ICHNOLOGICAL INSIGHTS ON HABITAT PREFERENCES WITHIN HIGH-LATITUDE HADROSAURS (CRETACEOUS CHIGNIK FORMATION, ANIAKCHAK NATIONAL MONUMENT, SOUTHWESTERN ALASKA)

The Cretaceous Chignik Formation of Aniakchak National Monument (Alaska Peninsula) contains an abundance of dinosaur footprints. Paleomagnetic analyses show these rocks were deposited at approximately 57˚ N, placing this rock unit within the ancient sub-Arctic. Detailed sedimentological work on the upper 300 m of section indicates that the entire section represents a tidally influenced estuary-fill. Marine shoreface deposits are incised by a thick sandstone package interpreted as a multi-story, meandering fluvial channel valley-fill. This is overlain by outer estuary deposits, containing two thick red paleosols, culminating in estuary mouth sands with disarticulated bivalve shells. This succession is overlain by an inner estuarine succession containing weakly developed paleosols, tidal channels, tidal flats, and thin coals, overlain by a tidally-influenced alluvial succession containing small meandering fluvial channels, floodplain successions, and thin, grey and red paleosols.

Most dinosaur tracks can be attributed to hadrosaurs. Other tracks can be attributed to armored dinosaurs, meat-eating dinosaurs, and two kinds of fossil birds. Hadrosaur tracks range from those made by full-grown adults to juveniles. With over 100 hadrosaur tracksites now recorded the tracks are contained primarily within three broad stratigraphic intervals and record differing population profiles. More dynamic sedimentary environments contain adult footprints while more stable sedimentary environments have a broader range of sizes of hadrosaur tracks that includes juveniles. Based on the repeated occurrences of standing forest horizons and well- developed paleosols within the stable depositional settings, we infer that there was more vegetative protection which is why juvenile hadrosaurs preferred these environments. This work demonstrates habitat preference within different age classes of these ancient high-latitude dinosaurs.