A 67-million-year-old fossil fish discovered in Alberta, Canada, has led UC Berkeley researchers to revise the evolutionary timeline of otophysan fish, revealing that their advanced hearing system developed in the ocean before two separate migrations to freshwater. This group, which includes over 10,000 species like catfish and zebrafish, evolved sensitive ears rivaling human hearing capabilities. The findings challenge long-held assumptions about their origins.
University of California, Berkeley paleontologist Juan Liu and her team examined the fossil Acronichthys maccagnoi, a 2-inch-long specimen from the late Cretaceous Period, excavated over six field seasons starting in 2009 in Alberta, Canada. Housed at the Royal Tyrrell Museum in Drumheller, the fossil preserves a well-developed Weberian apparatus, a specialized middle ear structure that connects the air bladder to the inner ear, enhancing sound detection.
Previously, scientists believed otophysan fish, which possess this Weberian ear system, originated in freshwater around 180 million years ago on the supercontinent Pangea. However, Liu's analysis, using 3D X-ray scans and genomic data, dates their emergence to about 154 million years ago in the late Jurassic Period, after Pangea began breaking apart. The precursors to the enhanced hearing bones first appeared in marine ancestors, with full refinement occurring after two independent freshwater colonizations: one leading to catfish, knife fish, and tetras, and another to carp, minnows, and zebrafish.
"The marine environment is the cradle of a lot of vertebrates," said Liu, an assistant adjunct professor of integrative biology. "A long time consensus was that these bony fish had a single freshwater origin... My team's analysis... found completely different results: the most recent common ancestor of otophysan fish was a marine lineage and there were at least two freshwater incursions."
This system allows otophysans to detect frequencies up to 15,000 Hz, nearing the human limit of 20,000 Hz, far surpassing most marine fish limited to below 200 Hz. Simulations of the fossil's ear suggest sensitivity between 500 and 1,000 Hz, nearly matching modern zebrafish. The reinterpretation highlights how repeated freshwater entries drove speciation, explaining the group's hyper-diversity in modern freshwater ecosystems.
The study, co-authored by Michael Newbrey, Donald Brinkman, Alison Murray, and others, was published on October 2, 2025, in Science. Newbrey noted, "The new species provides crucial information for a new interpretation of the evolutionary pathways of the Otophysi with a marine origin. It just makes so much more sense." Liu's work was funded by a Franklin Research Grant from the American Philosophical Society.