Sediment‐encased maturation: a novel method for simulating diagenesis in organic fossil preservation

Abstract

Exceptional fossils can preserve diageneticallyaltered biomolecules. Understanding the pathways that lead to such preservation is vital to utilizing fossil information in evolutionary and palaeoecological studies. Experimental taphonomy explores the stability of tissues during microbial/ autolytic decay or their molecular stability through maturation under high pressure and temperature. Maturation experiments often take place inside sealed containers, preventing the loss of labile, mobile or volatile molecules. However, wrapping tissues inside aluminium foil, for example, can create too open a system, leading to loss of both labile and recalcitrant materials. We present a novel experimental procedure for maturing tissues under elevated pressure/temperature inside compacted sediment. In this procedure, porous sediment allows maturation breakdown products to escape into the sediment and maturation chamber, while recalcitrant, immobile components are contained, more closely mimicking the natural conditions of fossilization. To test the efficacy of this procedure in simulating fossil diagenesis, we investigate the differential survival of melanosomes relative to proteinaceous tissues through maturation of fresh lizard body parts and feathers. Macro-and ultrastructures are then compared to fossils. Similar to many carbonaceous exceptional fossils, the resulting organic components are thin, dark films composed mainly of exposed melanosomes resting on the sediment in association with darkened bones. Keratinous, muscle, collagenous and adipose tissues appear to be lost. Such results are consistent with predictions derived from non-sediment-encased maturation experiments and our understanding of biomolecular stability. These experiments also suggest that organic preservation is largely driven by the original molecular composition of the tissue and the diagenetic stability of those molecules, rather than the tissue's decay resistance alone; this should be experimentally explored in the future.

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

“…Further, Saitta et al . () reported loss of keratinous tissues in feather barbs experimentally matured in sediment. The pellets and barb imprints were not tested for chemical evidence of keratin or its residues (Saitta et al .…”

“…). These findings have been disputed on the basis of recent taphonomic experiments on feathers (Saitta et al . 2017 a – b , 2019).…”

“…It has been proposed that maturation of tissues in Al foil packets may result in the potential loss of labile and recalcitrant materials (Saitta et al . ). While loss of volatiles (gases and water) may occur in this scenario, previous experiments demonstrate that more recalcitrant materials (including melanosomes and the surrounding keratinous matrix) can survive maturation (McNamara et al .…”

“…One criticism of maturation in sealed Au capsules is that these may prevent loss of labile materials (Saitta et al . ). In natural systems, however, confining sediment may prevent at least localized loss of labile materials from tissues.…”

Raman Spectroscopy Detects Amorphous Carbon in an Enigmatic Egg From the Upper Cretaceous Wido Volcanics of South Korea

“…The accuracy of the estimated paleotemperature would be a potential future research avenue because thermal maturity assessment has been mostly focused on the marine microfossil (see section "Introduction" above), but to our knowledge, few study has focused on thermal maturity of terrestrial macrofossil. A systematic taphonomic experiment that controls temperature and/or pressure would be also helpful for such an approach (e.g., Saitta et al, 2019a).…”