Short note on the Sirenia disappearance from the Euro-North African realm during the Cenozoic: a link between climate and Supernovae?

Sirenia are marine mammals that colonized the European shores up to 2.7 Ma. Their biodiversity evolution follows the climate evolution of the Cenozoic. However, several climate events, as well as the global climate trend of this Era are still struggling to be understood. When considering only Earth processes, the climate evolution of the Cenozoic is hard to understand. If the galactic environment is taken into account, some of these climate events, as well as the global climate trend, became more easily understood. The Milky Way, through Supernovae, may bring some answers to why Cenozoic climate had this evolution. With the assumption that SN can induced changes in Earth climate in long time scales, Sirenia disappearance from Europe would be a side effect of this process. Introduction Sirenia, an Order (Sirenia Illiger, 1811) of placental mammals that, along with cetaceans, represent the only mammals that evolved for a fully aquatic life (Clementz et al., 2009), and have the particularity of being the only herbivorous marine mammals (Domning, 2002), commonly named Seacow. They feed mainly on seagrass, although there are some differences between the two extant families, the trichechids and the dugongids. The Trichechidae family is not highly specialized when it comes to food and habitat. They live in fresh and seawater , feeding on more than 60 species of marine plants, and can be considered, as suggested by Anderson (2002), opportunistic feeders on seagrass. The Dugongidae family is more specialized, feeding mainly on seagrass and is almost exclusively found in salt water. These characteristics are not exclusive of the four actual species, as shown by MacFadden et al. (2004), and can be traced back to the extinct species of both families., showing that the Tethys Sea was colonized by these marine mammals in both its north and south margins. Sirenians were abundant in Tethyan coastal waters, and also in the Paratethys and the Mediterranean, which evolved from it. The Sirenia that inhabited the European/North African shores are almost exclusively of the Dugongidae family (more than 95% of the European and North African fossil record belong to dugongids), meaning that they fed mainly on seagrass. Seagrasses are marine phanerogams that colonized the coastal waters around 100 Ma ago (Hemminga and Duarte, 2000). They show few changes in their evolutionary process and many of the genera found today can be traced back to the Eocene (like Cymodocea nodosa and Posidonia sp. from the …