Large well-preserved crocodylomorph tracks from the Lower cretaceous (? Aptian) Jinju formation of South Korea, represent the well-known crocodylomorph ichnogenus Batrachopus. the Korean sample includes multiple, narrow-gauge, pes-only trackways with footprint lengths (FL) 18-24 cm, indicating trackmaker body lengths up to ~3.0 m. Surprisingly, the consistent absence of manus tracks in trackways, with well-preserved digital pad and skin traces, argues for bipedal trackmakers, here assigned to Batrachopus grandis ichnosp. nov. No definitive evidence, either from pes-onmanus overprinting or poor track preservation, suggests the trackways where made by quadrupeds that only appear bipedal. this interpretation helps solve previous confusion over interpretation of enigmatic tracks of bipeds from younger (? Albian) Haman formation sites by showing they are not pterosaurian as previously inferred. Rather, they support the strong consensus that pterosaurs were obligate quadrupeds, not bipeds. Lower Jurassic Batrachopus with foot lengths (FL) in the 2-8 cm range, and cretaceous Crocodylopodus (FL up to ~9.0 cm) known only from Korea and Spain registered narrow gauge trackways indicating semi-terrestrial/terrestrial quadrupedal gaits. Both ichnogenera, from ichnofamily Batrachopodidae, have been attributed to Protosuchus-like semi-terrestrial crocodylomorphs. the occurrence of bipedal B. grandis ichnosp. nov. is evidence of such adaptations in the Korean cretaceous. Crocodylomorph tracks are generally rare in the Mesozoic of Asia. It has been suggested that this is in part due to the lack of sedimentary facies representing suitable habitats for this group of ostensibly aquatic trackmakers 1. However, the crocodylomorph ichnofamily Batrachopodidae 2,3 appears to represent more terrestrially-adapted forms 3,4. As currently defined, the batrachopodids 5 include Batrachopus and Crocodylopodus, the former mostly known from small tracks (~2.0-8.0 cm long) from the Lower Jurassic of North America 4 , Europe 5,6 and Africa 7 , the latter primarily from the Cretaceous of Europe 8,9. The ichnofamily also includes Antipus known only from one well-described Lower Jurassic trackway from North America which is considered a synonym of Batrachopus by some 3 , but not all ichnologists 10. Recently Crocodylopodus was reported from the Lower Cretaceous (?Aptian) 11 Jinju Formation of Korea 12,13 , where it represents the first Asian occurrence, and adds to the extraordinarily rich Jinju Formation, ichnofauna described as a Konservat-Lagerstätten 14-19. Spanish 8,9 and Korean 12,13 Crocodylopodus represent relatively small animals (footprint lengths less than ~9.0-10.0 cm) with slender digit traces, which may reflect penetrative track preservation 20. However, the trackway configuration is diagnostically crocodilian, with elongate tetradactyl pes and outwardly rotated pentadactyl manus, not unlike those of extant crocodilians 21-23 (Supplementary Information: SI Fig. 1). Here we report on a large, newly-discovered Jinju Formation assemblage wi...