An entire school of tiny fish preserved in one rock

[Halichoeres]

The fossil comes from the Eocene Green River formation from the western USA, but is held in a Japanese museum. It shows 150 tiny specimens of Erismatopterus, clearly in a shoaling (schooling) formation. It's likely that fish have formed schools for a very long time, but direct evidence is very difficult to find.



Paper (open access, I believe): https://royalsocietypublishing.org/doi/10.1098/rspb.2019.0891

write-up in Science News: https://www.sciencenews.org/article/50-million-year-old-fossil-captures-swimming-school-fish

[Jose S.M.]

I read about this early. Incredible how whatever happened captured all those tiny fishes like that.

[Faelrin]

Excellently preserved fossil, but I can only wonder what led to this in the first place (aka what killed them all off).

[Halichoeres]

Yeah, good question. Theoretically an extremely rapid temperature change could do it, or a collapsing sand dune as the authors suggest, or maybe being chased into a low-oxygen or otherwise toxic section of a lake. There aren't any data on the immediate surroundings of the slab, so there's no way to test any of those hypotheses.