Stable isotopes of carbon and hydrogen in amber fossils shed light on insect ecology and habitats in deep time

Amber is a natural polymer composed mainly of terpenoids, which provide carbon and hydrogen for stable isotope analyses. The isotope toolkit applied to amber is similar to ecological studies in modern forests based on leaves and wood, but with a larger time component. Isotope analyses in amber research have expanded beyond fingerprinting deposits and their source areas. Carbon isotopes are currently being used to test for variation in CO2 uptake by ancient plants (e.g., stress effects) as well as changes in atmpsheric composition through time. Hydrogen isotopes are used to examine water sources accessed by ancient forests—delineating catchment areas for deposits or tracking coastline movements over time. When data from these two isotope systems are combined, they allow palaeontologists to examine how amber deposits are formed (e.g., storm damage, insect attacks), and how insect habitat preferences may have changed over time. We are currently analyzing amber from dinosaur bonebeds. This allows us to see how forest habitats changed leading up to the Cretaceous-Paleogene extinction event, and how amber data compare to a wider range of proxies in the fossil record. We are also applying stable isotope data to ‘Wheeler’s Dilemma’, the unusual occurrence of both temperate and tropical insects within the same amber deposit during the Eocene (~45 Ma). By analyzing amber surrounding ants or beetles with these modern distributions, we can test if they coexisted due to reduced seasonality, or if amber samples a wider range of habitats or time than initially thought.