DINOSAUR ICHNOLOGY AND PALEOENVIRONMENTS FROM THE CHIGNIK FORMATION (ANIAKCHAK NATIONAL MONUMENT, LATE CRETACEOUS, SOUTHWESTERN ALASKA)

While there are now numerous records of dinosaurs from Cretaceous rocks around the state of Alaska, very few fossil records of terrestrial vertebrates are known from the Mesozoic rocks of the southwestern part of the state. Here we report the new discovery of extensive occurrences of dinosaur tracks from exposures of the Cretaceous Chignik Formation in Aniakchak National Monument of the Alaska Penninsula. These tracks are in the Late Cretaceous (Maastrichtian) Chignik Formation, a cyclic sequence of rocks, approximately 500 – 600 m thick, representing shallow marine to nearshore marine environments in the lower part and continental alluvial coastal plain environments in the upper part of the section. These rocks are part of the Peninsular Terrane and paleomagnetic reconstructions based on the volcanic rocks of this terrane suggest that the Chignik Formation was deposited at approximately its current latitude which is almost 57 degrees N.

Recent work in Aniakchak National Monument through the last three field seasons has revealed over 50 new track sites, dramatically increasing the dinosaur record from the Alaska Penninsula. Though the vertebrate ichnofauna now includes tracks attributable to fishes, small and large birds, large theropods, and ankylosaurs, the track assemblage from this part of the Chignik Formation, approximately 90 % of all tracks represent hadrosaurian dinosaurs. The hadrosaur tracks range in size from those made by full-grown adults to juveniles.

Previous interdisciplinary sedimentologic and paleontologic work in the correlative and well-known dinosaur bonebeds of the Prince Creek Formation 1400km-1500km further north in Alaska suggested that high-latitude hadrosaurs preferred distal coastal plain or lower delta plain habitats. The current interdisciplinary paleontologic and sedimentologic project in the Chignik Formation finds that hadrosaur tracks here were also made in distal coastal and delta plain conditions. This similarity may corroborate the habitat preference model for Cretaceous high-latitude dinosaurs proposed for the data gathered from the Prince Creek Formation.