The fossil was taken from the Green River formation, an Eocene geologic formation that records the sedimentation in several lakes along the present-day Green River in Colorado, Wyoming, and Utah. Lake sediments are among the best to preserve fossils and other significant geological information. The Eocene epoch lasted from 56 to 33.9 million years ago, having a very variate climate.

The Diplomystus is an extinct genus of freshwater fish, very distantly related to today’s herrings. Some of the most remarkable fossils of Diplomystus were found in the Green River formation.

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