SYDNEY: Researchers have found blood vessels and proteins in an 80-million-year-old hadrosaur fossil, strengthening evidence that tissue remains really can be extracted from such ancient fossils.
In 2005 a 68-million-year-old Tyrannosaurus rex bone was found, which appeared to contain blood vessels and cells. Two years later, researchers led by Mary Schweitzer, from North Carolina State University, in Raleigh, USA, and John Asara, from the Beth Israel Deaconess Medical Centre in Boston, claimed to have extracted collagen from the fossil (see, Protein extracted from T. rex fossil).
Collagen is one of the main structural proteins present in body tissues. The team reconstructed the protein sequence for the collagen and compared it the sequence in other species such as frogs and chickens.
Because of the controversial nature of the previous findings, the team set out to replicate them with another fossil. This time they searched for dinosaur fossils buried in deep sandstones, which were likely to be well preserved, and they speeded up the process of getting them from the field to the lab.
As they detail today in the U.S. journal Science, they hit gold in the form of a femur from a duck-billed hadrosaur, Brachylophosaurus canadensis, dug up in Montana’s Judith River formation.
“This shows that the T. rex study was not a one-hit wonder and other dinosaur fossils show preserved protein,” said Asara, “[Our] study pushes the field of molecular palaeontology… further as it shows that the ability to study fossils at the molecular level is possible.”
X marks the spot
Schweitzer said they had learnt from the earlier T. rex study where to look for environments that might be more likely to preserve protein and tissue in fossils. By looking in rocks such as iron-rich sandstones, they were able to find bones from which they could obtain and sequence proteins.
The results show “we don’t really understand as much as we thought about how cells and tissues and molecules degrade in the protected environment of bone,” said Schweitzer.
The sequences allowed the scientists to construct new family trees comparing dinosaurs with other animals such as humans, mice and alligators. They found that the B. canadensis collagen sequence was similar to the T. rex sequence they’d previously obtained, and both were in the same group as chickens and ostriches, thought to be descended from dinosaurs.
Chris Organ, a co-author from Harvard University, in Boston, U.S., said that the results were supported by other research based on the physical characteristics of both fossils and living species and the DNA of modern species.
In addition to shedding new light on how dinosaurs are related to birds, the new study vindicates the team’s previous work, which has been the subject of much controversy.
The results of the T. rex analysis were also published in Science, and lead to a number of other scientists criticising the results via letters in the same journal.
Matthew Collins, a biomolecular archaeologist at the University of York, in England, and one of the critics of the T. rex study, said that the original criticisms stemmed from the high likelihood of contamination with ancient samples, and the poor quality of data from a mass spectrometry analysis, a technique used for determining the chemical structures of molecules.
Collins said that the previous criticism had been taken into account with the new analysis, and there were much more solid results from the mass spectrometry part of the study.
“The team clearly have collagen. Now the questions shifts to, where is the collagen from?” he said. However, as the sequences are most similar to birds, and any contamination would most likely be human, that supports the idea that they are dinosaur proteins.
The flurry of criticism has actually been helpful in helping her team improve their methodology, said Schweitzer.
“The critics have such a valuable role in keeping us looking for flaws and constantly trying to improve our approaches,” she said. “As it is often said, extraordinary claims require extraordinary evidence. The claim that proteins and cells and vessels can persist over this length of time is extraordinary,” she said.