A fossil discovered near Gulgong in New South Wales, Australia, has offered researchers a detailed look into themelanosomes life of a freshwater fish that lived 15 million years ago.
The newly identified species, Ferruaspis brocksi, not only preserved its stomach contents and visible color patterns, but also includes traces of a parasite, providing an unprecedented snapshot of Australia’s Miocene ecosystems.
A Fossil That Rewrites Freshwater Fish History
The study, led by Dr. Matthew McCurry from the Australian Museum and UNSW Sydney, marks the first known fossil of a freshwater smelt in Australia. Belonging to the order Osmeriformes—which includes species like the Australian Grayling and Australian Smelt—the fossil provides rare evolutionary data for this group.
“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.”
Inside The Stomach Of Ferruaspis Brocksi
One of the most remarkable features of the fossil is its preserved stomach contents. Researchers found remains of invertebrates, primarily small phantom midge larvae, indicating the fish’s diet.
Even more unusually, a parasite—a juvenile freshwater mussel known as a glochidium—was found attached to the fish’s tail.
“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,” Dr. McCurry explained.
Coloration Preserved Through Melanosomes
The fossil also provides a rare glimpse into the external appearance of extinct aquatic vertebrates. Using high-resolution microscopy, researchers identified melanosomes, pigment-producing structures that helped reconstruct 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,” said Dr. Michael Frese from the University of Canberra and CSIRO.
This marks the first known use of melanosomes to determine coloration in a fossilized fish, a technique previously used mainly in studies of feathered dinosaurs.
A Tribute Embedded In Stone
The species name Ferruaspis brocksi reflects both its composition and a tribute to a key contributor. “‘Ferru’ comes from the Latin word ‘ferrum,’ meaning iron,” the team explained, referencing the iron-rich rocks at the site.
The second part of the name, brocksi, honors Professor Jochen J. Brocks of the Australian National University, who played a crucial role in fossil exploration at McGraths Flat.
“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,” Brocks said.
Mcgraths Flat: A Window Into Ancient Australia
McGraths Flat, located in the Central Tablelands of NSW, is classified as a Lagerstätte—a fossil site known for exceptional preservation. Fossils from this site date back 11 to 16 million years and show that the area was once a temperate rainforest rich in biodiversity.
The ongoing research at McGraths Flat, initially funded in 2017 by a descendant of famed palaeontologist Robert Etheridge, continues to yield insights into Australia’s ancient fauna.
