Early-Middle Triassic fluvial ecosystems of Mallorca (Balearic Islands): Biotic communities and environmental evolution in the equatorial western peri-Tethys

During the Early-Middle Triassic, the biosphere was recovering from the most severe mass extinction event of multicellular life, in the Permian-Triassic transition. Continental basins corresponding to present-day Mallorca (Balearic Islands, western Mediterranean) were located in the equatorial region of the supercontinent Pangaea, in the western peri-Tethys. Its recorded stratigraphic succession can be divided into four alluvial/fluvial formations, formally described here: Punta Roja Formation, Estellencs Formation, Pedra Alta Formation and Son Serralta Formation. Based on an exhaustive review of all available literature and new stratigraphic and palaeontological data, an upper Olenekian-lower Anisian interval is proposed for the whole succession. The richest fossil assemblage is that of Estellencs Formation, with abundant invertebrate and vertebrate trace fossils, and remains of plants, arthropods and rare fishes, which together represent a lotic/riverine ecosystem with a relatively complex food web. Plants and insects show strong biogeographical affinities with those of the Vosges, in central Europe; clam shrimps are similar to those of central Europe and Asia; and tetrapod tracks are also reminiscent to those of Eurasia and North America. Ultimately, integration of all these data provides a comprehensive and multidisciplinary characterisation of one of the oldest Triassic ecosystems of equatorial Pangaea, providing new insights to understand the evolution of palaeoenvironments of the Iberian Plate, an area that has historically suffered from severe undersampling.