See in 3D

Knightia eocaena, the state fossil of Wyoming, is the most common fish from the Green River Formation and one of the most frequently collected fossil fish in the world (Grande, 1984; 2013). It is a member of the herring family, Clupeidae, and is quite similar to living herrings, although placed in a separate genus. It grew to about 25 cm, although it is usually much smaller. It is often found in mass mortalities, which indicates they formed schools. Some of these mass mortality layers are so extensive and have such a high density of fossil fish that the original schools are estimated to have contained millions of individuals (Grande, 2013). Knightia probably fed on algae, diatoms, insects, and any smaller animals it could capture. Knightia was eaten by other fish, and has been found in the jaws or stomachs of Mioplosus, Phareodus, and several other types of fossil fish. A 2022 study showed that “considerable amounts of biological residues” are found in Knightia fossils within the Green River Formation, despite the conventional age attribution of these Eocene fossils of several tens of millions of years (Misra et al., 2022). Knightia has been found in Eocene sediments in Wyoming, and in Cretaceous rocks of Antarctica and Oligocene rocks of Argentina. Similar fish from China have been classified in other genera.

Knightia close-up.

References:

Grande, L., 1984. Paleontology of the Green River Formation, with a review of the fish fauna. Geological Survey of Wyoming, Bulletin 63, p. 333. (1st ed. 1980.)

Grande, L., 2013. The lost world of Fossil Lake: Snapshots from deep time. University of Chicago Press. p. 425.

Misra, A.K., Rowley, S.J., Zhou, J., Acosta-Maeda, T.E., Dasilveira, L., Ravizza, G., Ohtaki, K., Weatherby, T.M., Trimble, A.Z., Boll, P. and Porter, J.N., 2022. Biofinder detects biological remains in Green River fish fossils from Eocene epoch at video speed. Scientific Reports, 12(1), p. 10164. doi:10.1038/s41598-022-14410-8.