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, 10 (5), e0127792

The First Dinosaur From Washington State and a Review of Pacific Coast Dinosaurs From North America


The First Dinosaur From Washington State and a Review of Pacific Coast Dinosaurs From North America

Brandon R Peecook et al. PLoS One.


We describe the first diagnostic dinosaur fossil from Washington State. The specimen, which consists of a proximal left femur, was recovered from the shallow marine rocks of the Upper Cretaceous (Campanian) Cedar District Formation (Nanaimo Group) and is interpreted as pertaining to a large theropod on the basis of its hollow medullary cavity and proximally placed fourth trochanter. The Washington theropod represents one of the northernmost occurrences of a Mesozoic dinosaur on the west coast of the United States and one of only a handful from the Pacific coast of Laramidia during the Cretaceous. Its isolated nature and preservation in marine rocks suggest that the element was washed in from a nearby fluvial system. If the femur pertains to a tyrannosauroid, which seems likely given its size and the widespread occurrence of the group across Laramidia during Late Cretaceous times, then it would represent an earlier occurrence of large body size than previously recognized (complete femur length estimated at 1.2 meters). Uncertainty surrounding the latitude of deposition of the Nanaimo Group (i.e., the Baja-British Columbia hypothesis) precludes assigning the Washington theropod to either of the putative northern or southern biogeographic provinces of Laramidia.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Fig 1
Fig 1. Geographic overview of Late Cretaceous dinosaur assemblages from the west coast of Laramidia.
The specimen described here was collected from Campanian rocks at Sucia Island (Washington State), but these strata were probably deposited at a more southern latitude, perhaps as far south as the ‘El Gallo’ and La Bocana Roja formations of Baja California, Mexico. See Discussion for overview of specific taxa from each formation. Dinosaur assemblage data were gathered from the following sources: Matanuska Formation [–15], Northumberland Formation [16, 17], Cedar District Formation [16], Cape Sebastian Sandstone [2, 18], Chico Formation [19, 20], Budden Canyon Formation [21], Moreno Formation [22, 23], Point Loma Formation [–26], Ladd Formation [2], Rosario Formation [6], ‘El Gallo’ Formation [, , –32], La Bocana Roja Formation [33, 34]. Silhouettes modified from images available on Wikimedia Commons.
Fig 2
Fig 2. The proximal femur of a large theropod dinosaur from Washington State.
Stereopairs of UWBM 95770 in posterior (A), anterior (B) view. Proximal view (C) of UWBM 95770, with arrow indicating anterior direction. Silhouette of complete theropod femur (D) based on the tyrannosaurid Daspletosaurus torosus (TMP 2001.36.01), with corresponding portion of UWBM 95770 highlighted. Abbreviations: 4tr, fourth trochanter; in, matrix infilling of hollow marrow cavity.
Fig 3
Fig 3. Comparison of theropod dinosaur femora in posterior view.
Illustration of complete theropod femur (A), based on the tyrannosaurid Daspletosaurus torosus (TMP 2001.36.01; total length 987 mm) and (B) the Washington State theropod (UWBM 95770). Abbreviations: 4tr, fourth trochanter; dc, distal condyles; n, femoral neck; tr, area of greater trochanter (but this feature is better seen in anterior view).

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The University of Washington Burke Museum provided funding for this research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.