Earliest Complete Fossil from History’s Most Successful Mammal Discovered

The fossil of Rugosodon eurasiaticus, preserved in two shale slabs

The fossil of Rugosodon eurasiaticus, preserved in two shale slabs

Zhe-Xi Luo, who recently discovered a fossil of an evolutionary predecessor to mammals, is back with another discovery, this time the earliest complete fossil of a fast-running, agile omnivore similar to modern rodents. Named Rugosodon eurasiaticus, this animal displayed key adaptations that allowed a group of early mammals called multituberculates to be the most abundant mammal during the Mesozoic Era. Kevin Jiang has more at the UChicago News site:

Rugosodon eurasiaticus, image by April Isch

Rugosodon eurasiaticus, image by April Isch

Of particular note are its surprisingly mobile and flexible ankle bones, which suggest that Rugosodon was a fast-running and agile mammal that mostly lived on the ground. This skeletal feature is thought to be the anatomical basis for the versatile and diverse locomotor adaptations, ranging from tree climbing to tunnel digging, which later multituberculates possessed.

Rugosodon draws its name from its rugose teeth, which were ornamented by numerous ridges and wrinkles. Its dental features are evidence that it was a versatile omnivore that fed on the leaves and seeds of gymnosperm plants and ferns, as well as worms and insects. Interestingly, this indicates that the later rise of numerous herbivorous multituberculates originated from an omnivorous ancestor.

Luo and his colleagues published their findings in the Aug. 16 issue of Science. Their previous discovery of the early proto-mammal Megaconus mammaliaformis was published in the Aug. 8 issue of Nature.

The Rugosodon discovery has been covered widely in national and international media, including:

Yuan C.X., Ji Q., Meng Q.J., Tabrum A.R. & Luo Z.X. (2013). Earliest Evolution of Multituberculate Mammals Revealed by a New Jurassic Fossil, Science, 341 (6147) 779-783. DOI:

About Matt Wood (514 Articles)

Matt Wood is a senior science writer at the University of Chicago Medicine and nonfiction editor for Another Chicago Magazine.

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