A recent study published in eLife reveals that the iconic sideways walking of crabs can be traced back to a single evolutionary moment approximately 200 million years ago. Researchers, led by Yuuki Kawabata from Nagasaki University in Japan, analyzed the movement of 50 species of true crabs and found that this unique locomotion likely evolved from a forward-walking ancestor. The sideways movement provides crabs with a significant advantage in evading predators, allowing them to quickly change direction. Out of the species studied, 35 primarily moved sideways, while 15 moved forward, indicating that this trait has largely remained unchanged across true crabs since its origin. The study highlights that while many body shapes in the animal kingdom evolve multiple times—a phenomenon known as carcinization—behavioral changes like sideways walking are rare. This trait may have contributed to the ecological success of true crabs, which have diversified into around 7,904 species inhabiting various environments globally. The researchers suggest that environmental factors during the Jurassic period, including the breakup of Pangaea and the expansion of shallow marine habitats, played a crucial role in the diversification of these species. Overall, this research enhances our understanding of animal locomotion and the evolutionary innovations that can lead to ecological success.