First evidence of rooting lycopsids preserved as imprints and trace fossils from the Silves Sandstone (Upper Triassic, eastern Algarve, South Portugal)

Abstract

Rooting lycopsids, preserved as imprints on the Upper Triassic Silves Sandstone in the Eastern Algarve region (South Portugal), are recorded for the first time in this area. The Silves Sandstone is composed of the characteristic dark red sandstone and conglomerates of this formation and contains all the studied imprints. These have a quadrate or pseudohexagonal outline corresponding to the departure of roots placed in four to six roughly symmetrical points around the stem bases. Two generations of plants are observed, including the imprints of seedings. Palaeoenvironmental conditions for the lower unit have been interpreted as a shallow lagoon or stationary bodies of water in a swap-like environment subjected to sporadic current activity. This would have uprooted stems and ripped off the leaves. The upper unit would correspond to a fluvial environment with the establishment of an inundated floodplain with periodic subaerial exposure; this is where root imprints, shallow vertebrate (Rhynchosauroides isp.) and invertebrate trace fossils (Cochlichnus anguineus, Vagorinchus cf. anyao, Palaeophycus tubularis, Taenidium isp., Scoicia isp.), tetrapod footprints and raindrop imprints were recorded. Lycopsids maw have colonized these marshy areas in between wet (occasional flash floods) and drier episodes. Uprooting of the stems was probably caused by sudden and strong mass flow produced during intervals of heavy rain