Taphonomic and Diagenetic Pathways to Protein Preservation, Part II: The Case of Brachylophosaurus canadensis Specimen MOR 2598

Abstract

Simple SummaryReports of the recovery of proteins and other molecules from fossils have become so common over the last two decades that some paleontologists now focus almost entirely on studying how biologic molecules can persist in fossils. In this study, we explored the fossilization history of a specimen of the hadrosaurid dinosaur Brachylophosaurus which was previously shown to preserve original cells, tissues, and structural proteins. Trace element analyses of the tibia of this specimen revealed that after its bones were buried in a brackish estuarine channel, they fossilized under wet conditions which shifted in redox state multiple times. The successful recovery of proteins from this specimen, despite this complex history of chemical alterations, shows that the processes which bind and stabilize biologic molecules shortly after death provide them remarkable physical and chemical resiliency. By uniting our results with those of similar studies on other dinosaur fossils known to also preserve original proteins, we also conclude that exposure to oxidizing conditions in the initial ~48 h postmortem likely promotes molecular stabilization reactions, and the retention of early-diagenetic trace element signatures may be a useful proxy for molecular recovery potential.Recent recoveries of peptide sequences from two Cretaceous dinosaur bones require paleontologists to rethink traditional notions about how fossilization occurs. As part of this shifting paradigm, several research groups have recently begun attempting to characterize biomolecular decay and stabilization pathways in diverse paleoenvironmental and diagenetic settings. To advance these efforts, we assessed the taphonomic and geochemical history of Brachylophosaurus canadensis specimen MOR 2598, the left femur of which was previously found to retain endogenous cells, tissues, and structural proteins. Combined stratigraphic and trace element data show that after brief fluvial transport, this articulated hind limb was buried in a sandy, likely-brackish, estuarine channel. During early diagenesis, percolating groundwaters stagnated within the bones, forming reducing internal microenvironments. Recent exposure and weathering also caused the surficial leaching of trace elements from the specimen. Despite these shifting redox regimes, proteins within the bones were able to survive through diagenesis, attesting to their remarkable resiliency over geologic time. Synthesizing our findings with other recent studies reveals that oxidizing conditions in the initial ~48 h postmortem likely promote molecular stabilization reactions and that the retention of early-diagenetic trace element signatures may be a useful proxy for molecular recovery potential.