A Brachylophosaurus canadensis fossil femur (MOR 2598) in field jacket, showing area of sampling for... [+]
Not so long ago, finding traces of organic biomolecules in any fossil over about one million years old was thought to be an insurmountable challenge. Paleontologists never thought to look at dinosaur bones as a source of either DNA or protein sequences.
While short the half-life of DNA means it may be out of reach in dinosaurs, pioneering work by North Carolina State professor of biology Mary Schweitzer showed that protein sequences, in fact, are not. In 2009 she was able to detect proteins in an 80-million-year-old dinosaur called Brachylophosaurus canadensis, and now this find has been corroborated in a new paper lead by North Carolina State postdoctoral researcher Elena Schroeter in the Journal of Proteome Research.
Proteins are made of peptides, and the goal of these studies is to find discernible peptide sequences in dinosaur bones that have not been contaminated. With an 80-million-year-old fossil, the question of contamination is important—are these real peptide sequences that reflect ancient biomolecules of once-living dinosaurs? Or something else, like bacteria, that moved in after they died? Schroeter and Schweitzer were looking for a specific peptide sequence called collagen I, which is the most abundant protein in bone. Previous research has found this protein in a 66-million-year-old Tyrannosaurus rex fossil and an 80-million-year-old Brachylophosaurus specimen. A sensitive chemical analysis technique called mass spectrometry is used to detect these faint organic signals of ancient life.
Findings of peptide sequences in dinosaurs need to be replicated to be reliable. In this study, they use new experimental methods that are variations on ones used in the previous studies—along with a new lab set up and a freshly cleaned mass spectrometer to reduce the chance of contamination. Eight peptide sequences were recovered from the reanalysis of the Brachylophosaurus femur, with two of the same sequences recovered in both the 2009 and 2017 study, showing that these results are reproducible. "We are confident that the results we obtained are not contamination and that this collagen is original to the specimen," Schroeter says.
When these peptide sequences are placed in an evolutionary analysis, they show a close relationship to birds—exactly where a true non-avian dinosaur peptide sequence would be expected to fall. This research shows some assumptions about preservation in the fossil record might be overly cautious, as Schweitzer explains: "We've shown that it is possible for these molecules to preserve. Now, we can ask questions that go beyond dinosaur characteristics. For example, other researchers in other disciplines may find that asking why they preserve is important."
