Bacteria in a Dinosaur Bone Reignite a Heated Debate


EXCERPT: . . . Within pieces of fossilized bone from a newly uncovered Centrosaurus, scientists led by Evan Saitta from the Field Museum have found a thriving community of unusual bacteria. These aren’t ancient microbes, but modern ones that infiltrated the fossils and survived on the water and minerals inside them. “The bones provide a refuge,” Saitta says. They are porous, and so “have space for the microbes to proliferate. They’re full of phosphate and iron. They can wick up moisture.”

When animals die, waves of microbes consume their corpses. Scientists have looked at how this “necrobiome” changes over the hours and days after an animal perishes. But Saitta’s work suggests that microbes continue to colonize cadavers long after their flesh has decayed, after their bones have turned to stone, and after they’ve been buried several miles deep for millions of years.

That came as a huge surprise to Tullis Onstott, a microbiologist from Princeton who worked with Saitta, and who always thought of fossils as inert and inanimate. “I thought that dinosaur bone must be some kind of sealed sarcophagus,” he says. “It’s not, by any means. It’s basically a condo for bacteria. Now the question becomes: Is this true for all dinosaur bones?”

The team’s study, which has been uploaded as a preprint and has yet to be reviewed and published, complicates a heated debate that has rocked the world of paleontology for more than a decade. In the mid-2000s, Mary Schweitzer from North Carolina State University reportedly found blood vessels, cells, and traces of collagen protein from the thigh bones of two dinosaurs: a 68-million-year-old Tyrannosaurus and an 80-million-year-old Brachylophosaurus. Though a far cry from Jurassic Park, since no DNA had been discovered, the discovery was still an extraordinary one. If proteins really could survive that long, they would allow scientists to study dinosaurs at a molecular level, just as they do modern animals.

Others were skeptical. Most ancient proteins are hundreds of thousands of years old at most. A few exceptional molecules have lasted for 3 to 4 million years, protected either by exceptional cold or unique minerals. The supposed collagen from Schweitzer’s dinosaurs enjoyed no such protection, and would have been 20 to 30 times more ancient. Collagen is tough, but after such a long time, the chemical bonds that hold it together would likely have ruptured. Some critics argued that the proteins Schweitzer had detected weren’t actually there, or that the cells she had seen were actually bacterial colonies. Others suggested that the molecules and tissues must have come from modern organisms that contaminated the samples.

Schweitzer’s team addresses that last critique by taking extra care to stop external microbes from getting into its fossils. When it recently reanalyzed fragments from its Brachylophosaurus, the team even disassembled one of its analytical instruments and soaked its pieces in alcohol to kill any contaminating microbes.

But based on his new findings, Saitta now argues that such measures wouldn’t have done anything to remove microbes living inside the bones themselves. And if such microbes prove to be common, researchers must take extra steps to prove that proteins in a dinosaur’s bone actually belonged to the animal itself, and not to modern microbes that have infiltrated its remains....


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