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Iteravis (ornithuromorph bird) osteohistology (free pdf)
A new paper:
Jingmai K. O'Connor, Min Wang, Shuang Zhou, and Zhonghe Zhou (2015)
Osteohistology of the Lower Cretaceous Yixian Formation ornithuromorph
(Aves) Iteravis huchzermeyeri.
Palaeontologia Electronica 18.2.35A: 1-11
We describe for the first time the histology of an ornithuromorph bird
from the Lower Cretaceous Jehol Group, revealing the bone structure of
one of the oldest members of this derived clade. The newly discovered
Sihedang locality of the Yixian Formation in northeastern China
preserves the oldest ornithuromorph dominated avifauna, with all
collected birds referable to a single taxon, Iteravis huchzermeyeri.
These specimens are all preserved in a relatively greater degree of
three-dimensionality compared to Jehol specimens from other
localities. We sampled a specimen of Iteravis in order to test the
hypothesis that this aggregation of birds may represent a breeding
colony. Although medullary bone is known to facilitate
three-dimensional preservation, this bone tissue was not present in
the histological samples. The specimen is nearly adult with regards to
skeletal fusion, and histology indicates medullary expansion had
occurred and an inner circumferential layer had already formed.
However, lines of arrested growth are absent. Overall the bone
histology is comparable to Ichthyornis; this is consistent with the
derived phylogenetic placement inferred for this new taxon relative to
previously sampled basal ornithuromorphs (Patagopteryx, Hollanda),
which all indicate they required more than one year to reach
adulthood. This suggests that the modern avian growth strategy evolved
in the Early Cretaceous in non-ornithurine birds.