Tiny Fish Fossil Sheds Light on Freshwater Evolution

Quick Smiles:

• A new prehistoric fish fossil, Acronichthys maccagnoi, helps clarify the evolution of catfish, carp, and tetras.
• The fossil, found inland in Alberta, is the oldest North American member of its supergroup.
• Advanced 3D scanning has safely revealed delicate skeleton details for scientists.

The discovery of a small fossilized fish in southwestern Alberta, Canada, is offering researchers fresh clues about the ancient origins of otophysans—a powerful lineage ahead of catfish, carp, and tetras found in rivers and lakes worldwide. The fossil, from the Late Cretaceous and measuring just 1.6 inches, was described as a completely new species based on studies from Western University and the Royal Tyrrell Museum of Paleontology.

Professor Neil Banerjee shared,

“The reason Acronichthys is so exciting is that it fills a gap in our record of the otophysans supergroup. It is the oldest North America member of the group and provides incredible data to help document the origin and early evolution of so many freshwater fish living today.”

Experts learned that otophysans evolved from marine to freshwater several times in history, with this fossil pushing the divergence from saltwater to freshwater species to at least 154 million years ago. Researchers are curious how early freshwater fish like Acronichthys could have traversed across continents while staying away from salty oceans, as their modern relatives are found nearly everywhere except Antarctica.

Curator emeritus Don Brinkman remarked,

“There’s still so much we don’t know, and a fossil site right here in Canada is giving us the key to understanding the origins of groups that now dominate rivers and lakes around the world.”

Special technology helped study the fragile fossil, with earth sciences Professor Lisa Van Loon using synchrotron beam-lines and micro-CT scans to view the structure in sophisticated 3D without harming it.

Van Loon explained,

“Many of the fossil specimens collected by the Royal Tyrrell Museum are incredibly fragile, and some are impossible to extract from the rock itself, so micro-CT scans provide not only the best method for acquiring detailed images of what’s inside, they’re also the safest way to avoid destroying the fossil all together.”

Brinkman concluded,

“Dinosaurs are pretty exciting, so a lot of time and effort has been focused on them… but we’ve only scratched the surface when it comes to understanding the diversity of prehistoric freshwater fish.”

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