THE FIRST RECORD OF DINOSAUR TRACKS IN THE STATE OF WASHINGTON, USA

Dinosaur remains from the western shoreline of Laramidia (near the modern-day Pacific Coast of North America) are rare and often isolated and/or fragmentary. The majority of the finds come from the regions of Baja, Mexico and nearby southern California, with only a handful of dinosaur-bearing localities from central California to coastal Alaska. To date, the State of Washington has only produced one dinosaur fossil: a partial proximal left femur from a theropod recovered from the Upper Cretaceous (Campanian) Cedar District formation of the Nainamo Group at Sucia Island State Park.

Here we report the discovery of the first dinosaur track site from the State of Washington. The locality is along the eastern flank of the Cascade Mountains near the city of Ellensburg, and it consists of a series of buff sandstones and dark gray-to-black shaley mudstones exposed along a road cut. The dinosaur tracks are preserved as sand infills (natural hypichnial casts) atop the shaley mudstones in which the prints were made. Three dinosaur groups are represented by two complete and three partial tracks: one partial theropod pes, two partial and one complete ornithopod pes, and one complete ankylosaur pes with detailed skin impressions.

The locality’s strata are assigned to the Upper Cretaceous on the basis of an isolated mosasaur tooth crown from a shale unit directly beneath the track-bearing sandstone. The recovery of this tooth also represents the first occurrence of mosasaur fossils from the State of Washington and confirms a marine depositional environment for the shale units. In addition to dinosaur tracks, sandstone layers contain cross-beds, ripple marks, worm burrows, and terrestrial plant material including both woody tissue and leaves. Frequent alternations of shale and sandstone indicate a dynamic nearshore environment.