Early Cretaceous Origin of Pteropods Suggests Their Resilience to Ocean Acidification

Pteropods are a group of planktonic gastropods that are widely regarded as biological indicators for monitoring the impact of ocean acidification. Their thin shells of aragonite, a metastable form of calcium carbonate, are highly sensitive to changes in ocean chemistry. To predict the responses of pteropods to current climate change, we need to accurately reconstruct their evolutionary history to infer their capacity to adapt to ocean change. Here a phylogenomic dataset (2654 genes, 28 taxa) and fossil evidence are used to resolve the phylogeny and timing of pteropod evolution. In agreement with traditional taxonomy, but resolved with molecular data for the first time, our results indicate a division between Thecosomata or 'sea butterflies' (mostly shelled, mucus web feeders) and Gymnosomata or 'sea angels' (unshelled, active predators). These two lineages diverged in the Early Cretaceous, and therefore both survived major global change events such as the Paleocene Eocene Thermal Maximum, the closest analogue to modern-day ocean warming and acidification. These results indicate resilience of aragonitic calcifiers to ocean acidification over evolutionary timescales.