Two recent studies suggest that it is possible to isolate protein fragments from dinosaurs much further back in time than ever thought possible. The first one, led by Mary Schweitzer
who became famous (and questioned) for the discovery of 'intact' soft tissue in T-Rex bones back in 2007, confirms a highly controversial claim to have recovered 80-million-year-old dinosaur collagen. And the second one even suggests that the protein may have survived in the 195-million-year-old remains of Lufengosaurus
sciencemag.org wrote:Last week in the Journal of Proteome Research, Schweitzer, her postdoct Elena Schroeter, and colleagues report that they did a complete makeover of their 2009 experiment to rule out any possible contamination. They took new samples from the same 80-million-year-old fossil, of a duck-billed dinosaur called Brachylophosaurus canadensis. They reworked procedures for extracting would-be proteins from the bone, identified protein fragments with a more sensitive mass spectrometer, and compared the recovered protein sequences to those from many more living animals. Schroeter even went so far as to break down the mass spectrometer piece by piece, soak the whole thing in methanol to remove any possible contaminants, and reassemble the machine. “About the only thing that is the same [as the 2009 experiments] is the dinosaur,” Schweitzer says.
In their 2009 paper Schweitzer’s team had identified three fragments of a protein called collagen 1 from their fossil. Collagen is the main protein in connective tissue and is abundant in bone. Each fragment contained about 15 amino acids strung together, which the mass spectrometer was able to identify. In their current study, Schweitzer’s team identified eight protein fragments, two of which matched those identified originally. “If [both sets] are from contamination, that’s almost impossible,” Schweitzer says.
The three protein fragments originally recovered most closely resembled the collagen found in living alligators and other reptiles. But the new data show that B. canadensis collagen was a better match to that of birds. That’s just what paleontologists, who consider birds to be descendants of extinct dinosaurs, would predict.
Just how those collagen sequences survived tens of millions of years is not clear. Schweitzer suggests that as red blood cells decay after an animal dies, iron liberated from their hemoglobin may react with nearby proteins, linking them together. This crosslinking, she says, causes proteins to precipitate out of solution, drying them out in a way that helps preserve them. That’s possible, Collins says. But he doesn’t think the process could arrest protein degradation for tens of millions of years, so he, for one, remains skeptical of Schweitzer’s claim. “Proteins decay in an orderly fashion. We can slow it down, but not by a lot,” Collins says.
In the case of the 195-million-year-old Lufengosaurus
-proteins, a team led by Robert Reisz
from the University of Toronto
reports a finding what they believe is collagen in a 195-million-year-old fossil rib. Reisz
says his team's methods, called Raman spectroscopy
and synchrotron radiation Fourier transform infrared microspectroscopy
(SR-FTIR), can probe the chemical makeup of a sample without the need to purify it first, which lowers the risk of contamination. The rib absorbed infrared light in wavelengths that match those of collagen from modern animals.
sciencemag.org wrote:Schweitzer and Cappellini caution that while SR-FTIR is good at spotting the so-called amide chemical bonds that link successive amino acids in proteins, it can’t pin down exactly which protein is present, or the protein's sequence. Thus it isn't useful for evolutionary studies. This method also can’t rule out that the amide bonds are in other compounds, such as the epoxy used to assemble microscope slides. “Synchrotron data is very powerful, but it’s limited,” Schweitzer says. “I would like to have seen confirmatory evidence,” such as exposing the fossilized material to an antibody that binds solely to collagen to see whether it targeted the fossilized material. Reisz agrees “that certainly would be the next step.” But he’ll have to team up with other specialists to carry that out.
Still, his work, too, suggests that collagen fragments can survive for astonishing periods of time. Meanwhile, Schweitzer’s team is going beyond collagen. In a 2015 paper in Analytical Chemistry, her group reported isolating fragments of eight other proteins from fossils of dinosaurs and extinct birds, including hemoglobin in blood, the cytoskeletal protein actin, and histones that help package DNA. Comparing those sequences from many different species could reveal evolution’s handiwork over geological time, much as studies of ancient DNA do today.
Although this certainly isn't Jurassic Park
, in which we recreate creatures that existed millions of years ago, their work is now about to open the door to more in-depth study of long extinct species.