This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Rare, complete fossils of ancient fish discovered in Alberta are helping fill in the gaps in our knowledge about which freshwater fish were living in North America at the end of the age of the dinosaurs, and how they evolved into their modern descendants. Donald Brinkman, Emeritus Researcher with the Royal Tyrrell Museum, says that while much is known about saltwater (marine) fish, we still have a poor understanding of their freshwater counterparts.
"Freshwater fossils are almost all isolated individual bones like jaws, and these are very difficult to work with taxonomically," says Brinkman, who is also an adjunct professor in the University of Alberta's Department of Biological Sciences. "There are very few full skeletons, which is ideally what we want, to know what kind of fish it is and its relationship to modern groups." Fortunately, there is a site in central Alberta—appropriately named Pisces Point—that contains an abundance of complete fossil fish skeletons from ancient freshwater systems. Brinkman and his colleagues used the Canadian Light Source (CLS) at the University of Saskatchewan to uncover their secrets.
"We studied the full articulated specimens, so the whole fossilized fish was there," says Lisa Van Loon, an adjunct professor in Western University's Departments of Earth Sciences and Anthropology. These fossils are very small, just a few centimeters long, and embedded in black rocks, which makes it difficult to see much detail with the naked eye. Ultrabright synchrotron light enabled them to peer inside the fossils to learn more about their shape and internal structure, and their relationship to modern descendants.
The team's research is published in the Canadian Journal of Zoology. "It allowed us to see the morphology of the skeletons in far more detail than we otherwise could, as well as digitally dissect out individual parts like the jaw to compare with the isolated bones," said Brinkman. The researchers focused on two fish from an extraordinarily diverse group known as acanthomorphs (spiny-rayed fish), which make up around one-third of all living vertebrates.
Their modern relatives include tuna in the oceans and perch in fresh water. One is a type of fish known as a polymixiiform, the earliest member of a group that now exclusively lives in the deep ocean; this new research shows they lived in fresh water during the Cretaceous period. The other is a member of a group called the percomorphs; this study is the earliest evidence of percomorphs in the Cretaceous period.
The team's new research adds to our understanding of what life was like 66 million years ago. "These fossils have provided information about the diversity and evolutionary history of these groups of fish in particular," said Brinkman. "It's providing information on the history of life—what were the steps leading to where we are today?" Alison M.
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