Direct U-Pb Dating of Biogenic Apatite From Vertebrate Fossils

Abstract

The geologic context that fossils provide can be invaluable for understanding the history of a given stratigraphic sequence. Simply understanding the mode of life of a fossil organism can clarify which kind of environment that organism lived in, but a wealth of geochemical information can also be extracted from fossils. Here we present a new technique via advances in ICP-MS technology to directly date a multitude of vertebrate fossil materials, including biogenic apatite from several dinosaurs. Using U-Pb isochrons we are able to generate ages consistent with well-constrained stratigraphy, including Early and Late Cretaceous specimens and Middle to Late Miocene fossils. An initial study of a Zalmoxes dinosaur fibula from the late Cretaceous deposits of the Haţeg intramontane basin in western Romania yielded a U-Pb isochron age of fossilization of 74.4 ± 5.2 Ma. Subsequent analyses of an Early Cretaceous Hadrosaurid from Wyoming and a Late Miocene crocodilian coprolite from North Carolina have demonstrated the potential for this technique to be applicable across a variety of geologic questions. The prospect of better constraining the stratigraphic ages of vertebrates and their implications in our understanding of the timings of speciation and extinction events may make this an invaluable new tool in interpreting Earth’s history.