Alcidedorbignya inopinata(Mammalia: Pantodonta) from the Early Paleocene of Bolivia: phylogenetic and paleobiogeographic implications

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Abstract
Alcidedorbignya inopinataMuizon and Marshall is a primitive pantodont from the Early Paleocene of Tiupampa, Department of Cochabamba, in the “Cordillera Oriental” of south-central Bolivia. It is known by almost complete upper and lower dentitions, which are described in detail. The occurrence of abundant juvenile specimens allows a study of tooth replacement. The molars ofAlcidedorbignya inopinataare primitive for a pantodont but they show the characteristic synapomorphy of the group, which is the presence of a V-shaped ectoloph of P3-4. However, the paracone and the metacone ofA. inopinataare separated at their bases, a feature absent in the Bemalambdidae andHarpyodus, which have connate to semi-connate paracone and metacone. Because of this character,A. inopinata, although the oldest, is not the most primitive pantodont. However,A. inopinata, as in bemalambdids andHarpyodus, does not have a mesostyle on M1-2/ or a strongly V-shaped centrocrista, which are found in all other pantodonts. For this reason,Alcidedorbignya inopinatais removed from the Pantolambdidae (which are too specialized) and referred to the new monotypic family Alcidedorbignyidae. The family Wangliidae Van Valen, 1988, is not accepted here and the genusWangliais regarded as a junior synonym ofHarpyodus; the latter includes the two speciesH. eurosandH. decorus.Analysis of pantodont origins leads to the conclusion that didelphodontines constitute the best potential sister-group; however, no synapomorphy could be found to substantiate this hypothesis.Alcidedorbignya inopinatais the first pantodont known from a southern continent and, being the oldest, it raises a discussion on the paleobiogeographic history of the group.