Stomach contents preserved after 15 million years in fish fossil

Scientists have identified a new fossil species of freshwater fish, Ferruaspis brocksi, from a site near Gulgong, in NSW, Australia.

This discovery, led by Dr. Matthew McCurry from the Australian Museum and UNSW Sydney, provides a rare glimpse into Australia’s ancient aquatic life.

The fossil, which is estimated to be 15 million years old, preserves both the fish’s stomach contents and its color patterns. The Journal of Vertebrate Palaeontology has published the findings.

Ferruaspis brocksi belongs to the Osmeriformes order, which includes species like the Australian Grayling and Australian Smelt.

It is the first freshwater smelt fossil found in Australia. The species was named in honor of Professor Jochen J. Brocks from the Australian National University, who contributed to fossil discoveries at McGraths Flat.

Tracing the evolution of Osmeriformes

Dr. McCurry emphasized that before the discovery of this fossil, scientists lacked evidence to confirm when Osmeriformes first arrived in Australia.

“The discovery of the 15 million-year-old freshwater fish fossil offers us an unprecedented opportunity to understand Australia’s ancient ecosystems and the evolution of its fish species, specifically the Osmeriformes group during the Miocene epoch, 11-15 million years ago,” McCurry said.

Without fossils, researchers could not determine whether these fish had evolved significantly over time. This new find provides crucial evidence for understanding how they adapted to ancient Australian waters.

What did the fish fossil reveal?

The well-preserved fossil reveals fascinating details about the fish’s diet. The stomach contents show that it fed on various invertebrates, mainly small phantom midge larvae.

This level of preservation is rare and helps scientists reconstruct past ecosystems with greater accuracy.

“One of the fossils even shows a parasite attached to the tail of the fish. It’s a juvenile freshwater mussel called a glochidium. These juvenile mussels attach themselves to the gills or tails of fish to hitch rides up and down streams,” McCurry added.

The species’ name reflects its discovery in iron-rich rock. “Ferru” comes from the Latin word “ferrum,” meaning iron, while “brocksi” honors Professor Brocks.

Honoring a scientific contribution

Professor Brocks expressed excitement about having this fossil species named after him.

“Collecting fossils at McGrath Flat is a highlight for me every year. Splitting the rust-red slabs of rock is like opening an ancient book, revealing the creatures that inhabited an Australian oxbow lake some 15 million years ago,” exclaimed Professor Brocks.

“This little fish is one of the most beautiful fossils there, and finding the first vertebrate among the abundant plant and insect fossils was a real surprise. Having F. brocksi named after me is a real joy.”

The McGraths Flat fossil site continues to provide remarkable insights into prehistoric life, and contributes to a better understanding of Australia’s ecological past.

Revealing the fish’s coloration

Dr. Michael Frese from the University of Canberra and CSIRO highlighted another exciting aspect of the research – the ability to determine the fish’s color pattern.

“The fish was darker on its dorsal surface, lighter in color on its belly and had two lateral stripes running along its side,” Dr. Frese said.

Using a powerful microscope, scientists identified melanosomes, which are tiny structures responsible for producing color.

While melanosomes have helped reconstruct the colors of ancient feathers, this is the first time they have been used to determine the color pattern of a long-extinct fish.

Site of exceptional fossil preservation

Professor Kris Helgen, Director and Chief Scientist at the Australian Museum Research Institute, praised the ongoing research at McGraths Flat.

“Dr. Matt McCurry’s work at the McGraths Flat fossil site has been outstanding. This is one of many discoveries made at this site, which continues to play a significant role in advancing our understanding of Australia’s evolution during the Miocene era.”

McGraths Flat is one of the rare fossil sites in Australia classified as a “Lagerstätte” – a site with exceptionally well-preserved fossils.

Located in the Central Tablelands of NSW, it offers a unique window into an ancient rainforest ecosystem.

What do fish fossils reveal about ancient Australia?

Dr. McCurry explained that fossils from this site, dating back 11 to 16 million years, show that the region was once a temperate, wet rainforest teeming with life.

These discoveries help scientists reconstruct ancient landscapes and understand the biodiversity of prehistoric Australia.

The initial McGraths Flat expedition in 2017 received funding from a descendant of Robert Etheridge, a renowned English palaeontologist who played a crucial role in developing the Australian Museum’s collections.

Etheridge launched a series of scientific expeditions that continue today, ensuring that Australia’s rich fossil heritage remains a key focus for researchers.

The discovery of Ferruaspis brocksi is another milestone in understanding how ancient species thrived and adapted in Australia’s evolving landscapes.

The study is published in the Journal of Vertebrate Paleontology.

Image Credit: Salthy Dingo

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