Science

How a 195-million-year-old dinosaur bone could still have soft tissue in it

Researchers may have found preserved organic protein in a fossilized dinosaur bone unearthed in China. Why that's a big deal. 

Transversely cut piece of the 195-million-year-old Lufengosaurus rib, the source material where the proteins were found, according to researchers. The rib is surrounded and infiltrated by light coloured sediment, while many of the vascular canals, both large and small, contain hematite, probably derived from the original blood of the living dinosaur.
Courtesy of Robert Reisz
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Caption

Fossils can be so much more than dried out, mineralized bones. Researchers have found entire creatures exquisitely preserved in amber, dinosaur eggshells, and even the fossilized structure of a 515-million-year-old animal's nervous system.

But soft tissue has largely eluded scientists. Research over the last decade has suggested that proteins may be preserved in some fossils, which could revolutionize paleontology. But the only candidates came from the very end of the age of the dinosaurs, about 70 million years ago. 

Now, a new study may be resetting that timescale, and further opening the door to a new, molecular, approach to paleontology.

Paleontologists say they've found collagen, a protein found throughout all animal bodies, preserved in the 195-million-year-old fossilized bone of a sauropodomorph dinosaur, Lufengosaurus.

And, as "collagen is a basic building block for organisms," says Robert Reisz, an author on the paper and a paleontologist at the University of Toronto Mississauga, finding ancient proteins could shine a new light on old bones.

Typically an animal's remains mineralize as they decay, so most specimens of this age consist of inorganic material, Dr. Reisz explains in a phone interview with The Christian Science Monitor. That's why finding such old organic material is particularly remarkable. Reisz and his colleagues argue that the mineral apatite that now makes up most of the bone matrix managed to protect the protein and collagen against further degradation.

They report their findings in a paper published Tuesday in the journal Nature Communications.

"It wouldn't surprise me if this type of preservation is much more common than we might think," Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved in the research, writes in an email to the Monitor. "This realization could be a game-changer for paleontologists and will give us new ways to study dinosaurs that we never before imagined."

"Jurassic Park" fans shouldn't get too excited, though, Reisz says. Preserved organic material doesn't mean there is DNA in dinosaur bones that scientists could use to clone the beasts like they do in the fictive tale. DNA has a half-life of about 521 years, according to previous research, which means that an organism's DNA would be completely destroyed within 7 million years after its death.

Still, Reisz says, collagen contains plenty of detailed information about an animal's biology and could help paleontologists fill out the picture of some of these ancient animals in life. 

But this discovery doesn't reveal new insights into Lufengosaurus, he says, as the amount of protein in this particular fossil is "miniscule." Perhaps with more advanced instruments in the future researchers will be able to glean new details from this specimen.

Reisz and his colleagues first suspected they might have some preserved organic material on their hands when they discovered fossilized embryos of Lufengosaurus a few years ago. "It looked like there were organic remains within these embryos," he recalls. But they thought it would probably be easier to identify in adult fossils.

Lucky for the team, the same site in China's Yunnan province contained a lot of adult material of Lufengosaurus. At first the researchers struggled to find anything significant, but when they cut longitudinally into some rib bones, they spotted what they were looking for: material in the tiny vascular canals within the bone. To figure out just what that tissue was, the team used synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy to identify the molecular bonds in the compounds making up the material.

Mary Schweitzer, a paleontologist at North Carolina State University, is not convinced the team has identified collagen.

Although "the method is extremely sensitive and is capable of detecting molecular bonds in extremely low concentrations," and is very specific and precise, Dr. Schweitzer writes in an email to the Monitor, "this method also has limitations."

The interactions between molecules that the SR-FTIR microspectroscopy identifies are also bonds that exist in other compounds. Yes, some of those compounds are proteins, she says, but they also crop up in "other, non protein compounds ... like glues and consolidants commonly applied to fossils in the field, or epoxies, such as the ones they embedded their material in to make the sections."

Schweitzer's own work has revealed preserved organic material in dinosaur fossils, and has been the subject of much scrutiny by other paleontologists. Her team has reported the discovery of blood cells and soft tissue preserved in dinosaur fossils. Their most recent finding, collagen in an 80-million-year-old dinosaur bone, was published last week in the Journal of Proteome Research. 

Dr. Brusatte sees Reisz's work as key support for Schweitzer's controversial research. Taken together, he says, this kind of research "tells us that soft tissues and microscopic tissues may be able to be preserved for a huge swath of time – hundreds of millions of years."

And, Brusatte adds, "If we can find these in lots of dinosaurs, we can perhaps use them to build better family trees of dinosaurs, and also to better understand the physiology and metabolism of dinosaurs." In other words, zooming in to examine fossils on the molecular level could shift how paleontologists see their enormous subjects. 

"It is always rewarding to see studies that validate our hypothesis, put forward years ago, that collagen and other endogenous biomolecules can persist across geological time," Schweitzer says. But, she adds from experience, the researchers will need to employ many other analysis techniques to confirm that what they found was actually collagen. 

Matthew Collins, a biogeochemist at the University of York whose own research focuses on old proteins, is skeptical that collagen could survive over such timescales suggested in Reisz's new paper. 

"We can predict rates of decay fairly well, and it degrades in a relatively predictable fashion," Dr. Collins writes in an email to the Monitor. The bond holding collagen together is unstable, he explains. And although dehydration can halt the breaking of this bond, it also would promote other reactions that will harm the protein's preservation. As such, he says, "we need a plausible mechanism" to explain how collagen can survive for so long. 

Reisz says he may have a clue. In the adult Lufengosaurus rib, the researchers also spotted hematite (iron oxide) particles probably derived from the decayed blood cells of the dinosaur, he says. And, as Schweitzer and her colleagues proposed that iron oxide plays a crucial role in preserving proteins, these hematite particles may be part of the solution to the puzzle.

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