First Report of Small Ornithopodichnus Trackways from the Lower Cretaceous of Sichuan, China

Abstract

Trackways of ornithopods are well-known from the Lower Cretaceous of East Asia, particularly in Korea and China. However, most morphotypes have been identified as Caririchnium which is characterized by moderate mesaxony, the ratio length = width, or length > width and, in some cases, by a quadrupedal gait. In 2009 the ichnogenus Ornithopodichnus, which exhibits distinctively weak mesaxony and a broader, transverse pes imprint with the ratio length < width, was identified in Korea, on the basis of material with suboptimal preservation. The trackmaker was a large ornithopod. Subsequently, in 2009 a second report recognized Ornithopodichnus in China, the trackmaker being a moderately large quadruped. In 2012, Ornithopodichnus was described on the basis of well-preserved material from the Upper Cretaceous of Korea, in this case left by a small, gregarious biped. Herein we document, a fourth occurrence of Ornithopodichnus in the Lower Cretaceous Feitianshan Formation of Sichuan, China which is a further example of trackways that can be attributed to small, bipedal and gregarious ornithopods. Morphology, size, trackway pattern and speed of locomotion correspond well with trackways known from the Korean Hwasun tracksite. Possibly, the occurrence of Ornithopodichnus which is restricted to East Asia thus far, is related to ecological and biogeographical pecularities in this area.