Middle Triassic sharks from the Catalan Coastal ranges (NE Spain) and faunal colonization patterns during the westward transgression of Tethys

Abstract

Palaeogeographic changes that occurred during the Middle Triassic in the westernmost Tethyan domain were governed by a westward marine transgression of the Tethys Ocean. The transgression flooded wide areas of the eastern part of Iberia, forming new epicontinental shallow-marine environments, which were subsequently colonized by diverse faunas, including chondrichthyans. The transgression is recorded by two successive transgressive–regressive cycles: (1) middle–late Anisian and (2) late Anisian–early Carnian. Here, we describe the chondrichthyan fauna recovered from several Middle Triassic stratigraphic sections (Pelsonian-Longobardian) located at the Catalan Coastal Basin (western-most Tethys). The assemblage consists of isolated teeth of the species Hybodus plicatilis, Omanoselache bucheri, O. contrarius and Pseudodalatias henarejensis. Our data complement a series of recent studies on chondrichthyan faunas from Middle-Late Triassic marine basins of the Iberian Peninsula, allowing us to evaluate patterns of faunal colonization. Sharks that reached East Iberia during the first transgressive pulse (Anisian) show strong affinities with the Sephardic bioprovince (related with the Neotethys Ocean) whereas a later increase in chondrichthyan diversity (during the Ladinian transgressive pulse) is due to the arrival of taxa with affinities to European faunas (Palaeotethys). This contrasts with recently evaluated colonization patterns of invertebrates and conodonts, where Middle–Upper Anisian assemblages are composed of taxa with affinities to the Alpine/Germanic bioprovince whereas faunas from the Sephardic bioprovince only reached the shallow waters of the Iberian peninsula during the second (Ladinian) transgressive pulse. The differences between chondrichthyans vs. invertebrate and conodonts colonization patterns are explained here on the basis of differing dispersal strategies. Our finding suggests the existence, during the Anisian, of connections between Palaeo- and NeoTethys through the western Cimmerian microcontinent, which served as pathways for the entrance of chondrichthyans from the Sephardic bioprovince.