Fossil mammal with reptile-like teeth changes picture of our evolution — SkimNews
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- Dongoconodon platycauda, a 120-million-year-old semi-aquatic mammal found in 2018 in Liaoning, China, weighed up to 190 grams, measured about 40 centimeters long, and resembled a nutria with a streamlined body, flattened swimming tail, and platypus-like webbed feet.
- The fossil's teeth were replaced multiple times across all four tooth classes — incisors, canines, premolar-like, and molar-like — making it the only known mammal to exhibit reptile-like polyphyodonty and directly challenging the textbook definition of mammalian diphyodonty.
- The specimen preserves one of the most complete Early Cretaceous mammalian middle-ear regions known, including Meckel's cartilage at an intermediate evolutionary stage where it had nearly detached from the lower jaw.
- Shundong Bi at Yunnan University says the discovery shows tooth replacement and middle-ear evolution were independent rather than a tightly linked suite of traits, demonstrating that early mammalian evolution was "considerably more flexible" than the traditional picture suggests.
- Mike Benton at the University of Bristol confirmed the team makes a good case for at least three sets of teeth, calling the specimen "quite late-occurring" for having retained reptilian ancestry features that other Mesozoic mammals had already lost by the end of the Triassic, roughly 201 million years ago.
- The study is published in Nature Communications (DOI: 10.1038/s41467-026-77339-w).
Why it matters: The find directly overturns a century-old textbook rule that mammals replace teeth only once (diphyodonty) by showing a Cretaceous mammal replaced teeth like a reptile across every tooth class. The independent evolution of teeth and ear bones forces a rewrite of how mammalian dental and auditory transitions are taught, reframing early mammal diversification as a set of parallel evolutionary experiments rather than a single progressive transition.
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