Using Macro- and Microscale Preservation in Vertebrate Fossils as Predictors for Molecular Preservation in Fluvial Environments

Abstract

Exceptionally preserved fossils retain soft tissues and often the biomolecules that were present in an animal during its life. The majority of terrestrial vertebrate fossils are not traditionally considered exceptionally preserved, with fossils falling on a spectrum ranging from very well-preserved to poorly preserved when considering completeness, morphology and the presence of microstructures. Within this variability of anatomical preservation, high-quality macro-scale preservation (e.g., articulated skeletons) may not be reflected in molecular-scale preservation (i.e., biomolecules). Excavation of the Hayden Quarry (HQ; Chinle Formation, Ghost Ranch, NM, USA) has resulted in the recovery of thousands of fossilized vertebrate specimens. This has contributed greatly to our knowledge of early dinosaur evolution and paleoenvironmental conditions during the Late Triassic Period (~212 Ma). The number of specimens, completeness of skeletons and fidelity of osteohistological microstructures preserved in the bone all demonstrate the remarkable quality of the fossils preserved at this locality. Because the Hayden Quarry is an excellent example of good preservation in a fluvial environment, we have tested different fossil types (i.e., bone, tooth, coprolite) to examine the molecular preservation and overall taphonomy of the HQ to determine how different scales of preservation vary within a single locality. We used multiple high-resolution mass spectrometry techniques (TOF-SIMS, GC-MS, FT-ICR MS) to compare the fossils to unaltered bone from extant vertebrates, experimentally matured bone, and younger dinosaurian skeletal material from other fluvial environments. FT-ICR MS provides detailed molecular information about complex mixtures, and TOF-SIMS has high elemental spatial sensitivity. Using these techniques, we did not find convincing evidence of a molecular signal that can be confidently interpreted as endogenous, indicating that very good macro- and microscale preservation are not necessarily good predictors of molecular preservation.

Paleontology in the 21st Century

“…Phylogenetically and physiologically informative tissues were probed by synchrotron [ 34 ] to support the previous identification of reproductive tissues in dinosaurs [ 35 , 36 ]. Technologies continue to broaden not only the type of questions to be asked, but the type of fossils we can analyze, from coprolites [ 33 ], teeth [ 37 ], and invertebrates [ 22 , 38 , 39 ] to dinosaurs [ 25 , 34 , 40 , 41 , 42 , 43 , 44 ], mammals [ 45 ], and our own lineage [ 29 , 32 , 46 ].…”

“…Actualistic taphonomy experiments inform on the modifications introduced during diagenesis, but also informs on possible preservation conditions, recognizing that Mesozoic conditions were very different than today, and may have facilitated preservation through an elevated microbial response to high atmospheric CO 2 [ 48 ]. Additionally, although exceptionally preserved tissues have long been the target of molecular studies on fossils, there is clearly more to the story, as illustrated by Colleary et al [ 44 ], as not all exceptional fossils preserve endogenous biomolecules.…”