A juvenile ornithopod tracksite from the Lower Cretaceous Haman Formation, South Korea

A new dinosaur tracksite with footprints of non-adult ornithopods was discovered from the Lower Cretaceous Haman Formation (Albian), Gunbuk District, Haman County, South Gyeongsang Province of South Korea in 2018. The tracksite consists of 58 ornithopod footprints (seven short trackways and 26 isolated footprints) within three track-bearing horizons partially exposed on the small creek bottom. Lithofacies and sedimentary structures of the track-bearing horizons and overlying strata suggest a marginal lacustrine environment. All tracks are sub-symmetrical tridactyl and small-to medium-sized pes prints. They have wide, blunt, short digital impressions with a large, rounded heel pad impression. No manus print is observable in the tracksite. Tracks are generally longer than their width with a distinctly developed digit III. Trackways show the inward (negative) rotation of footprints. The morphological characteristics of the footprints are most likely attributable to ichnogenus Caririchnium. A relatively small pes size (lengths range from 13 to 27 cm) indicates that the trackmakers were juvenile to subadult ornithopods when compared with the contemporary large ornithopods in South Korea. The majority of the trackways show preferred orientations with trends of parallel to subparallel groupings on each surface, suggesting gregarious behavior. Notably, the tracksite consists exclusively of juvenile ornithopod dinosaurs, which is an uncommon phenomenon when compared to other ornithopod tracksites with age-mixed or large ornithopod footprints reported from other localities around the world. The absence of the adult ornithopod tracks may be interpreted as the spatial segregation of an ornith-opod population based on their ages and the formation of juvenile-only communities without parental care. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

A new dinosaur tracksite containing footprints of non-adult ornithopods was discovered in South Korea in 2018. The footprints suggest gregarious behavior and the absence of adult tracks, indicating a potential spatial segregation of age groups in ornithopod populations.