Well-preserved theropod tracks from the Upper Cretaceous of Hwasun County, southwestern South Korea, and their paleobiological implications

Abundant dinosaur fossils including footprints, eggs and nests, teeth, and bones have been found from the Cretaceous nonmarine deposits of Korea. Among them, dinosaur tracks are the most distinctive, and some tracksites are among the most famous in the world. Approximately 1500 well-preserved dinosaur footprints, including more than 60 trackways, have been excavated from the Cretaceous Neungju Group in a quarry in Seoyu-ri, Hwasun County, Jeollanam-do, South Korea. Unlike other dinosaur fossil sites in South Korea, most of the tracks found in the area belong to theropods, especially small-sized theropods. The tracks show significant variation in size, morphology, and divarication. On the basis of morphology and size, the theropod tracks have been classified into three types. The first type is characterized by its small size, wide divarication, and slender digits, which can be more closely compared to Magnoavipes. The second type shows slightly thicker digits than the first one and narrow toe impressions and is similar to Ornithomimipus or Xiangxipus. The footprints of the third type belong to large theropods and display distinct sharp claw impressions. The calculated body sizes of the dinosaurs vary between small theropods with an estimated hip height of 68.4–194.5 cm, and large theropods with a maximum estimated hip height of 260.9 cm. The variety of morphotypes and sizes of the footprints and the calculated body sizes indicate that different theropods with various gaits inhabited in the study area during the Cretaceous. On the basis of the speed and gait analyses, it is inferred that the small theropods in the area were trotting, while the large theropods were walking slowly. The fossil site also shows diverse gaits with unusual walking patterns and postures in some tracks.