title: Evolutionary patterns in the dentition of duplicidentata (mammalia) and a novel trend in the molarization of premolars.
abstract: BACKGROUND
  The cusp homology of Lagomorpha has long been problematic largely because their teeth are highly derived relative to their more typically tribosphenic ancestors. Within this context, the lagomorph central cusp has been particularly difficult to homologize with other tribosphenic cusps; authors have previously considered it the paracone, protocone, metacone, amphicone, or an entirely new cusp.
  
  
  RESULTS
  Here we present newly described fossil duplicidentates (Lagomorpha and Mimotonidae) in the context of a well-constrained phylogeny to establish a nomenclatural system for cusps based on the tribosphenic pattern. We show that the central cusp of lagomorphs is homologous with the metaconule of other mammals. We also show that the buccal acquisition of a second cusp on the premolars (molarization) within duplicidentates is atypical with respect to other mammalian lineages; within the earliest lagomorphs, a second buccal cusp is added mesially to an isolated buccal cusp.
  
  
  CONCLUSIONS
  The distal shift of the 'ancestral' paracone within early duplicidentates amounts to the changing of a paracone into a metacone in these lineages. For this reason, we support a strictly topological approach to cusp names, and suggest a discontinuity in nomenclature to capture the complexity of the interplay between evolutionary history and the developmental process that have produced cusp patterns in duplicidentates.
authors.affiliation: Department of Anatomy, Western University of Health Sciences, Pomona, California, USA. bkraatz@westernu.edu
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kraatz
authors.forename: Jin
authors.initials: J
authors.lastname: Meng
authors.forename: Marcelo
authors.initials: M
authors.lastname: Weksler
authors.forename: Chuankui
authors.initials: C
authors.lastname: Li
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003817:Dentition; D005580:Fossils; D007793:Lagomorpha / Q000145:classification; D008322:Mammals / Q000145:classification* / Q000254:growth & development; D008963:Molar / Q000033:anatomy & histology / Q000254:growth & development*; D010161:Paleodontology; D010802:Phylogeny