replying to G. Mayr & A. ManegoldNature499, http://dx.doi.org/10.1038/nature12367(2013)
Our explanation that structures preserved in three Early Cretaceous Jehol birds1are ovarian follicles is challenged by Mayr & Manegold2. We believe that their conclusions are speculative and do not take into account our original arguments. Contrary to Mayr & Manegold2, 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)3and eggs are sometimes preserved in specimens of the sturgeonPeipiaosteus(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 expected4. Exceptional Jehol fossils are a reminder that simply because something is unlikely to preserve does not mean that it will not.