Ornithopodichnus and Pes-Only Sauropod Trackways from the Hwasun Tracksite, Cretaceous of Korea

Abstract

Trackways of small (foot length ∼12–15 cm) robust ornithopods are relatively uncommon in the Cretaceous, where most tracks attributed to iguanodontids and hadrosaurs range in size from ∼20–80 cm. The Hwasun site, previously noted for its abundant theropod trackways, also reveals one horizon (L2) with at least six parallel trackways of small blunt-toed ornithopods with wide tracks, short steps and typical inward rotation of the pes. The site also reveals a second horizon (L4) which yields a single clear trackway of a much larger blunt-toed ornithopod. Although allometric trends in tridactyl track assemblages tend to show increased trackway width and reduced anterior projection of digit III (reduced mesaxonic emphasis) with increasing size, the small Hwasun ornithopods reveal unusually wide tracks with reduced mesaxony. The tracks are herein assigned to the ichnogenus Ornithopodichnus. A map of previously unmapped Level 4 is presented showing the context of the large ornithopod tracks on the same surface as an unusual pes-only trackway with distinctive claw traces and sediment rims. This surface also reveals isolated sauropod manus tracks and various underprints.