Scientists Uncover Millions Old Fossilized School Of Fish

Fossilized School Of Fish
Image source: Proceedings of the Royal Society B

Researchers unveiled an incredible fossil which shows a fossilized school of fish and sheds light on early evidence of coordinated swimming in fish. The fossil reveals nearly 260 tiny fish swimming in coordination. The fossil is 50-million-years old, and it shows that fish have been swimming together in shoals for a very long time.

Many paleontologists dealing with ancient fossils have seen various sights in “frozen behaviors,” before, like dinosaurs in combat, migrating animals, feeding and much more. The findings published in the Proceedings of the Royal Society B, shows a fossil with such a rapid burial that it froze an entire school of fish locked in time.

The fossilized school of fish was found in a limestone slab, trapping 259 fish which came from the Green River Formation in the western U.S.  Scientists date this fossil to the period of Eocene which took place between 56 million and 33.9 million years ago. The area likely included current Colorado, Wyoming and Utah. The fossil was taken to the Fukui Prefectural Dinosaur Museum in Japan where researcher and ecologist Nobuaki Mizumoto of Arizona State University happened to see it and became interested in it, according to Science News.

When he found the fossil in 2016, Mizumoto, who is the lead author of the new study, analyzed the fossil to see whether it expressed the coordinated group behavior. The analysis could show a lot about the evolution of group dynamics and how ancient animals such as these fish interacted with one another.

The researcher classified the fish to the extinct species Erismatopterus levatus. The team measured the position and which direction each one of them was headed to understand the behavior of these fish when they were still in motion. The fossil can, however, show only a two-dimensional view of the scene, while actual shoals are present in three dimensions.

To accurately describe the behavior, the team produced almost 1,000 simulations which could predict where the next position of the shoal would be, including several factors into their analysis such as variations of water flow, spatial distribution and more.

“We inferred the position of each fish if it moved a very short distance in its heading direction from its preserved position,” the authors wrote in their study. “Each fish was then classified by whether it was now closer to its nearest neighbour (attraction) or further from it (repulsion).”

The simulations confirmed what the scientists were expecting, and that is that the fish were moving in unison. The simulations also enabled the researchers to distinguish the surroundings of their social interactions, such as the individuals were moving away from other individuals that would approach too close to them, aiming to swim toward the fish that were getting farther away. The fossilized school of fish expresses the same behaviors as modern fish swimming in swarms, which gives strong evidence that the fish expressed such dynamics since at least the Eocene period.