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Deformation in Spheroolithus dinosaur eggs from China
From: Ben Creisler
A new online paper:
Hannah M. Wilson, Christian T. Heck, David J. Varricchio, Frankie D.
Jackson & Xingsheng Jin (2013)
Evaluating deformation in Spheroolithus dinosaur eggs from Zhejiang, China.
Historical Biology (advance online publication)
Lack of stratigraphic context for dinosaur eggs inhibits understanding
of dinosaur reproductive biology and the taphonomic processes of egg
preservation. Past taphonomic work suggests two features, compression
ridges (sharp edge of broken eggshell around egg circumference) and
deformation asymmetry (proportion of crushed to rounded sides of the
egg), as geopetal structures. We examined these features across a
large sample of Spheroolithus eggs from the Cretaceous of Zhejiang,
China, to test their utility. On 103 isolated eggs, we determined
asymmetry ratios (crushed side egg height divided by rounded side egg
height) and observed an average asymmetry ratio of 0.71. Additional
observations of in situ eggs demonstrate the stratigraphic downside as
more rounded and less fractured, the stratigraphic upside as flatter
with heavier fracturing and compression ridges as parallel to original
bedding plane. Burial-caused fractures on the upper side of the egg
allowed sediment to partially fill, subsequently supporting the bottom
portion. Examining these features within 16 clutches allowed
differentiation of biotic versus taphonomically altered arrangements.
Three common clutch arrangements include planar (minimal egg overlap),
offset (extreme overlap) and agglomerate (randomly arranged, closely
packed). Analysis of egg strike and dip across clutches favours planar
clutches as the principal configuration for Spheroolithus clutches.