Glaucoceras gen. nov., a small uncoiled ammonoid from the Tethyan late Hauterivian (Early Cretaceous): evolutionary implications at the dawn of the diversification of heteromorphic lineages

Abstract

The poorly-known species Baculites Renevieri Ooster, 1860 is revised using the type material from Switzerland and new conspecific specimens collected in deposits from Mallorca and the Betic Cordillera (Western Mediterranean), listing all the previous mentions of the species. The uniqueness of its ornamentation pattern and shell shape compared to other coeval ammonoid faunas demands for the description of Glaucoceras gen. nov. to contain this species. In addition, a thorough comparison of Glaucoceras renevieri to other morphologically reminiscent genera or species is provided. This new set of data allows to improve the knowledge of one of the many phylogenetic lines of heteromorphic ammonites that diversified over the latest Hauterivian in the Mediterranean Province, also providing hints about the timing of those radiation events. This aspect is preliminary explored using data on other coeval heteromorphic ammonoid groups from the literature and new finds, concluding that there occurred two main radiation events of heteromorphic ammonites at the latest Hauterivian, most likely related to environmentally stressful episodes, specifically, transgressive events.