Twenty million years ago, the giant freshwater crayfish inhabited New Zealand.

The fossil record of freshwater crayfish is surprisingly sparse, mainly containing trace fossils, some body fossils, and rarely gastroscopy. Paleontologists from Flinders University, the University of New South Wales, the Canterbury Museum and the University of Canterbury have discovered that the small molars (jaws) of the lower jaw of Gondwannan freshwater crayfish have a stiff, robust apatite layer. They discovered eight jaw fragments of a fossil freshwater crayfish that lived in New Zealand during the early Miocene period.

Prehistoric freshwater crayfish grew to about 25 cm long compared to about 8 cm of today’s New Zealand species.

“Crayfish were important creatures in ancient settings,” says Dr. Paul Scofield, senior curator at the Canterbury Museum.

“The crayfish’s body does not fossil because it is made from the wrong chemical elements. However, the molars in the jaw are made of different materials, like mammalian teeth, so they do fossil because they are made from different materials.”

“This means that we can clearly say where freshwater crayfish lived in prehistoric times. It will speak more about prehistoric ecosystems and how they worked.”

Dr. Scofield and his colleagues sifted through hundreds of thousands of small fossil fragments found near St. Batan in central Otago and used microscopes to identify prehistoric crayfish to identify each piece.

Crayfish were identified from eight jaw fragments each, about 4 mm in length.

An exciting observation was to show that the three lower jaws showed that the three types lived together.

There are currently only two species in New Zealand and live in different parts of the country.

Fragments are very rare. One distance of the 100 kg fossil fragments recovered from St. Batan produced only one fragment.

“We also identified the first fossilized Yabby buttons, which are calcium deposits that form in the stomachs of crayfish,” said Dr. Trevor Worthy, a paleontologist at Flinders University.

“Historically, paleontologists have often misidentified Yabby buttons as fossilized fish teeth.”

“Several fragments like these are sitting in boxes of museum collections around the world and are marked with question marks. Now we can say what they are.”

“Small fossils can reveal a lot about prehistoric life,” said Dr Vanessa de Petri, a paleontologist at the University of Canterbury.

“It’s not just about big sexy bones, it’s about the little things. Every piece has a story to tell.”

Team’s result It was published in Alcheringa, Australian Journal of Palaeontology.

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Trevor H. Worthy et al. Decapoda, Parastacidae, of the fossil mandible from the early Miocene of New Zealand. AlcheringaPublished online on April 13th, 2025. doi:10.1080/03115518.2025.2488056