Unusual Didactyl Traces from the Jinju Formation (Early Cretaceous, South Korea) Indicate a New Ichnospecies of Dromaeosauripus

Abstract

New didactyl dinosaur tracks from the fine-grained sandstone of the Early Cretaceous Jinju Formation, Namhae area, Korea, are herein described as Dromaeosauripus jinjuensis ichnosp. nov. A trackway about 4.3 m long is composed of 12 consecutive didactyl traces. The tracks average about 9.3 cm long and 6.8 cm wide. Pace, stride, and pace angulation are 40 cm, 80 cm, and 175°, respectively. D. jinjuensis is a small didactyl track characterized by slender digit impressions, very narrow divarication angle between digits III and IV, digit III slightly longer than IV, and sharp claw impressions. D. jinjuensis measurements differ significantly from D. hamanensis in length (only 60% of the latter), width (81%), length/width ratio (0.72), and digit thickness (55%). The didactyl tracks are tentatively interpreted to be formed by a small dromaeosaurid walking bipedally on a lake margin. D. jinjuensis represents the oldest theropod dinosaur tracks described in the Cretaceous of Korea and the second ichnospecies of Dromaeosauripus. It suggests more diversity and wider stratigraphic and paleogeographic distribution of dromaeosaurids. The track morphology may also indicate a more digitigrade gait.

Keywords:

• Didactyl tracks
• Dromaeosauripus
• Cretaceous
• Jinju Formation
• Korea

ACKNOWLEDGMENTS

This research was financially supported by a grant (J. Y. Kim, 2010-0023409) from the National Research Foundation of Korea. The authors thank M. S. Oh for help in the laboratory. We also thank Spencer Lucas and Justin Spielmann, both of the New Mexico Museum of Natural History and Science, for their helpful reviews.