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Re: Parapengornis eurycaudatus, new enantiornithine bird species from Lower Cretaceous of China



_Parapengornis_ is regarded as a possible arboreal bird, perhaps even
capable of vertical climbing, as in woodpeckers.  However, the authors
make the excellent point that in pengornithids the trochlea of
metatarsal III extends beyond that of the other metatarsals, which
seems at odds with the highly refined arboreal abilities suggested by
the long and reversed hallux.  In modern arboreal perching birds the
three major metatarsals end at around the same level, which is
regarding as an adaptation for perching on branches.  The latter
feature is seen in longipterygids, such as _Longipteyx_ and
_Boluochia_; but not in most enantiornithines in which the pes
otherwise show good grasping abilities, including a long and reversed
hallux (courtesy of the J- or P-shaped metatarsal I). Having
metatarsal III extending beyond the neighboring metatarsals is also
found in mostenantiornithines, as well as more basal
[non-ornithothoracine] avialans and basal ornithuromorphs.  To me,
this is 'weird' - as if most enantiornithines and ornithuromorphs were
not committed to an arboreal lifestyle, and still spent most of their
time on the ground, or in water.  That is, until the neornithines came
along (a point made by the authors in the _Parapengornis_
description).

I'm not wholly convinced of woodpecker-like habits for
_Parapengornis_.  It is true that the ivory-billed woodpecker
(_Campephilus principalis_) has an elongated metatarsal I and hallux -
this particular scansorial bird was studied in detail by Bock and
Miller (1959), a study that is cited several times in the
_Parapengornis_ description.  As Bock and Miller (1959) make clear, in
the ivory-billed woodpecker the metatarsal I and hallux are highly
specialized - the first toe has lost contact with the second toe, and
has swung from a medial to a lateral position, such that it contacts
the fourth toe.  When vertical climbing, the three longest toes can be
directed forward, with the hallux splayed laterally, and the the
plantar surface of the tarsus pressed
against the tree trunk.  This arrangement is ideal for vertical
climbing, where a reversed hallux is not of much use (in most
woodpecker species the hallux is degenerate or absent).  Bock & Miller
refer to this highly specialized scansorial foot of certain
woodpeckers as "ectoropodactyl", which evolved from the zygodactyl
foot.  (Zygodactyly is still used in these birds for perching and
terrestrial locomotion).  There is no suggestion that any
enantiornithine had this kind of highly specialized foot, so the
comparison of a long and reversed first toe between _Parapengornis_
and woodpeckers seems inapt.  A long and reversed hallux is actually
not much use in vertical climbing and clinging - to oppose the force
of gravity, it's better for the first toe to be directed forward or
sideways.






On Thu, Jun 4, 2015 at 4:07 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
>
>
> New in PLoS ONE:
>
>
> Han Hu , Jingmai K. O’Connor & Zhonghe Zhou (2015)
> A New Species of Pengornithidae (Aves: Enantiornithes) from the Lower
> Cretaceous of China Suggests a Specialized Scansorial Habitat
> Previously Unknown in Early Birds.
> PLoS ONE 10(6): e0126791.
> doi:10.1371/journal.pone.0126791
> http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126791
>
> We describe a new enantiornithine bird, Parapengornis eurycaudatus
> gen. et sp. nov. from the Lower Cretaceous Jiufotang Formation of
> Liaoning, China. Although morphologically similar to previously
> described pengornithids Pengornis houi, Pengornis IVPP V18632, and
> Eopengornis martini, morphological differences indicate it represents
> a new taxon of the Pengornithidae. Based on new information from this
> specimen we reassign IVPP V18632 to Parapengornis sp. The well
> preserved pygostyle of the new specimen elucidates the morphology of
> this element for the clade, which is unique in pengornithids among
> Mesozoic birds. Similarities with modern scansores such as woodpeckers
> may indicate a specialized vertical climbing and clinging behavior
> that has not previously been inferred for early birds. The new
> specimen preserves a pair of fully pennaceous rachis-dominated
> feathers like those in the holotype of Eopengornis martini; together
> with the unique morphology of the pygostyle, this discovery lends
> evidence to early hypotheses that rachis-dominated feathers may have
> had a functional significance. This discovery adds to the diversity of
> ecological niches occupied by enantiornithines and if correct reveals
> are remarkable amount of locomotive differentiation among
> Enantiornithes.