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Psittacosaurus bonebed from Yixian Formation (Lower Cretaceous), Liaoning, China

Ben Creisler

A new paper:

Brandon P. Hedrick, Gao Chunling, Gomaa I. Omar, Zhang Fengjiao, Shen
Caizhi & Peter Dodson (2014)
The osteology and taphonomy of a Psittacosaurus bonebed assemblage of
the Yixian Formation (Lower Cretaceous), Liaoning, China.
Cretaceous Research 51: 321–340
DOI: 10.1016/j.cretres.2014.06.015

We present the first detailed description of the osteology and
mineralogy of an assemblage of Psittacosaurus juveniles (DMNH D2156)
associated with a larger specimen from the Lujiatun beds of the Yixian
Formation in Liaoning, China. We fully describe all of the material as
well as discuss intraspecific variation in the sample set of
twenty-four juveniles with associated postcranial material and compare
with previously described ceratopsian juvenile material. Based on the
development of the ends of long bones, it is suggested that the
juveniles are not embryonic, but are post-hatchlings. In comparison
with previous histologic analyses on P. lujiatunensis, it is shown
that the large specimen associated with the juveniles is likely not
yet an adult and that this assemblage is not an exemplar of parental
care, but may be an example of post-hatching cooperation. The large
specimen is however, shown to be positively associated with the
assemblage and was not added on after excavation. Additionally, an
allometric analysis of Psittacosaurus bone lengths is performed in
order to determine ontogenetic trajectories and allometry using femur
length as a proxy. This demonstrates that the vast majority of long
bones and girdle elements in Psittacosaurus are isometric with body
size, but supports previous analyses that the forelimb grew slower
than the hindlimb. Finally, a mineralogical analysis using X-ray
diffraction and petrographic thin sections of the block where DMNH
D2156 is preserved shows that the animals were preserved in a
volcanic-lithic arenite. The statistically significant alignment of
specimens and preservation in a volcanic rock suggests that the
taphonomic setting and reasoning for the exceptional preservation of
the specimen is due to burial by a volcaniclastic debris flow. The
vast majority of specimens in the Yixian Formation are found in
lacustrine strata, recently suggested to be carried into lakes by
pyroclastic debris flows. The preservation of DMNH D2156 in a clastic
flow further supports the volcaniclastic flow preservation model for
the fauna of the Yixian Formation, but we prefer a lahar flow
interpretation for DMNH D2156 since there is no evidence of the bone
microstructure being affected by intense heat associated with
pyroclastic debris flows.