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Jehol fossil bird ovarian follicles controversy

From: Ben Creisler

In the new issue of Nature:

Gerald Mayr & Albrecht Manegold (2013)
Can ovarian follicles fossilize?
Nature 499, E1 (11 July 2013) doi:10.1038/nature12367

ARISING FROM X. Zheng et al. Nature 495, 507–511(2013)

In a recent report Zheng et al. describe ovarian follicles in three
fossil birds from the Early Cretaceous period of China belonging to
Jeholornis and two enantiornithine species. Because these were
situated in the left half of the body cavity of the fossils, the
authors suppose that the right ovary was already reduced in these
early birds. Fossilization of ovarian follicles would constitute an
extraordinary case of soft tissue preservation, but the morphology of
the fossil structures does not agree with the ovulation mode of
coelurosaurs. There is a Reply to this Brief Communication Arising by
O'Connor, J., Zheng, X. & Zhou, Z. Nature 499,
http://dx.doi.org/10.1038/nature12368 (2013).


Jingmai O’Connor,  Xiaoting Zheng & Zhonghe Zhou (2013)
Zheng et al. reply
Nature 499, E1–E2 (11 July 2013) doi:10.1038/nature12368
REPLYING TO G. Mayr & A. Manegold Nature 499,
http://dx.doi.org/10.1038/nature12367 (2013)

Our explanation that structures preserved in three Early Cretaceous
Jehol birds are ovarian follicles is challenged by Mayr & Manegold. We
believe that their conclusions are speculative and do not take into
account our original arguments. Contrary to Mayr & Manegold,
unambiguous evidence for the preservation of less resistant tissue,
such as muscles or internal organs, are not scarce among Jehol fossils
(for example, fish, lampreys) and eggs are sometimes preserved in
specimens of the sturgeon Peipiaosteus (J.-Y. Zhang, personal
communication). Although we cannot explain the vagaries of taphonomy
that lead to the preservation of ovarian follicles in these specimens,
what is clear is that exceptional preservation of soft tissue is
dictated by the unique chemical microenvironment created by the
individual decaying tissues, and thus varied degrees of preservation
within a single specimen is expected. Exceptional Jehol fossils are a
reminder that simply because something is unlikely to preserve does
not mean that it will not.