NATURE BRIEFING 24 April 2026 Hearts that didn’t beat were quickly overtaken by cancer cells in mice. Plus, huge octopuses might have ruled the ancient seas and how geopolitics is affecting huge health data sets. You have full access to this article via your institution. Hello Nature readers, would you like to get this Briefing in your inbox free every day? Sign up here . Artist’s impression of an extinct Nanaimoteuthis species, often called krakens, which could have rivalled large marine reptiles in terms of size. Credit: Masato Hattori/Science Photo Library Krakens might have ruled the ancient seas In the age of dinosaurs, giant octopuses — sometimes named krakens after the mythological monsters — might have grown to nearly 19 metres in length. The estimate is based on fossilized jaws, which researchers say show patterns of wear that came from devouring animals that had hard shells and skeletons.…