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A new study analyzing a 100-million-year-old fossil humerus bone of *Kryoryctes cadburyi*, a monotreme ancestor, reveals internal bone structure similar to the aquatic platypus. This suggests that the common ancestor of platypuses and echidnas was at least partially aquatic, contradicting previous assumptions based on external bone structure. The research, published in the Proceedings of the National Academy of Sciences, indicates the platypus's amphibious lifestyle originated much earlier than previously thought, while echidnas later adapted to a fully terrestrial life. This discovery provides crucial insights into early mammalian evolution.

Prepared by Olivia Bennett and reviewed by editorial team.