A newly discovered fossil from southwestern Alberta is reshaping scientists’ understanding of one of the largest groups of freshwater fish on Earth.
Researchers from the University of Western Ontario, the Royal Tyrrell Museum of Paleontology, and international partners have identified a 70-66 million-year-old, 5-centimeter-long fish as Acronichthys maccognoi – the oldest known North American member of the otophysan supergroup. This diverse group includes modern catfish, carp, and tetras, which together account for nearly two-thirds of all freshwater fish species.
“The reason Acronichthys is so exciting is that it fills a gap in our record of the otophysans supergroup,” said Dr. Neil Banerjee, earth sciences professor and co-author of the study. “It provides incredible data to help document the origin and early evolution of so many freshwater fish living today.”
Published in Science, the study used high-resolution micro-CT imaging from the Canadian Light Source in Saskatoon and the Advanced Photon Source in Illinois to examine the fossil’s intricate bone structures. These scans revealed the specialized vertebrae that allow otophysans to transmit vibrations from their swim bladder to the inner ear – a key adaptation that enhances hearing underwater.
The findings also refine the evolutionary timeline of otophysans, suggesting the group’s transition from marine to freshwater habitats occurred at least twice, with an estimated divergence about 154 million years ago – after the breakup of the supercontinent Pangea.
Now, scientists are puzzling over how Acronichthys and its relatives managed to spread across multiple continents, despite their freshwater limitations.
The discovery, supported by the Canadian Light Source – one of Canada’s largest national research facilities – adds a critical piece to the evolutionary puzzle of the planet’s most diverse group of freshwater fish.
Recent Comments