Letter

Nature 450, 93-97 (1 November 2007) | doi:10.1038/nature06221; Received 3 April 2007; Accepted 3 September 2007

Convergent dental adaptations in pseudo-tribosphenic and tribosphenic mammals

Zhe-Xi Luo1, Qiang Ji2 & Chong-Xi Yuan2

  1. Carnegie Museum of Natural History, Pittsburgh, Pennsylvania 15213, USA
  2. Chinese Academy of Geological Sciences, Beijing 100037, China

Correspondence to: Zhe-Xi Luo1 Correspondence and requests for materials should be addressed to Z.-X.L. (Email: luoz@carnegiemnh.org).

Tribosphenic molars of basal marsupials and placentals are a major adaptation, with the protocone (pestle) of the upper molar crushing and grinding in the talonid basin (mortar) on the lower molar1, 2, 3, 4. The extinct pseudo-tribosphenic mammals have a reversed tribosphenic molar in which a pseudo-talonid is anterior to the trigonid, to receive the pseudo-protocone of the upper molar. The pseudo-protocone is analogous to the protocone, but the anteriorly placed pseudo-talonid is opposite to the posterior talonid basin of true tribosphenic mammals5, 6, 7. Here we describe a mammal of the Middle Jurassic period with highly derived pseudo-tribosphenic molars but predominantly primitive mandibular and skeletal features, and place it in a basal position in mammal phylogeny. Its shoulder girdle and limbs show fossorial features similar to those of mammaliaforms and monotremes, but different compared with those of the earliest-known Laurasian tribosphenic (boreosphenid) mammals. The find reveals a much greater range of dental evolution in Mesozoic mammals than in their extant descendants, and strengthens the hypothesis of homoplasy of 'tribosphenic-like' molars among mammals.

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