A Paradise of Mesozoic Birds: The World's Richest and Most Diverse Cretaceous Bird Track Assemblage from the Early Cretaceous Haman Formation of the Gajin Tracksite, Jinju, Korea

Abstract

More than 2,500 well-preserved bird tracks associated with theropod and sauropod tracks are recorded from a dense assemblage in lacustrine deposits of the Early Cretaceous Haman Formation of the Gajin area, Jinju, Korea. These tracks are preserved in the recently constructed Fossil Heritage Hall at the Gyeongsangnamdo Institute of Science Education. Bird tracks are attributed to Ignotornis gajinensis ichnosp. nov., Koreanaornis hamanensis, Goseongornipes markjonesi, and ?Aquatilavipes. Like G. markjonesi, I. gajinensis is a semi-palmate bird track, similar to Hwangsanipes (ichnofamily Ignotornidae) with a postero medially directed hallux and characterized by interdigital angles between digits II and III larger than III and IV. However, Hwangsanipes is a larger morphotype than Ignotornis with a more pronounced semipalmate web. I. gajinensis has associated arcuate to semi-circular, double-grooved, or paired impressions resulting from spoonbill-like feeding behavior. Similar rare but more linear traces occur in one Ignotornis specimen from the Cretaceous of Colorado. The Gajin site represents a record of the world's most-dense assemblage of bird tracks (up to ∼600 per m2) at a single locality and provides striking evidence of the diversity of avian ichnotaxa during the Cretaceous. The Gajin tracksite provides new insight into the morphology of four of the eight ichnogenera known from the Cretaceous of Korea. The Goseongornipes sample is the largest and best-preserved available. In the case of Ignotornis, feeding traces shed new light on behavior and paleoecology of the trackmakers, which appear to have been remarkably convergent with modern shore birds.