A polyphyodont, semiaquatic eutriconodontan mammal from the Early Cretaceous of China.

A nearly complete Early Cretaceous eutriconodontan mammal exhibits polyphyodonty, the only known Mesozoic mammal with multiple generations of teeth at some loci.

• Why it matters: Understanding dental replacement patterns in ancient mammals is crucial for insights into mammalian evolution, especially regarding traits like precise occlusion and growth.
• What they did: The researchers examined a fossil with four tooth types showing evidence of polyphyodonty, along with adaptations for semiaquatic life, including webbed limbs and a flattened tail.
• The result: This discovery suggests reappearance of polyphyodonty in some Mesozoic mammals, linked to their ecological niche and diet, providing new perspectives on mammalian developmental and functional evolution.