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Jaw roll and jaw yaw in early mammals

Nature volume 582, pages E6–E8 (2020)Cite this article

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Matters Arising to this article was published on 17 June 2020

The Original Article was published on 13 February 2019

Arising from B.-A. S. Bhullar et al. Nature https://doi.org/10.1038/s41586-019-0940-x (2019)

Recent fossil discoveries and methodological developments have triggered a renewed interest in the jaw mechanics of early mammals, and a study by Bhullar et al.1 is a welcome contribution to this resurgence. They find that the chewing cycle in the grey short-tailed opossum (Monodelphis domestica) includes considerable jaw roll (rotation around the long axis of a hemimandible), which produces ‘mortar-and-pestle’-like grinding by molars during occlusion. This is a fascinating result that contributes greatly to our understanding of the function of tribosphenic molars. However, I disagree with their hypothesis that the roll-dominated grinding in Monodelphis is an ancestral trait of therians (eutherians–placentals and metatherians–marsupials) that evolved in closely related early cladotherians (that is, non-therian cladotherians). Additional lines of evidence suggest that roll-dominated grinding is not a primitive trait in therians.

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Fig. 1: Tribosphenic molar evolution and the lack of a grinding surface in pre-therian molars.
Fig. 2: Evolutionary changes to the mammalian jaw that contradict the hypothesis that jaw roll grinding evolved in early cladotherians.

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No new data were generated in this study.

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  1. Department of Biology, University of Washington, Seattle, WA, USA

    David M. Grossnickle

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D.M.G. performed all work in this study.

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Correspondence to David M. Grossnickle.

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Grossnickle, D.M. Jaw roll and jaw yaw in early mammals. Nature 582, E6–E8 (2020). https://doi.org/10.1038/s41586-020-2365-y

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