When the ancestors of terrestrial life on Earth crawled or slithered out of the sea, they formed the starting point for many of the world’s species. Some of these species even made the return journey back into the water from a life on land. Now, a new study has taken a closer look at explaining when and how this happened, and which species went back to a fully aquatic lifestyle. The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.

To do this, the team behind the study looked in finer detail at hundreds of museum specimens at the Yale Peabody Museum and other institutions, taking more than 11,000 new measurements, photographs, and CT scans. They even used a statistical test developed during World War II to work out the probability of featu

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