In a surprising revelation, a study published in Systematic Biology on Nov. 6 disclosed that true crabs (Brachyura) have evolved to transition from sea to land and back multiple times over the last 100 million years. This extensive research, conducted by Harvard University’s Joanna Wolfe and her team, unraveled the dynamic history of true crabs, distinct from other crab-like crustaceans.
The findings suggest that true crabs, consisting of 7,600 species across 109 families, undertook this migration between seven and 17 times. Remarkably, on two or three occasions, some crabs even returned from land to the sea. This pattern contrasts with most arthropods, which left the ocean just once over 300 million years ago during terrestrialization.
To unveil this evolutionary journey, the researchers compiled extensive datasets for 333 true crab species from 88 families, considering both marine and non-marine groups. By utilizing mapping pathways, they classified each species based on their suitability for life on land, revealing a gradient of terrestriality.
The study challenges previous estimates, proposing that true crabs emerged much earlier—around 45 million years before thought, possibly dating back to the mid-Triassic period. This discovery aligns them with some of the earliest known dinosaurs. Convergent evolution, where different organisms independently develop similar traits, played a pivotal role in this remarkable journey.
Contrary to popular belief, the study emphasizes that most crabs are adapted to semi-terrestrial habitats, with only a specific group thriving on land. This research not only enhances our understanding of crab evolution but also highlights the complexity and adaptability of life forms in response to environmental changes over geological time scales.