In a new study published in the journal eLife, an international team of paleontologists looked for preserved collagen proteins and DNA in the fossilized bones of a horned dinosaur called Centrosaurus. They didn’t find the proteins or DNA, but they did find unusual communities of modern microbes living inside the dinosaur bones.

“This is breaking new ground — this is the first time we’ve discovered this unique microbial community in these fossil bones while they’re buried underground,” said study lead author Dr. Evan Saitta, a researcher at the Field Museum of Natural History.

During the fossilization process, biological tissues degrade over millions of years, with some types of molecules breaking down faster than others. However, traces of biological material have been found inside some fossils.

While some researchers believe these could be the remains of ancient proteins, blood vessels, and cells, traditionally thought to be among the least stable components of bone, others think that they have more recent sources.

To investigate the source of the biological material in dinosaur bones, Dr. Saitta and colleagues performed a range of analyses on the 75-million-year-old fossilized bones of Centrosaurus. The bones were carefully excavated in a manner to reduce contamination.

The scientists compared the biochemical makeup of the fossils with modern chicken bones, sediment from the fossil site in Alberta, Canada, and ancient shark teeth.

They found that the Centrosaurus fossils didn’t seem to contain the collagen proteins present in fresh bones or the much younger shark teeth.

“But we see lots of evidence of recent microbes. There’s clearly something organic in these bones,” Dr. Saitta said.

“We found non-radiocarbon dead organic carbon, recent amino acids, and DNA in the bone — that’s indicative that the bone is hosting a modern microbial community and providing refuge.”

Surprisingly, these microbes aren’t quite the same run-of-the-mill bacteria living in the surrounding rock.

“It’s a very unusual community. About 30% of the sequences are related to Euzebya, which is only reported from places like Etruscan tombs and the skin of sea cucumbers, as far as I know,” Dr. Saitta said.

“We aren’t sure why these particular microbes are living in the dinosaur bones, but we’re not shocked that bacteria are drawn to the fossils.”

“Fossil bones contain phosphorus and iron, and microbes need those as nutrients. And the bones are porous — they wick up moisture. If you were a bacterium living in the ground, you’d probably want to live in a dinosaur bone.”

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Evan T. Saitta et al. 2019. Cretaceous dinosaur bone contains recent organic material and provides an environment conducive to microbial communities. eLife 8: e46205; doi: 10.7554/eLife.46205