Go to SchoolThis remarkable figure was just published in a paper in the Journal “Proceedings of the

Go to SchoolThis remarkable figure was just published in a paper in the Journal “Proceedings of the Royal Society”. It shows a surface in the Green River Formation – an Eocene aged deposit found largely in Wyoming, Colorado, and Utah. During the Eocene, this part of the country was filled by a series of lakes surrounded by higher peaks of the Rocky Mountains. When there was enough water, these lakes grew, but during drier periods the lakes contracted and became saltier, often killing fish and other organisms living in the water. Because the water was too salty for any scavengers to come along and eat the bodies, these fish fossils are often remarkably well preserved, even containing remnants of the skin and scales.This particular slab is about half a meter long and it contains a whopping 259 separate fossilized fish. It was recently characterized by scientists from Arizona State University, who argued that this represents a school of fish. It is unknown when fish began grouping together into schools and it is often difficult to find evidence of behavior trapped in the fossil record, so identifying a true school of fish in 50-million-year-old rocks would verify that behavior was common at least that far back in the Earth’s history. While these fish are all found together, that doesn’t verify that they were a true school while they were alive – they could have been aligned by currents after they were killed.The other parts of this figure show the additional work the scientists did – they characterized the spacing between organisms and variation in the direction that the fish were facing to see if they matched modern schooling behavior. In this case, the scientists argue that the arrangement does match modern behavior – each fish has about the amount of space they would have had if this was a school of fish swimming together. Therefore, they argue that this deposit is in fact recording an Eocene-aged school of fish.However, there are a few uncertainties – specifically the taphonomy, or the process of fossilization of this outcrop. In other words, how exactly did these fish die and how were they buried? For the fish to actually preserve the spacing they were swimming with, the school would have had to all die instantly and then be buried immediately. There is no evidence of a rapid event recorded in the available sediment, but there is also no evidence of a strong current flowing that could have aligned these fish after they died. The hypothesis of schooling behavior is supported by this find, but without knowing what killed the fish, part of the story remains missing.-JBBImage credit and original paper:https://royalsocietypublishing.org/doi/10.1098/rspb.2019.0891 -- source link

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