Carbon isotope (δ13C) differences between Late Cretaceous ammonites and benthic mollusks from Antarctica

Abstract

Abstract Ammonites are one of the most common fossils of the Mesozoic, but there is little consensus on their mode of life. Isotopic studies have been used to reconstruct their preferred water temperature from δ 18 O measurements, but δ 13 C values have more ambiguous interpretations. Previous studies have recorded population differences in δ 13 C values between ammonite and benthic organisms without explaining the cause in detail. Here we examine a molluscan community from Seymour Island, Antarctica and find a 4‰ carbon isotope offset between ammonites and other benthic mollusks. The most likely cause of this anomaly is an increased metabolic carbon contribution to ammonite shell material when compared with other mollusks, but we cannot rule out the possibility of a methane seep contribution. Increased respired CO 2 production could be generated by a more active lifestyle and increased energy demands, which may have increased the susceptibility of ammonites to the end Cretaceous mass extinction.