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Gobipipus, new enantiornithine from Mongolia and other new Mesozoic bird papers

From: Ben Creisler

A number of new Mesozoic bird papers:

E. N. Kurochkin, S. Chatterjee & K. E. Mikhailov (2013)
An embryonic enantiornithine bird and associated eggs from the
Cretaceous of Mongolia.
Paleontological Journal 47(11): 1252-1269
DOI: 10.1134/S0031030113110087

Enantiornithes is the most speciose clade of Cretaceous birds, but
many taxa are known from isolated postcranial skeletons. Two embryonic
enantiornithine bird skeletons of Gobipipus reshetovi gen. et sp. nov.
from the Upper Cretaceous (Campanian) Barun Goyot Formation of the
Gobi Desert in Mongolia provide new insights into the anatomy,
radiation, and mode of development of early avialans. In recent times,
both enantiornithine and ornithuromorph birds are known from the Barun
Goyot Formation as well as from the Djadokhta and Nemegt Formations.
The 80-million-year-old Gobipipus skeletons encased within eggshells
shows several features characteristic of enantiornithine birds. The
wing skeleton and shoulder girdle show morphological features
indicating that Gobipipus achieved sophisticated powered flight.
Gobipipus reshetovi gen. et sp. nov. is quite distinct from the
sympatric enantiornithine species Gobipteryx minuta from the same
strata in many anatomical features. Phylogenetic analysis of 26
avialan ingroup taxa based on distribution of 202 characters indicate
that Gobipipus is a basal member of enantiornithine birds along with
Confuciusornis and shares more characters with ornithuromorphs than
previously recognized. The embryonic nature of Gobipipus specimens
sheds new light on the developmental history of enantiornithine birds.
The well-ossified bones of the fore- and hind limbs, and fusion of
many skeletal elements indicate a precocial mode of development in
Gobipipus. Apparently Gobipipus hatchlings could walk away from the
ground nests as soon as they emerged from their eggs. The asymmetry of
egg poles are unique features of Gobipipus eggs (oogenus Gobioolithus)
among Cretaceous avialans. The microstructure of the shell in
Gobioolithus eggs with the embryos of Gobipipus is typical avian (of
ornithoid basic type) and less ratite-like in morphology of the spongy
layer than is that in the other possible egg-remains of enantiornitine
birds (oofamily Laevisoolithidae).

J. K. O’Connor & N. V. Zelenkov (2013)
The phylogenetic position of Ambiortus: Comparison with other Mesozoic
birds from Asia.
Paleontological Journal 47(11): 1270-1281
DOI: 10.1134/S0031030113110063

Since the last description of the ornithurine bird Ambiortus
dementjevi from Mongolia, a wealth of Early Cretaceous birds have been
discovered in China. Here we provide a detailed comparison of the
anatomy of Ambiortus relative to other known Early Cretaceous
ornithuromorphs from the Chinese Jehol Group and Xiagou Formation. We
include new information on Ambiortus from a previously undescribed
slab preserving part of the sternum. Ambiortus is superficially
similar to Gansus yumenensis from the Aptian Xiagou Formation but
shares more morphological features with Yixianornis grabaui
(Ornithuromorpha: Songlingornithidae) from the Jiufotang Formation of
the Jehol Group. In general, the mosaic pattern of character
distribution among early ornithuromorph taxa does not reveal obvious
relationships between taxa. Ambiortus was placed in a large
phylogenetic analysis of Mesozoic birds, which confirms morphological
observations and places Ambiortus in a polytomy with Yixianornis and


Walter J. Bock (2013)
The furcula and the evolution of avian flight.
Paleontological Journal 47(11): 1236-1244
DOI: 10.1134/S0031030113110038

The presence of a short furcula in Archaeopteryx suggests that this
bird possessed a small, shortfibered, cranial portion of the pinnate
m. pectoralis originating from the furcula and possibly from the
aponeurosis between the furcula and the coracoid and cartilaginous
sternum, and inserting on the cranial edge of the humerus, and an
equally small, short-fibered pinnate caudal part of the same muscle
arising from the presumably cartilaginous sternum and inserting on the
ventral surface of the deltoid crest of the humerus. In Archaeopteryx,
the cranial-most portion of the m. pectoralis protracted the wing and
held it in place against the backward pressure, or drag, of the air
when the bird flew. There is no basis for postulating that the caudal
part of the m. pectoralis in Archaeopteryx was sufficiently large for
active flapping flight, although this presumably small muscle probably
held the wings in a horizontal position necessary for aerial
locomotion. The muscle fibers of all parts of the m. pectoralis were
short because the small distance between its origin and insertion. The
combination of features in the pectoral system of Archaeopteryx
indicates strongly that this bird was a specialized glider, not an
active flapping flier. Avian flight started from the trees downward,
not from the ground upward.