A high-density Grallator assemblage from the Haman Formation (Cretaceous), Korea: implications for Cretaceous distribution of grallatorids in east Asia

ABSTRACT

Monospecific assemblages of non-avian theropod tracks are relatively rare in the Cretaceous of Korea, where assemblages dominated by the tracks of diverse tetrapods (birds, sauropods, ornithopods, and pterosaurs) are well known and widely distributed in the Haman and Jindong formations (Hayang Group). To date, few high-density assemblages of theropod tracks have been documented. A Haman Formation site on Adu Island reveals a small high-density assemblage of Grallator tracks (~29 tracks/m²). The tracks, which indicate registration on a sandy substrate infused with microbial mat, are indistinguishable from Grallator tracks known from a few other Lower Cretaceous sites in China and east Asia. Early and Middle Jurassic Grallator-dominated assemblages are common in east Asia, and persist into the Late Jurassic- Early Cretaceous (Neocomian) transition in China, where they are typically only associated with sauropodomorph tracks. Post-Neocomian (Aptian-Albian) Cretaceous assemblages from Korea are much more diverse, and characterised by tracks of sauropod and ornithopod dinosaurs, non-avian and avian theropods (birds), pterosaurs and other tetrapods. Post-Neocomian assemblages dominated by theropod tracks, are rare and no large monospecific grallatorid assemblages are currently known.

KEYWORDS:

• Grallator
• Haman Formation
• Korea
• Early Cretaceous

Acknowledgments

We thank Nora Noffke Old Dominion University for her comments on the crinkle structures shown in Figure 6. We also thank Anthony Romilio, University of Queensland, for showing us his 3D images of the Grallator tracks described here from Adu Island site VT-2, which were obtained in 2016. They were useful in demonstrating the shallowness of many of the traces, and we also thank him for his helpful review of an earlier version of this manuscript. Charles Helm, Tumbler Ridge Museum, British Columbia, also provided an equally helpful review. The study was funded by Sacheon City.

Disclosure statement

No potential conflict of interest was reported by the author(s).