Elusive Cretaceous Gondwanan theropods: The footprint evidence from central Argentina

Abstract

New findings of well-preserved theropod dinosaur footprints from the Albian Lagarcito Formation (Sierras de Las Quijadas National Park, San Luis, Argentina) are described and its paleoenvironmental and stratigraphic context is discussed. The local succession of the formation is represented by three shallowing-upward cycles that were deposited in a lacustrine setting. The theropod footprints occur in sheet flood facies fringing the lake and probably were mostly oriented parallel to the shoreline. The footprints are assigned to Picunichnus quijadaensis Melchor nov. isp. which is distinguished from similar ichnotaxa by the degree of mesaxony, footprint elongation, digit proportions and occasional presence of a hallux impression. Based on the comparison of type material of theropod ichnotaxa, it is suggested that Picunichnus belongs to the ichnofamily Grallatoridae Lull, 1904, which is amended to include Grallator, Anchisauripus, and Prototrisauropus. This revision also suggests the potential recognition of additional ichnofamilies for theropod dinosaur footprints. Preservation of digital pads in P. quijadaensis also permits an osteological comparison with theropods from Gondwana. This comparison is based on the length of pedal bones inferred from P. quijadaensis and similar information on selected Jurassic?Cretaceous theropods. In addition, relative size, age and geographic provenance are also contrasted. There is no known Gondwanan theropod dinosaur with preserved pedal bones that match all these features. The best candidates are the smaller basal coelurosaur Aniksosaurus darwini from the Cenomanian of Patagonia and the similar-sized abelisaurid Majungasaurus crenatissimus from the Maastrichtian of Madagascar. This finding is relevant because the footprints come from a geographic area lacking skeletal or other footprint records of Cretaceous theropods and because the producer is apparently not recorded by skeletal remains in Gondwana continents.