Crab in amber reveals an early colonization of nonmarine environments during the Cretaceous

Amber fossils provide snapshots of the anatomy, biology, and ecology of extinct organisms that are otherwise inaccessible. The best-known fossils in amber are terrestrial arthropods-principally insects-whereas aquatic organisms are rarely represented. Here, we present the first record of true crabs (Brachyura) in amber-from the Cretaceous of Myanmar [similar to 100 to 99 million years (Ma)]. The new fossil preserves large compound eyes, delicate mouthparts, and even gills. This modern-looking crab is nested within crown Eubrachyura, or higher true crabs, which includes the majority of brachyuran species living today. The fossil appears to have been trapped in a brackish or freshwater setting near a coastal to fluvio-estuarine environment, bridging the gap between the predicted molecular divergence of nonmarine crabs (similar to 130 Ma) and their younger fossil record (latest Cretaceous and Paleogene, similar to 75 to 50 Ma) while providing a reliable calibration point for molecular divergence time estimates for higher crown eubrachyurans.

Automated summary

Amber fossils provide valuable insights into the anatomy, biology, and ecology of extinct organisms. In this study, the first record of true crabs in amber from the Cretaceous of Myanmar is presented, shedding light on the evolutionary history of crabs and providing a calibration point for molecular divergence time estimates. The fossil, with its well-preserved features, bridges the gap between molecular divergence predictions and the fossil record, providing important information on the evolutionary timeline of higher crown eubrachyurans.