First footprints occurrence from the Muschelkalk detritical unit of the Catalan Basin: 3D analyses and palaeoichnological implications

Abstract

Fossil vertebrate footprints are known from several Triassic localities of the Iberian Peninsula. Geological setting and palaeoichnological analyses are presented from the first recovered tetrapod footprints from the Middle Muschelkalk facies of the Iberian Peninsula. The studied outcrop is 40 km NW from Barcelona, in the Catalan Coastal Ranges (Catalan Basin, NE Iberian Peninsula). The stratigraphic section is ascribed to Middle Muschelkalk facies from Late Anisian-Early Ladinian age (Middle Triassic), and comprises mainly red mudstones with interbedded sandstones. Tetrapod footprints are located at the upper part of decametric medium-grain size sandstone intercalated in metric-submetric mudstone beds sequence. The general palaeoenvironment is a floodplain with episodic torrential events. Several 3D models from footprints were made by photogrammetry technique, being useful in the morphological description and depth analyses as indicator of the trackmaker’s pressure weight distribution and locomotion-substrate interaction. Tetrapod footprints are preserved in convex hyporelief in a sandstone bed with ripple laminations, mud-cracks and invertebrate traces. Substrate under the sand was muddy and soft, with progressive desiccation. There are eight footprints from different specimens and trackmakers. Seven of them are attributed to Isochirotherium isp. And Chirotherium isp. In special, three of them clearly resemble to pentadactyl morphology of chirotheriid pes. Potential trackmakers are crurotarsians. The last footprint is isolated and is referable to Rhynchosauroides isp. Potential trackmakers is a lacertoid-type reptile. The finding partially confirms the presence of homogeneous fauna diversity in the Middle Triassic of Europe Dominated by the same ichnofamilies reported here