Gregarious behaviour among non-avian theropods inferred from trackways: A case study from the Cretaceous (Cenomanian) Candeleros Formation of Patagonia, Argentina

HEREDIA, A.M.; DIAZ MARTINEZ IGNACIO; PAZOS P.J.; COMERIO M.; FERNÁNDEZ, DIANA E.

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019

0031-0182

Gregarious behaviour among dinosaurs has been inferred from several lines of evidence (monospecificbonebeds, skeletal morphology, phylogenetic inferences, comparison with modern ecosystems andparallel trackways with particular characteristics), but is relatively poorly documented for non-aviantheropods. Here, we report five parallel theropod trackways of large track size (average length of 28cm) in the Cretaceous (Cenomanian) Candeleros Formation from northwestern Patagonia, Argentina.The tracks are provisionally assigned to aff. Asianopodus pulvinicalx and considering the autopodmorphology of the theropod taxa documented in the Candeleros Formation, abelisaurid theropods aresuggested as trackmakers. The trackways possess similar stride, speed estimation, direction andpreservational features, and track show uniform depth and do not overlap. Physical barriers (i.e., largefluvial channels or perennial lake) that could influence the direction of the theropod trackmaker gaitswere not recognised in the section. Taking into account these considerations, a gregarious behaviourfor the abelisaurid theropod trackmakers is proposed. The tracks are preserved as shallow undertracksin a medium-grained sandstone bed deposited in a floodplain setting. The tracking surface isinterpreted as the overlaying layer of muddy-siltstone. The occurrence of swelling clays and microbialmats in the track-bearing level could have contributed to the substrate stabilisation and their role in thepreservation is discussed.