Imagine cracking open a slab of iron-red rock and peering back 15 million years into a vibrant freshwater ecosystem teeming with life. This is exactly what a team of paleontologists did in the Central Tablelands of New South Wales, unearthing one of Australia’s most extraordinary fossil finds to date—a perfectly preserved freshwater fish fossil named Ferruaspis brocksi.
In an Australian first, researchers from the Australian Museum and UNSW Sydney, alongside colleagues from the Australian National University and the University of Canberra, have described this remarkable species in the prestigious Journal of Vertebrate Paleontology. But Ferruaspis brocksi isn’t just another ancient fish trapped in stone—it’s a fossilized snapshot of an ancient Australian rainforest ecosystem, complete with preserved stomach contents, color patterns, and even evidence of ancient parasitic relationships. This discovery opens an unprecedented window into Australia’s Miocene epoch, some 11 to 15 million years ago.
Meet Ferruaspis brocksi: The Smelt That Time Forgot
Ferruaspis brocksi belongs to the order Osmeriformes, a group of freshwater fish that includes modern-day Australian smelts and graylings. Until now, there was virtually no fossil evidence of Osmeriformes in Australia, leaving scientists to speculate when they first arrived on the continent and how they adapted to its changing landscapes over time.
“This 15-million-year-old freshwater fish fossil offers us an unparalleled opportunity to understand Australia’s ancient ecosystems,” says Dr. Matthew McCurry, lead author of the study and paleontologist at the Australian Museum and UNSW Sydney. “Without this discovery, we were largely in the dark about the evolutionary history of Osmeriformes in Australia.”
The Discovery at McGraths Flat: A Fossil Site Like No Other
The fossil was excavated from McGraths Flat, a fossil site near the town of Gulgong in NSW. This location has been hailed as one of Australia’s rare Lagerstätten—a term paleontologists use to describe fossil sites that preserve exceptional detail, including soft tissues and even cellular structures.
The iron-rich sediments of McGraths Flat proved to be the perfect preservation medium. When these fish died, their bodies sank into an oxbow lake where fine iron minerals quickly encased them, preventing decay. The result is fossil specimens so exquisitely detailed they reveal everything from stomach contents to pigmentation.
“Splitting the rust-red slabs of rock is like opening an ancient book,” says Professor Jochen J. Brocks of the Australian National University, after whom Ferruaspis brocksi is named. “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 name Ferruaspis brocksi honors both Brocks and the iron-rich rock where the fossil was found—ferrum being Latin for iron, and aspis meaning shield, reflecting the fossil’s protective casing in ironstone.
What Makes This Fossil So Special?
1. Preserved Stomach Contents: A Last Meal Frozen in Time
One of the standout features of Ferruaspis brocksi is the remarkable preservation of its last meal. The team identified partially digested phantom midge larvae—tiny aquatic insects still found in modern freshwater systems.
“We now know that these ancient fish fed on a variety of invertebrates, but phantom midge larvae appear to have been their favorite snack,” explains Dr. McCurry. “This level of detail lets us piece together the food webs that once sustained this ancient ecosystem.”
2. A Hitchhiker Parasite: Ancient Life on Ancient Life
In a rare twist, one fossil specimen shows a parasite attached to the fish’s tail—a juvenile freshwater mussel known as a glochidium. These larvae latch onto fish gills or fins, hitching rides to new locations as part of their life cycle.
“This is the first direct evidence of this type of parasitic relationship from the fossil record in Australia,” notes Dr. McCurry. “It shows us that these ancient parasitic strategies were already in place millions of years ago.”
3. Fossilized Color Patterns: The Ancient Palette
Using advanced microscopy, Dr. Michael Frese from the University of Canberra and CSIRO identified melanosomes, tiny pigment-containing structures, preserved in the fish’s fossilized skin.
“We were able to reconstruct the color pattern of Ferruaspis brocksi,” Dr. Frese reports. “It had a darker back, lighter underside, and two prominent lateral stripes along its body.” This color scheme—countershading—is still common in modern fish as a form of camouflage, making it harder for predators to spot them from above or below.
Although melanosomes have previously been used to reconstruct the colors of fossilized feathers, this marks the first time paleontologists have successfully inferred the coloration of an extinct freshwater fish species using this technique.
Why This Discovery Matters
The significance of Ferruaspis brocksi stretches far beyond the thrill of finding an ancient fish. It fills a glaring gap in Australia’s evolutionary timeline, revealing insights into:
- The arrival and diversification of Osmeriformes on the Australian continent
- The structure and biodiversity of Miocene-era rainforests in southeastern Australia
- Complex ecological interactions, including predator-prey relationships and parasitic life cycles
“The fossils at McGraths Flat are rewriting our understanding of Australia’s evolutionary history,” says Professor Kris Helgen, Director of the Australian Museum Research Institute. “This discovery is just one of many that reveal a once-lush, temperate rainforest environment rich in biodiversity—an ecosystem that has long since vanished.”
McGraths Flat: A Window into the Miocene
Between 11 and 16 million years ago, during the Miocene epoch, the Central Tablelands of New South Wales were a thriving temperate rainforest, crisscrossed by rivers and dotted with oxbow lakes. Today, the region is far more arid, but at McGraths Flat, time has stood still.
“The fossils from this site are like photographs from deep time,” says Dr. McCurry. “They show us a lush, vibrant ecosystem where fish like Ferruaspis brocksi swam alongside insects, plants, birds, and even early marsupials.”
With every slab of rock split at McGraths Flat, paleontologists are piecing together a detailed picture of this lost world—one that is helping scientists better understand how Australian ecosystems responded to climate shifts millions of years ago.
What’s Next for Paleontology in Australia?
As research continues at McGraths Flat and other sites across the continent, paleontologists are hopeful that more remarkable discoveries await. Each new find adds another brushstroke to the evolving portrait of Australia’s ancient life and its unique evolutionary journey.
For now, Ferruaspis brocksi stands as a testament to the extraordinary stories locked within stone—a reminder that even the smallest fish can tell a big story about life on Earth.
Quick Facts: Ferruaspis brocksi
- Age: Approximately 15 million years (Miocene epoch)
- Discovery site: McGraths Flat, Central Tablelands, NSW, Australia
- Preserved features: Stomach contents, color patterns, parasite attachment
- Group: Osmeriformes (related to modern Australian smelt and grayling)
- Named after: Professor Jochen J. Brocks and ferrum (iron), referring to the iron-rich rock in which it was found
Final Thoughts
As paleontologists continue their painstaking work, discoveries like Ferruaspis brocksi remind us of the resilience and adaptability of life. They also highlight the importance of preserving and studying fossil sites like McGraths Flat—a treasure trove for understanding Australia’s ancient past and its dynamic ecosystems.
“The past speaks to us in fossils,” concludes Dr. McCurry. “And when we listen carefully, we uncover stories we never imagined.”
Reference: The paleobiology of a new osmeriform fish species from Australia, Journal of Vertebrate Paleontology (2025). DOI: 10.1080/02724634.2024.2445684