Cretaceous crab colonization
Freshwater and terrestrial crabs are thought to have diverged from their marine relatives during the Cretaceous, with phylogenetic studies suggesting that freshwater crabs emerged about 130 million years ago. However, fossil evidence to support their colonisation of non-marine environments at this time is limited. Now, Javier Luque at Harvard University, USA, and colleagues, report the discovery of a previously unknown crab species, Cretapsara athanata, which lived during the Late Cretaceous, about 100 million years ago.
This newly discovered species is a ‘true crab’, an early example of a modern-looking crab. It is preserved in amber found in rocks from Myanmar, Southeast Asia, which is unusual because most fossils preserved in amber are insects – in fact, this remarkable specimen is the first known example of a true crab found in amber. The fossil is exceptionally well preserved: micro-computed tomography (CT) digital reconstructions reveal eyestalks, antennae, and limbs all present. While its physical characteristics differ somewhat from present-day known crabs, the superficial similarities are remarkable.
Other material within the amber, such as carbonised wood fibres that potentially indicate a forest-floor setting, imply that this crab may have lived in a freshwater or brackish environment, and may even have been fully terrestrial. Cretapsara athanata therefore demonstrates that crabs colonised non-marine environments by the Late Cretaceous period, bridging the gap between the fossil and phylogenetic record.
• Science Advances 7, 43 (2021); doi.org/10.1126/sciadv.abj5689
Stephen McHugh, Research and Administrative Support Officer at the Irish Centre for Research in Applied Geosciences, Dublin