Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 38-4
Presentation Time: 9:00 AM-3:30 PM


RETALLACK, Gregory J., Department of Earth Sciences, University of Oregon, 1275 E. 13th Ave, Eugene, OR 97403

Before October 2018, there were no confirmed dinosaurs from the state of Oregon, but by the end of that month there were two. One of these is a toe bone of a large (5.1 m long and 678 kg live weight) ornithopod from near Mitchell, Oregon, found by Greg Retallack. Associated ammonites give a very precise age of about 103 Ma (early Albian, Early Cretaceous), and also indicate that it was from a disintegrating carcass that drifted out into the ocean. The Mitchell ornithopod is a pedal phalanx lacking collateral pits and girdling sulcus of most dinosaur toe bones, but has lateral lappet basins like large ornithopod dinosaurs. The age of the Oregon toe bone is between that of well-known Tenontosaurus and Eolambia from Utah and Wyoming. Associated fossil plants in the same marine shales are evidence of a coastal redwood forest like that of modern Redwoods National Park. A further similarity with Northern California today, are the gravelly sediments of shingle beaches and alluvial fans from nearby sea cliffs. A second report in October was a sacrum of an equally large ornithopod from marine sandstone of Cape Sebastian, found along with ammonites and inoceramids dated to about 74 Ma (late Campanian, Late Cretaceous). This specimen was first discovered in 1969 by Don Savage of Berkeley, and collected in 1994 by David Taylor, but preparation from its very hard matrix was completed recently. It has eight co-ossified vertebrae, an undulose iliac bar, and tall strut-like sacral ribs fused centrally to the centra. The most similar known sacra are those of hadrosaurine duckbills of the genus Kritosaurus. Associated fossil leaves are evidence of broadleaf forest flanking shallow marine or shore-face sandstones of a low gradient coastal plain.