Molecular tests support the viability of rare earth elements as proxies for fossil biomolecule preservation

Paul V Ullmann,Kristyn K Voegele,David E Grandstaff,Kenneth J Lacovara,Elena R Schroeter,Richard D Ash,Wenxia Zheng,Mary H Schweitzer

doi:10.1038/s41598-020-72648-6

Abstract

The rare earth element (REE) composition of a fossil bone reflects its chemical alteration during diagenesis. Consequently, fossils presenting low REE concentrations and/or REE profiles indicative of simple diffusion, signifying minimal alteration, have been proposed as ideal candidates for paleomolecular investigation. We directly tested this prediction by conducting multiple biomolecular assays on a well-preserved fibula of the dinosaur Edmontosaurus from the Cretaceous Hell Creek Formation previously found to exhibit low REE concentrations and steeply-declining REE profiles. Gel electrophoresis identified the presence of organic material in this specimen, and subsequent immunofluorescence and enzyme-linked immunosorbant assays identified preservation of epitopes of the structural protein collagen I. Our results thereby support the utility of REE profiles as proxies for soft tissue and biomolecular preservation in fossil bones. Based on considerations of trace element taphonomy, we also draw predictions as to the biomolecular recovery potential of additional REE profile types exhibited by fossil bones.

Highlights

The rare earth element (REE) composition of a fossil bone reflects its chemical alteration during diagenesis
Protein extractions resulted in two chemical extract samples for each specimen and control, an ammonium bicarbonate (ABC) extract and a guanidine hydrochloride (GuHCl) extract
Our REE data (e.g., Fig. 1) indicated a simple diagenetic history for Standing Rock Hadrosaur Site (SRHS) bones that involved a brief period of primary trace element uptake relative to many other similar-age fossils[43]

Summary

Introduction

The rare earth element (REE) composition of a fossil bone reflects its chemical alteration during diagenesis. Fossils presenting low REE concentrations and/or REE profiles indicative of simple diffusion, signifying minimal alteration, have been proposed as ideal candidates for paleomolecular investigation We directly tested this prediction by conducting multiple biomolecular assays on a well-preserved fibula of the dinosaur Edmontosaurus from the Cretaceous Hell Creek Formation previously found to exhibit low REE concentrations and steeply-declining REE profiles. Retention of endogenous isotopic signatures and early diagenetic REE profiles is predicted to be positively correlated to biomolecular preservation because each presumably requires minimal chemical alteration of bone through diagenesis (cf., Trueman and Martill31, Schweitzer[32], and references therein). Decay of the fibrous protein matrix exposes otherwise passivated (“shielded”) bone crystallite surfaces to geochemical gradients in permeating pore fluids[31,33] This molecular-level codependency forms the basis of the historical “mutual protection” theory of bone fossilization (e.g.,31,33–35)

Methods

Results

Conclusion