First New Zealand record of probable dinosaur footprints from the Late Cretaceous North Cape Formation, northwest Nelson

Abstract

Structures that are interpreted as dinosaur footprints are recorded from six localities within the Late Cretaceous (Maastrictian) aged North Cape Formation of northwest Nelson. These are the first dinosaur footprints to be recognised from New Zealand and the first occurrence of dinosaurs from the South Island, and add considerably to our knowledge of New Zealand dinosaurs, which currently is based on only three dinosaur bone fossil localities. The trace fossils occur within sandstone beds that form part of a succession of intertidal sandstones and mudstones. In cross-section, the footprints form structures with sharp vertical margins, infilled with both massive or laminated sandstone and discrete blocks of sandstone and mudstone. Sediments underlying are either planar with the base of the structures or deformed downward, and overlying sediments drape into the tops of the structures. In plan view, structures are usually roughly circular, with clear margins, and are filled with both blocky and massive sandstone, as well as sandstone with arcuate laminae or low-angle shear planes. One structure is more elongate and appears to represent the left foot impression of a dinosaur.The possibility that these structures were formed by physical or sedimentological processes is ruled out. Based on morphology, it is most likely these structures represent sauropod footprints. Sauropods were large dinosaurs with pentadactyl (5-toed) feet that, based on studies outside New Zealand, produced no clear toe impressions, but rather had a broad club-like footprint. Such a foot would have provided support for these large animals in coastal plain to intertidal settings, dominated by soft sand and mud or waterlogged swampy environments. Based on the age of the formation and knowledge of the evolution of the sauropods, it is further concluded that these structures may represent footprints of the sauropod superfamily Titanosaurida, though it is not possible to characterise them taxonomically any further.