Diminutive pterosaur tracks and trackways (Pteraichnus gracilis ichnosp. nov.) from the Lower Cretaceous Jinju Formation, Gyeongsang Basin, Korea

Abstract

Small pterosaur tracks were discovered from the Cretaceous Jinju Formation of Jinju City, South Korea, now famous as an ichnological Konservat-Lagerstätte and source of large numbers of well-preserved tetrapod track assemblages. These small tracks are among ∼2500 reported from the vicinity of the Jinju Pterosaur Tracks Museum which represented the world's largest concentration of pterosaur tracks and multiple pterosaur track-bearing strata. The small tracks, which are the focus of this study are preserved as natural impressions (concave epirelief) on the surface of a dark grey shale slab. Manus tracks have average values of 27.2 mm length, 9.3 mm width and 3.0 length/width ratio. Pes tracks have average values of 27.8 mm length, 12.3 mm width and 2.2 length/width ratio. The sizes of the tracks are about as small as other small pterosaur tracks previously reported from Korea (P. koreanensis), Japan (P. nipponensis) and Spain (P. longipodus and P. parvus). Nevertheless, morphological characteristics of these tracks are clearly distinguished from those of ichnospecies mentioned above in divarication angles between manus digits, shape of pes imprints and length/width ratio of manus. Especially, the high elongation obtained from the narrow width of the manus and the length of elongated digit Ⅲ and the shape of isosceles triangular pes are the most prominent and diagnostic features. Thus, the small pterosaur tracks described herein, Pteraichnus gracilis ichnosp. nov., are considered a different type among established pterosaurian ichnotaxa.