Nature 379, 715 - 718 (22 February 1996); doi:10.1038/379715a0

Fossil evidence for the origin of the marsupial pattern of tooth replacement

Richard L. Cifelli^*, Timothy B. Rowe^†, W. Patrick Luckett^‡, James Banta^*, Reuben Reyes^† & Robert I. Howes^§

^* Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019, USA
^† Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA
^‡ Department of Anatomy, Medical Sciences Campus, University of Puerto Rico, P.O. Box 365067, San Juan, Puerto Rico 00936, USA
^§ Department of Anatomical Sciences, University of Oklahoma, P.O. Box 26901, Oklahoma City, Oklahoma 73190, USA

EXTANT marsupials are distinctive in their pattern of dental development¹, in that only one tooth is replaced postnatally in each jaw. Interpretation of this pattern for marsupials ancestrally is disputed^2–5, partly because ontogenetic data in fossils have been unobtainable. Here we present an ultra-high-resolution X-ray computed tomography (CT) study of the tiny fossil Alphadon, which represents the first evidence of dental development and replacement in a Mesozoic marsupial. In the known pattern of tooth replacement and development, Alphadon is identical to living marsupials, a derived similarity suggesting that this pattern is ancestral to Marsupialia, and that it was established by the Late Cretaceous, at least. This pattern has been correlated with some specialized aspects of marsupial lactation^1,6. Hence the presence of a marsupial pattern of tooth replacement in Alphadon provides indirect evidence that at least some specialized features of marsupial reproductive processes arose during the Mesozoic.

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