Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

Abstract

Exceptionally preserved fossils are the product of complex interplays of biological and geological processes including burial, autolysis and microbial decay, authigenic mineralization, diagenesis, metamorphism, and finally weathering and exhumation. Determining which tissues are preserved and how biases affect their preservation pathways is important for interpreting fossils in phylogenetic, ecological, and evolutionary frameworks. Although laboratory decay experiments reveal important aspects of fossilization, applying the results directly to the interpretation of exceptionally preserved fossils may overlook the impact of other key processes that remove or preserve morphological information. Investigations of fossils preserving nonbiomineralized tissues suggest that certain structures that are decay resistant (e.g., the notochord) are rarely preserved (even where carbonaceous components survive), and decay-prone structures (e.g., nervous systems) can fossilize, albeit rarely. As we review here, decay resistance is an imperfect indicator of fossilization potential, and a suite of biological and geological processes account for the features preserved in exceptional fossils.

Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan

“…The contact between the lateral outer sheaths of neighboring tentacles exhibits a kink with some relief (Figures 2E and 2F). The outer sheaths appear as dark shadows in the mCT scans, indicating low density and most likely an organic composition, corroborated by their dark coloration, perhaps due to melanin or another recalcitrant pigment [47][48][49].…”

Anoxia can increase the rate of decay for cnidarian tissue: UsingActinia equinato understand the early fossil record

“…The likely BST recently described as the Qingjiang Biota, also from the Cambrian of China, preserves exquisite, abundant and diverse cnidarians (Fu et al, 2019). It is clear that decay sequence is not everything when it comes to fossil preservation merely informing on preservation potential of certain characters (Parry et al, 2018). Even with characters as unlikely to survive as anthozoan polyp tentacles, you still sometimes win the fossilisation lottery.…”

Characterization of melanosomes involved in the production of non-iridescent structural feather colours and their detection in the fossil record

“…To date, non-iridescent structural colour has not been investigated in the fossil record. It has been shown that keratin degrades during the process of fossilization [15,16]. Hence, the reliability of reconstructing non-iridescent structural colours, which are generated by keratin nanocavities in feather barbs would be impossible.…”