For generations, paleontologists have wrestled with a deceptively simple question: when holding an ancient bone, how does one know whether it belonged to a young creature or a distinct species entirely? James Napoli, a researcher at Stony Brook University, has proposed an answer rooted not in the bones that change, but in the anatomical signatures that never do — the pathways of blood vessels, nerves, and the interlocking architecture of skulls, all established before birth and unchanged through a lifetime. Published this month in Paleobiology, his framework offers the field something rare: a