Synchrotron X-ray scans have overturned the long-standing interpretation of Westlothiana lizziae, a small Carboniferous fossil once regarded as one of the earliest reptile-like land vertebrates. Hidden inside the crushed fossil were internal gill structures, a primitive skull and a heavily toothed mouth, placing the animal far outside the amniote lineage and pointing to an aquatic or amphibious lifestyle. Its surprisingly advanced feet and claw-like toe bones show that several adaptations once associated with reptiles evolved earlier among more primitive tetrapods, complicating recent claims based on ancient clawed footprints. For more than three decades, a tiny Scottish fossil helped scientists tell the story of vertebrates moving permanently onto land. New images hidden inside the rock have now transformed that story. Westlothiana lizziae, nicknamed “Lizzie,” was once described as the earliest known reptile and later placed near the ancestry of amniotes. That enormous group eventually produced reptiles, birds and mammals, including humans. Synchrotron X-ray scans have now exposed anatomy invisible when the crushed fossil was first studied. Instead of an early land-adapted amniote, researchers found an animal …