Along the Cedar District Formation, a geologic formation on the San Juan Islands of Washington, British Columbia, and Vancouver Island, a proximal left femur was formally recorded as the first dinosaur found in Washington state. The fossil was retrieved in the shallow marine rocks of the Campanian stage of the Cedar District formation, which means that it belongs to the Upper Cretaceous series of rocks formed 84 to 72 million years ago. It is one of only a handful of fossils uncovered from the Pacific coast of the island continent Laramidia. During the Late Cretaceous period, Laramidia was what is now known as western North America that stretches from modern-day Alaska to Mexico and most of the uncovered fossils have been found on the eastern side. There is debate on whether a segment of Baja B.C. used to be next to California and northern Mexico during this time, so uncertainty prevents assigning this fossil’s official location in Laramidia. 

Paleontologists believe the fossil belonged to a theropod: a carnivorous dinosaur of a group who are usually bipedal like humans and vary in size from small to extremely large. The reason for this conclusion is because of the cavity where bone marrow would exist and because of the attachment site of its hind leg muscles. If the femur did belong to a “tyrant lizard form” or the tyrannosauroid family, which is likely because of how big it is, it would be evidence of an earlier occurrence of its body size than previously thought to exist here.
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The First Dinosaur from Washington State and a Review of Pacific Coast Dinosaurs from North America