Reviving Kalosauropus, an Early Jurassic sauropodomorph track from southern Africa (Lesotho)

Abstract

ABSTRACT Kalosauropus, the ‘beautiful reptile track’, was collected from the Sinemurian–Pliensbachian lower Clarens Formation (upper Stormberg Group) in Lesotho in the 1950s. It was formally described in 2003 when it was transferred to Otozoum, an ichnogenus known in North America, Europe and Africa, and associated with basal sauropodomorphs. This transfer has been questioned due to the significant morphological differences between these two tracks, leaving Kalosauropus in taxonomical limbo. Using digital imaging techniques, herein we demonstrate that diagnostic and quantifiable morphological differences between Kalosauropus and Otozoum justify their separation as two independent ichnogenera. The size-range of Kalosauropus reported from a single site indicates that the bipedal trackmakers were likely juveniles or small-bodied animals. The co-occurrence of morphologically similar but different sized tracks suggests social behaviour among these Early Jurassic trackmakers. Using osteological evidence and foot bone measurements, we also show that Kalosauropus may be attributed to a bipedal massospondylid, representing the iconic and common basal sauropodomorph family from the Early Jurassic of southern Africa. Reinstating Kalosauropus thus not only expands the Early Jurassic sauropodomorph footprint record in southern Gondwana, but also provides a more nuanced understanding of the ichnotaxonomic complexities surrounding the early dinosaurian track record that spans the Triassic-Jurassic boundary globally.