By John Cannon Millions of years ago, as the Indo-Australian plate pushed into the Pacific plate, a volcanic arc of islands ...

and geologists refer to this period as the Laramide Orogeny (named after the Laramie Mountains of eastern Wyoming). Geologists attribute the Laramide Orogeny to the subduction of an oceanic plate ...

The fossils were recovered from the Green River Formation, which spans parts of Utah, Wyoming, and Colorado, and were formed around the major mountain-building event called the Laramide Orogeny.