For decades a cluster of fossilised bones had drawn little attention as they sat on display in the corner of an Aussie museum. Discovered in the 1990s, the turtle shell pieces had been used in a permanent exhibition about the nation’s ancient wildlife.

But after researchers at the Museum and Art Gallery Northern Territory scraped away at the glue and plaster that had been fastening them together, they made an incredible discovery. The pieces were actually from an extinct species that had never been described before.

Dr Adam Yates, a senior curator at the museum, explained to Yahoo News more is understood about the turtles than when the bones were originally painstakingly cut from the rock and placed in the exhibition.

“Part of what stopped the shell from being re-looked was that the broken bits were glued to a base to assemble it into a moderately complete shell. And that obscured the ventral view,” he said.

“I asked for it to be taken off display and then spent months slowly and carefully chipping away the plaster base to re-expose the ventral side.”

Significant variation discovered in ancient turtle shell

Differentiating turtle species requires expertise because it often comes down to documenting tiny variations between shells, so researchers need to be able to see them from multiple angles.

“Just like human skulls, turtle shells are made of multiple bones that are sutured together. One of those bones is called the first costal, which like a lot of the shell is a modified rib,” Yates said.

Photos of the bones were sent overseas, where they were examined by US-based reptile expert Mehdi Joseph-Ouni. He identified that the bone had “complicated patterns” that were unlike those seen in other turtle species, so it was given a new name, Elseya mudburra.

Yates said, “It’s not going to mean a lot to someone who doesn’t deeply know about the anatomy of turtle shells, but it is enough for us to recognise beyond doubt that these are different from anything alive today or fossilised.”

What did the ancient turtle eat?

The turtle lived 14 million years ago in Australia’s Top End and probably became extinct as the continent became drier. It was found at the Bullock Creek fossil site where evolutionarily significant fossil marsupial, bird, lungfish and other reptile specimens have been found.

The new species is a type of Elseya or snapping turtle, which is not dissimilar to its distant cousins we see in rivers today, although it is 40 cm long and considered to be quite large. The predatory creature was likely mostly carnivorous, eating fish and crustaceans, but also the odd plant.

“The North American snapping turtle is totally different. These are northern tropical, short-necked turtles, with a powerful set of jaws,” Yates added.

Elseya mudburra was one of two new species described in the Australian Journal of Taxonomy. The other bones had also been held in the museum’s collection for several years, with their significance only now discovered. It has been named Elseya camfieldensis.