The exposure and preservation of dinosaur footprints on intertidal shore platforms

Abstract

Dinosaur footprints are commonly found on intertidal ledges along rocky coasts. Driven by the continual bedrock downwearing, intertidal fossil tracks are considered ephemeral features on the timescales that drive landscape evolution. Therefore, determining their temporal longevity is critical in managing these paleontological features. In this study, we explored two early Cretaceous Ornithopod dinosaur footprints exposed on a shore platform in Otway Ranges Region, south-eastern Australia, which also hosts the world’s longest continual monitoring sites of platform downwearing erosion. The platform morphology and bedrock hardness were surveyed to explore the preservation of fossil tracks under different erosion conditions. With a mean downwearing rate of 0.25 mm/yr, the mould-type track of 5 mm negative relief could have a preservation age of 20 years. However, the longevity could vary from 4 to 6 years up to centuries due to the wide range of erosion rates (0.008–1.8 mm/yr) found in this region. The potential for track preservation was also controlled by rock type, elevation and hardness. The results suggest the erosion of the bedrock is primarily driven by subaerial weathering processes through granular-scale disintegration. Influenced by the varying efficacy of subaerial weathering, fossil track located at higher, inland sections tends to have faster erosion and shorter longevity while located at lower, seaward areas tends to have lower erosion rates and therefore higher longevity. Immediate conservation measures should be conducted to protect tracks of low relief (1–2 mm) or located in the fast-eroding zone which have correspondingly short longevity.