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50 million year old fossil shows a school of baby fish in their last moments

This 50 million year old fossil, in the possession of a museum in Japan, shows 259 fish swim in a school — one of the earliest known examples of coordinated group behavior ever.
(Mizumoto et al./Proceedings of the Royal Society B)

One fish, two fish, dead fish, cool fish.

There is space for all the species in a newly described fossil that shows 259 baby fish swimming together in a school, about 50 million years ago. According to the authors of a study published Wednesday (May 29) in the journal Proceedings of the Royal Society B, this ex-school may be the oldest known fossil evidence that the prehistoric fish swam in unison, just as modern fish do today.

A team of researchers from Arizona stumbled across this peculiar rock during a visit to the Oishi Fossils Gallery of Mizuta Memorial Museum in Japan. Working with the museum, the researchers determined that the fish fossil probably originated in America, the Green River Formation, a geological layer, the current Colorado, Wyoming and Utah, which contains a wealth of fossils from between 53 million and 48 million years ago.

The fish in question all belonged to the extinct species Erismatopterus levatus, and were apparently locked together in the middle of a routine swim, if that is interrupted by an underwater avalanche of sand, the researchers wrote. Two of the little monsters were swimming in the same direction and in a tight formation.

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To prove that the fish were indeed swimming in a school and not just petrified that way by coincidence, the researchers ran a series of simulations to reproduce the group of likely movements. The simulations showed that the fish were apparently not to swim alone in choir, but also did so according to a timeless set of rules of conduct that still is today.

“We found traces of two rules for social interaction similar to those used by existing fishing: divestment of close to individuals, and attraction in the direction of the neighbors at a distance,” the researchers wrote in their study. In other words, the individual fish swam close together, but not so close that they crashed.

According to the authors of these old slab of dead swimmers shows that fish (and other animals) have developed group behaviors at least 50 million years ago. This synchronized swimming seems to have stored, the fish is eaten by a predator, even if it could not save them from an exhibition in the museum.

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Originally published on Live Science.

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