Multiproxy reconstruction of the palaeoclimate and palaeoenvironment of the Middle Miocene Somosaguas site (Madrid, Spain) using herbivore dental enamel

Abstract

Profound palaeoclimatic changes took place during the Middle Miocene. The Miocene Climatic Optimum (~ 20 to 14–13.5 Ma) was followed by a sudden (~ 200 ka) decrease in temperature and an increase in aridity around the world as a consequence of the reestablishment of the ice cap in Antarctica. Somosaguas palaeontological site (Madrid Basin, Spain) has provided a rich record of mammal remains coincident with this global event (Middle Miocene Biozone E, 14.1–13.8 Ma). It contains four fossiliferous levels (T1, T3-1, T3-2 and T3-3, with T1 being the oldest) that span an estimated time of ~105–125 ka. Scanning Electron Microscope (SEM) and Rare Earth Element (REE) analyses performed on herbivore tooth enamel (Gomphotherium angustidens, Anchitherium cf. A. cursor, Conohyus simorrensis, Prosantorhinus douvillei and ruminants) indicate that diagenetic processes have not been intense enough as to obscure the original geochemical signal. Stable isotope (δ18OCO3, δ13CCO3 and δ18OPO4) analyses have been measured on the herbivore tooth enamel across these levels with the aim of determining to what extent the global cooling and aridity pattern is recorded at this site. A decrease in δ18OCO3 and δ18OPO4 has been detected from T1 to T3-3 and T3-1 to T3-3 respectively indicating a progressive drop of about 6 °C (from around 18 °C to 12 °C) in mean annual temperatures within T3. Tooth enamel δ13C values experience an increase from T3-1 to T3-3 suggesting an increase in aridity. Ba/Ca analyses have also been performed on the tooth enamel in order to detect changes in the palaeoecology of the studied taxa. This ratio allows the establishment of particular feeding patterns such as a more browsing habit in the case of Gomphotherium angustidens compared to Anchitherium cf. A. cursor as suggested by higher Ba/Ca values in the latter. Trace elements do not support any significant change across the succession in the dietary behaviour of the species analyzed, despite the stable isotopes evidence of an important palaeoclimatic shift from T1 to T3-3.