The oldest tribosphenic mammal from Laurasia (Purbeck Limestone Group, Berriasian, Cretaceous, UK) and its bearing on the ‘dual origin’ of Tribosphenida

We report the discovery of a tribosphenic molar in the Purbeck Limestone Group, Early Cretaceous, southern England, which we attribute to a new taxon, Tribactonodon bonfieldi gen.n. sp.n. In addition to the fact that it represents the oldest unequivocal tribosphenic mammal known from Laurasia, this tooth shows characters which have an important bearing on the distinction between the two infraclasses of Holotheria (Australosphenida and Boreosphenida) as defined by Luo et al., and which lead us to question the timing and place of their emergence.