Abstract

Dinosaur track beds occur at several localities in the uppermost Cretaceous (Maastrichtian) North Horn Formation in the Wasatch Plateau, central Utah. The track bed localities, separated by up to 80 km, also contain dinosaur body fossils. At the type locality at North Horn Mountain in Emery County, more than 100 individual exposures and/or stratigraphic levels within a 1.2-km2 study area exhibit tracks in vertical cross-sectional view. These biogenic structures are similar to others that have been interpreted elsewhere as deep dinosaur tracks. At the type section, track beds vertically span at least 183 m from the base of the formation up to a few meters below the highest dinosaur eggshells, which are interpreted to occur immediately below the Cretaceous-Tertiary (K-T) boundary interval. Track occurrence in the North Horn Formation demonstrates that large dinosaurs were present in central Utah until very shortly before the K-T boundary.

The track structures feature deformation, overprinting, and slip striae that are interpreted to exhibit individual dinosaur behavior. Some striae exhibit repeating patterns that suggest tubercle configuration or scale patterns on dinosaur feet. Track groupings at any individual level suggest that many animals repeatedly congregated in topographic lows of the floodplain or near shifting anastomosing river systems, and track-size distribution largely suggests the presence of different sizes or age groups of herbivores. The conditions produced by anastomosed fluvial environments provided the depositional setting responsible for formation and preservation of most of the North Horn tracks.

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