These small fish navigated ancient oceans during the Eocene Period, 40 million years ago, and belong to the same family as herrings and sardines. They are found in the Green River Formation, Wyoming, in the area where Lake Uintak once flourished. Volcanic or other climactic changes disrupted the lake ecology and caused a large die-off, resulting in these fossils.
These fish are preserved in the matrix in which they expired; their fossilized remains have been brushed with a transparent umber to show the fine skeletal articulation.
