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The Arctic landscape during the Cretaceous Period may have been dominated by the dinosaurs, but the rivers and streams held something more familiar.
Alaska’s fresh waters 73 million years ago were teeming with the ancient relatives of today’s salmon, pike and other northern fish. A new paper published this week in the journal Papers in Palaeontology has named three new species of fish from that time period, including a salmonid, dubbed Sivulliusalmo alaskensis.
“This is not only a new species; it’s the oldest salmonid in the fossil record,” said Patrick Druckenmiller, director of the University of Alaska Museum of the North and the paper’s senior author. The paper also documents multiple other species of ancient fish new to the Arctic, including two new species of pike and the oldest record of the group that includes carp and minnows.
“Many of the fish groups that we think of as being distinctive today in the high-latitude environment in Alaska were already in place at the same time as dinosaurs,” he said.
The discovery of Sivulliusalmo alaskensis — the genus is named from the Inupiaq and Latin words for “to be first” and “salmon,” respectively — adds another 20 million years to the fossil history of the salmon family. Previously, the oldest salmonid documented was in fossils found in British Columbia and Washington.
It’s notable that salmonids, which tend to prefer colder water, were thriving even during the warmth of the Cretaceous, and that they lived for millions of years in regions that have gone through dramatic changes in geography and climate, said Andrés López, curator of fish at the UA Museum of the North and a co-author of the paper.
Despite it being warmer in the Arctic at that time, there would have still been big seasonal swings in temperature and light, just like there are today, he said.
“Salmon were already the kind of fish that do well in a place where those dramatic shifts were happening,” López said. “Despite all of the changes that the planet has gone through, all of the changes in the geography and the climate, you still had the ancestors of the same groups of species that dominate the fresh waters of the region today.”
The new species are the latest discovery to come from the Prince Creek Formation, which is famous for dinosaur fossils found at a series of sites along the Colville River in northern Alaska. In the Cretaceous, Alaska was much closer to the North Pole than it is today. For more than a decade, UAF scientists have been poring over thousands of sometimes microscopic fossils to paint a picture of a polar ecosystem during the age of the dinosaurs, including mammals, birds, and fish.
“These types of fossils are often overlooked,” Druckenmiller said. He and his colleagues intentionally aim to recover all the vertebrate fossils available, no matter how small.
“You couldn’t begin to understand a modern Arctic ecosystem without understanding the smallest animals that live there,” he said. The same is true for ancient ecosystems.
Fish fossils are one of the most abundant types of fossils at the Prince Creek Formation, Druckenmiller said, but they are very difficult to see and distinguish in the field. So, the scientists hauled buckets of fine sand and gravel back to their museum lab, where they used microscopes to find the bones and teeth.
The findings in the current paper are primarily based on tiny, fossilized jaws, some of which would easily fit on the end of a pencil eraser, Druckenmiller said. To get a good look at the fossils, members of the research team from Western University in Ontario and the University of Colorado Boulder used micro-computed tomography to digitally reconstruct the tiny jaws, teeth and other bones.
“We found a really distinct jaw and other parts that we recognized as a member of the salmon family,” he said.
The presence of salmonids in the Cretaceous polar regions and the absence of common lower-latitude fish from this same time period indicate that the salmon family likely originated in the North, Druckenmiller said. “Northern high latitude regions were probably the crucible of their evolutionary history.”
The lead author of the paper is Donald Brinkman of the Royal Tyrrell Museum of Palaeontology. Other UAF co-authors include Lauren Wilson and Zackary Perry. Scientists from Florida State University, the University of Colorado, Princeton University, Western University and LISA CAN Analytical Solutions Inc. also co-authored the paper.
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