A team of scientists led by Dr. Matthew McCurry from the Australian Museum and UNSW Sydney unveiled the discovery of a previously unknown species of 15-million-year-old fossilized freshwater fish named Ferruaspis brocksi. This find, excavated from the McGraths Flat fossil site in the Central Tablelands of New South Wales, represents the first fossil evidence of freshwater smelts (order Osmeriformes) in Australia.
Before this discovery, scientists were unable to determine precisely when the Osmeriformes group of fish appeared in Australia or how they evolved over time. The exceptional preservation of Ferruaspis brocksi provided unprecedented insights into the behavior and ecology of ancient fish during the Miocene epoch.
"The discovery of a 15-million-year-old fossil of a freshwater fish gives us a unique opportunity to study ancient ecosystems of Australia and understand the evolution of fish during the Miocene epoch," the researchers stated.
One of the most striking aspects of the fossil is the preserved stomach contents, which offer a direct window into the diet of this ancient species. "We now know that they fed on invertebrates, with small larvae of ghost midges (insects from the family Chaoboridae) being the main food source," said McCurry.
In addition to its stomach contents, the fossilized fish exhibits a distinct pattern of coloration. Dr. Michael Frese, a researcher from the University of Canberra and CSIRO, noted that they could determine the fish's coloration by examining tiny structures preserved in the fossil. "Using a powerful microscope, we were able to see tiny color-producing structures known as melanosomes. Fossilized melanosomes have previously enabled paleontologists to reconstruct the color of feathers, but melanosomes have never been used to reconstruct the color pattern of a long extinct fish species," said Frese.
"The fish was darker on its dorsal surface, lighter in color on its belly, and had two lateral stripes running along its side," Frese added. This coloration pattern suggests that Ferruaspis brocksi may have used counter-shading as a form of camouflage, much like many modern fish species.
The scientists also discovered a parasite on one of the fossils—a young freshwater mussel called a glochidium. This parasite attaches to a fish's tail to move downstream, providing information about symbiotic relationships in ancient ecosystems.
The naming of Ferruaspis brocksi holds special significance. Ferruaspis is derived from the Latin word "ferrum," meaning "iron," referencing the iron-rich rock in which the fossil was found. The species name "brocksi" honors Professor Jochen J. Brocks from the Australian National University, who played a pivotal role in the discovery. "Collecting fossils at McGraths 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. 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," said Brocks.
McCurry highlighted the broader significance of the find. Osmeriformes are a diverse group of fish in Australia today, including species like the Australian Grayling and the Australian Smelt. However, fossil records of these fish have been scarce. "The fossils formed between 11 and 16 million years ago and provide a window into the past. They prove that the area was once a temperate wet rainforest and that life was rich and abundant in the Central Tablelands, New South Wales," said McCurry.
The McGraths Flat site, where the fossil was discovered, has yielded a wealth of fossils, including spiders, insects, and plants, expanding our understanding of ancient environments. It is one of only a handful of fossil sites in Australia classified as a Lagerstätte—a site that contains exceptionally preserved fossils with remarkable detail.
The Miocene Epoch, spanning from approximately 23 to 5 million years ago, was a period of change in Australia, characterized by a rich diversity of plant and animal life. Around 14 million years ago, an abrupt climate shift known as the "Middle Miocene Disruption" led to widespread extinctions. As the continent gradually became more arid, lush rainforests gave way to the dry shrublands and deserts familiar today.
The article was written with the assistance of a news analysis system.