When palaeontologists reported that they had recovered soft tissue from a 65-million-year-old Tyrannosaurus rex fossil, the excitement was palpable.

Without going all Jurassic Park, the discovery seemed to open the door to studying biomolecules from dinosaurs and other long-extinct creatures.

Now, however, Tom Kaye of the University of Washington says the soft material is more likely to be remnants of biofilms deposited by bacteria.

Kaye set out to find his own dinosaur tissue in bones from rocks like those that had apparently yielded the T. rex tissue.


Dental plaque

“We cracked open a lot of bones and spent hundreds of hours on an electron microscope examining them,” said Kaye. He concluded the soft material was not from dinosaurs, but from bacterial films which grew on cavities inside the bone long after the animal had died.

More familiar biofilms are thin, sticky layers like dental plaque, but Kaye says the biofilms he found produced branching hollow filaments when they coated the inside of blood vessel cavities in the bone.

Mary Schweitzer of North Carolina State University, who made the original soft tissue claim and who also reported evidence for dinosaur collagen, is not convinced.

Schweitzer points to immunological studies that show her T. rex samples were close to chicken collagen, as expected because birds evolved from predatory dinosaurs.

Original protein

Kaye, she says, “did not offer any explanation for how ‘biofilm’ proteins from dinosaur could cluster with chicken, while ‘biofilm’ from mammoth and mastodon cluster with elephant.”

That indicates at least some of the long-dead animals’ original protein survives.

It is clear that some biomarker molecules can survive for tens or hundreds of millions of years in fossils, says David Martill of the University of Portsmouth, UK. “This is why we should not abandon hope of finding fossil biomolecules,” he says.

But some of the bacterial scum could be mixed in, making the whole fossil a composite, says Dave Unwin of the University of Leicester. “That seems a lot more realistic of nature than the clean pictures presented before,” he told New Scientist.

Journal reference: PLOS-ONE (DOI: 10.1371/journal.pone.0002808)