Washington exposed at least 18 tracks on 15 blocks in the Eocene Chuckanut Formation. The anatomy and age (about 53.7 Ma old) of the tracks suggest that the track maker was Gastornis. Although these birds have long been considered to be predators or scavengers, the absence of raptor-like claws supports earlier suggestions that they were herbivores. The Chuckanut tracks are named as the ichnotaxon Rivavipes giantess, inferred to belong to the extinct family Gastornithidae. At least 10 of the tracks are on display at Western Washington University. Feathers The plumage of Gastornis has generally been depicted in art as a hair-like covering similar to some ratites. This has been based in part on some fibrous strands recovered from a Green River Formation deposit at Roan Creek, Colorado, which were initially believed to represent Gastornis feathers and named Diatryma filifera. Subsequent examination has shown the supposed feathers were actually not feathers at all, but plant fibers. However, a second possible Gastornis feather has since been identified, also from the Green River Formation. Unlike the filamentous plant material, this single isolated feather resembles the body feathers of flighted birds, being broad and vaned. It was tentatively identified as a possible Gastornis feather based on its size; the feather measured long and must have belonged to a gigantic bird. Distribution Gastornis fossils are known from across western Europe, the western United States, and central China. The earliest (Paleocene) fossils all come from Europe, and it is likely that the genus originated there. Europe in this epoch was an island continent, and Gastornis was the largest terrestrial tetrapod of the landmass. This offers parallels with the malagasy elephant birds, herbivorous birds that were similarly the largest land animals in the isolated landmass of Madagascar, in spite of otherwise mammalian megafauna. All other fossil remains are from the Eocene; however, it is not currently known how Gastornis dispersed out of Europe and into North America and Asia. Given the presence of Gastornis fossils in the early Eocene of western China, these birds may have spread east from Europe and crossed into North America via the Bering land bridge. Gastornis also may have spread both east and west, arriving separately in eastern Asia and in North America across the Turgai Strait. Direct landbridges with North America are also known. European Gastornis survived somewhat longer than their North American and Asian counterparts. This seems to coincide with