Trackway evidence for large bipedal crocodylomorphs from the Cretaceous of Korea

Abstract

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...

New dinosaur, crocodylomorph and swim tracks from the Late Jurassic of the Lusitanian Basin: implications for ichnodiversity

“…In addition, Mateus et al (2017) described Angolaichnus adamanticus from the Early Cretaceous of Angola. ICNO.62 differs from Batrachopus (Olsen & Padian 1986; Lockley & Meyer 2004; Kim et al 2020) in the digit proportions, the orientation of the digits and especially in the digital divarication (higher in ICNO.62). With respect to Hatcherichnus sanjuanensis from the Late Jurassic of the United States (Foster & Lockley 1997), ICNO.62 differs in the length of the digits, since digit III is the longest in Hatcherichnus sanjuanensis whereas in ICNO.62 it is digit II (although DII is almost subequal to DIII), but especially in that digits I and II are not recurved laterally and the total divarication is higher in ICNO.62.…”

“…Specimen ICNO.62 has been interpreted as a left pes of a crocodylomorph. During the Mesozoic, three main crocodylomorph ichnotaxa have been described: Batrachopus (Early Jurassic‐Cretaceous), Hatcherichnus (Late Jurassic‐Cretaceous) and Crocodylopodus (Late Jurassic‐Cretaceous) (Lockley & Meyer 2004; Lockley et al 2020; Kim et al 2020 and references therein). In addition, Mateus et al (2017) described Angolaichnus adamanticus from the Early Cretaceous of Angola.…”

A new pterosaur tracksite from the Lower Cretaceous of Wuerho, Junggar Basin, China: inferring the first putative pterosaur trackmaker

“…There is another fossil of H. gainensis from the Lower Cretaceous (Haman Formation) that was considered to be pterosaur footprints (Fig. 5F) (Kim et al, 2012), but more recent studies attributed it to bipedal crocodylomorph tracks (Kim et al, 2020).…”

A diverse Late Cretaceous vertebrate tracksite from the Winton Formation of Queensland, Australia

“…Whereas the Triassic record of crocodylomorph tracks is restricted to North America and Europe (Klein & Lucas, 2010), the Jurassic crocodyliform track record is more extensive (Lockley & Meyer, 2004), spanning North America (Foster & Lockley, 1997;Lockley & Foster, 2010;Lockley, Kirkland & Milner, 2004;Lockley et al, 2018b), Europe (Avanzini et al, 2007;Castanera et al, 2021;Moreau et al, 2019;Romano & Whyte, 2010), Asia (Lockley et al, 2010b), Iran (Abbassi et al, 2015), and Africa (Klein et al, 2018;Olsen & Galton, 1984). The Early Cretaceous crocodyliform track record is similarly extensive, with records from North America (Houck et al, 2010;Kukihara & Lockley, 2012;Kukihara, Lockley & Houck, 2010;Lockley, 2010;Lockley, Kukihara & Mitchell, 2006;Lockley et al, 2010a;Lockley et al, 2014;McCrea et al, 2014), Europe Pascual Arribas et al, 2005), Asia (Kim et al, 2020;Le Loeuff et al, 2010;Lockley et al, 2010b;Lockley et al, 2020), and Brazil (Campos, Da Silva & Milàn, 2010). By contrast, the Late Cretaceous crocodyliform track record is relatively limited, the only reports being from North America (Falkingham, Milàn & Manning, 2010;Lockley et al, 2018a;, 2014; Simpson et al, 2010), Europe (Segura et al, 2016;Vila et al, 2015), and Asia (Lee et al...…”