, stating: "In Accipitridae, Falconidae, and Strigidae,
the proximal phalanx of digit II is abbreviated to less than half the
length of the second phalanx (Mayr, 2006; M.W., pers. observ.),
allowing the claw to flex plantarly when catching prey. This phalanx
is long in Fortunguavis."  Yet, this phalanx is long in many non-avian
theropods, including dromaeosaurids.  Also, not all modern birds of
prey have the proximal phalanx of pedal digit II abbreviated.  This is
actually made clear in the paper cited by Wang &c (Mayr, 2006 - the
description of _Masillaraptor_).  For example, it is not the case in
Sagittariidae (secretary bird), Cathartidae (NW vultures), and
Tytonidae (barn-owls); in all these groups the first phalanx of the
second toe is *not* shortened (Mayr, 2006). The highly refined plantar
flexion of the second claw in accipitrids etc probably relates to the
kinds of prey targeted, not to predation per se.

Fourthly, in _Fortunguavis_ the second pedal ungual is larger than the
other anterior toes. This is also characteristic of predatory birds
(again as mentioned by Mayr, 2006).  It is also true for
dromaeosaurids, troodontids, etc (Fowler et al., 2011).

Considering _Fortunguavis_ looks to have been a fairly "advanced"
flier, I don't see why it needed to climb trees in the first place; it
could just fly up to its perch.  Unless, of course, _Fortunguavis_ had
a woodpecker- or treecreeper-like ecology - and there is no suggestion
of that from the skeleton, including the skull.  The retention of
recurved claws on the manus doesn't mean anything, because lots of
Mesozoic birds had proper wing-claws.  A raptorial lifestyle fits with
robust proportions of _Fortunguavis_, especially if it pinned down
struggling prey with its feet.





Cheers

Tim

On Wed, May 7, 2014 at 7:42 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> From: Ben Creisler
> bcreisler@gmail.com
>
> A new bird in the new Journal of Vertebrate Paleontology:
>
>
> Min Wang, Jingmai K. O’Connor & Zhonghe Zhou (2014)
> A new robust enantiornithine bird from the Lower Cretaceous of China
> with scansorial adaptations.
> Journal of Vertebrate Paleontology 34(3): 657-671
> DOI:10.1080/02724634.2013.812101
> http://www.tandfonline.com/doi/full/10.1080/02724634.2013.812101#.U2lW6PldXeI
>
>
> We describe a new enantiornithine bird, Fortunguavis xiaotaizicus,
> gen. et sp. nov, from the Lower Cretaceous lacustrine deposits of the
> Jiufotang Formation in northeastern China. The new taxon has a
> strongly dorsoventrally bowed furcula indicating that enantiornithines
> evolved furcular morphologies in parallel with ornithuromorphs. The
> new specimen has very robust limbs compared with other
> enantiornithines and has an unique foot morphology with metatarsal II
> much shorter than metatarsal IV, robust pedal digits, and strongly
> recurved pedal unguals. Although recurved unguals characterize
> Enantiornithes, the extreme curvature present in Fortunguavis suggests
> scansorial specialization in this species. These features hint at a
> unique ecology for this taxon and further increase the known diversity
> of body plans in Early Cretaceous enantiornithines.