Oxygen stable isotopes analyses as a tool for palaeoecological reconstruction: an example from a Late Jurassic fish fauna (Kimmeridgian, Swiss Jura)

LÉA LEUZINGER; LASZLO KOCSIS; JEAN-PAUL BILLON-BRUYAT; SILVIA SPEZZAFERRI; TORSTEN VENNEMANN

Diamante

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados,; 2015

The proportion of the different oxygen stable isotopes present in water is linked to several environmental parameters such as evaporation rate, salinity and temperature. Vertebrates living in aquatic environment use the oxygen of the ambient water to mineralize hard tissues of bones and teeth, recording thereby measurable information on its isotopic composition. Enamel of fish teeth is an ideal material for oxygen isotope analyses because it is highly resistant to alteration (fluorapatite) and precipitates in isotopic equilibrium with the surrounding water, making it a powerful palaeoenvironmental proxy. Using a case study of a Kimmeridgian chondrichthyan fauna from the Porrentruy area (Ajoie region, Swiss Jura), we present the usefulness of oxygen isotopic analyses in the field of vertebrate palaeontology, and the ecological and environmental interpretation that can result. The oxygen isotopic composition of chondrichthyan teeth was measured and compared to that of osteichthyan teeth and turtle bone. The results reveal a so far unique euryhaline isotopic signature for the hybodont (primitive) shark Asteracanthus, associated with marine deposits, and consequently support the presence of freshwater near the shallow-water carbonate platform of this region, as already inferred by the record of wood remains and numerous dinosaur footprints. At European scale, this freshwater-influenced isotopic signal provides further information on the ecological repartition of modern and primitive sharks at a key moment of their evolution history, when hybodonts are little by little restricted to reduced salinity environments.