Paleontologists have found the fossils of three new fish species — including the earliest known salmonid fish, Sivulliusalmo alaskensis — at the Prince Creek Formation of northern Alaska, the United States.

“Sivulliusalmo alaskensis is not only a new species, it’s the oldest salmonid in the fossil record,” said Dr. Patrick Druckenmiller, director of the University of Alaska Museum of the North.

“Our paper also documents multiple other species of ancient fish new to the Arctic, including two new species of pike — Archaeosiilik gilmulli and Nunikuluk gracilis — 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.”

The discovery of Sivulliusalmo alaskensis 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 Dr. Andrés López, curator of fish at the University of Alaska Museum of the North.

“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.”

“Salmon were already the kind of fish that do well in a place where those dramatic shifts were happening.”

“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.

“Fish fossils are one of the most abundant types of fossils at the Prince Creek Formation, but they are very difficult to see and distinguish in the field,” Dr. Druckenmiller said.

“So, we hauled buckets of fine sand and gravel back to our museum lab, where we used microscopes to find the bones and teeth.”

“Our new findings are primarily based on tiny, fossilized jaws, some of which would easily fit on the end of a pencil eraser.”

To get a good look at the fossils, the authors 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,” Dr. Druckenmiller 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.”

“Northern high latitude regions were probably the crucible of their evolutionary history.”

The paper was published in the journal Papers in Palaeontology.

_____

Donald B. Brinkman et al. 2025. Fishes from the Upper Cretaceous Prince Creek Formation, North Slope of Alaska, and their palaeobiogeographical significance. Papers in Palaeontology 11 (3): e70014; doi: 10.1002/spp2.70014