Ancient Alberta fish fossils reveal evolutionary secrets of modern species

Rare, complete fossils of ancient fish discovered in Alberta are providing new insights into the evolutionary history of freshwater fish that once thrived in North America at the end of the age of the dinosaurs. Donald Brinkman, Emeritus Researcher at the Royal Tyrrell Museum, explains that while marine fish are well-studied, freshwater fish remain poorly understood due to the scarcity of complete fossils.

The key to unlocking this knowledge lies in the unique site known as Pisces Point in central Alberta, which contains an abundance of well-preserved fish skeletons from ancient freshwater systems.

To study these delicate fossils, Dr. Lisa Van Loon and her colleagues at Western University utilized the Canadian Light Source (CLS) at the University of Saskatchewan. This powerful synchrotron facility allowed them to examine the internal structure of the fossils in unprecedented detail, despite their small size and the black rocks in which they are embedded.

By analyzing the morphology of these skeletons, the researchers were able to digitally dissect out individual parts, such as the jaw, and compare them to isolated bones found in other specimens.

The team focused on two particular groups of fish: polymixiiforms and percomorphs. Polymixiiforms, the earliest members of a group now exclusively found in deep ocean waters, were previously thought to have lived exclusively in marine environments. However, the new research reveals that these fish inhabited fresh water during the Cretaceous period, 66 million years ago. Percomorphs, a group that includes modern relatives like tuna and perch, were also found to have existed in fresh water during the same time period.

These findings, published in the Canadian Journal of Zoology, shed light on the diversity and evolutionary history of these fish groups, as well as the broader steps leading to the modern ecosystems we see today. As Dr. Brinkman notes, "It's providing information on the history of life—what were the steps leading to where we are today?" The research underscores the importance of studying these ancient freshwater fish to better understand the evolutionary pathways that have shaped the aquatic world we know today.