New remains of Neotropical bunodont litopterns and the systematics of Megadolodinae (Mammalia: Litopterna)

Litopterna is one the most diverse and long–lived clades of South American native ungulates. Megadolodus and Neodolodus are bunodont litoptern genera recorded in the middle Miocene tropical faunistic assemblage of La Venta (Colombia). Both taxa were initially identified as didolodontid ‘condylarths’, but later reclassified into Proterotheriidae, within Litopterna. Previous studies proposed their inclusion within Proterotheriidae, but possible affinities with early litopterns and didolodontids have not been properly tested in phylogenetic analyses. We report new material of Megadolodus and Neodolodus from La Venta, which document new aspects of their upper and lower dentition, and we reassess their phylogenetic relationships with Litopterna and Didolodontidae. Using pre-existing matrices, we tested two alternative approaches of character construction for serial characters on the dentition in our phylogenetic analyses. Based on previously known and new fossil material, our analyses with both coding approaches support a close relationship between Megadolodus and Neodolodus, within Litopterna, and do not support a close relationship with Didolodontidae. At a less inclusive level, the relationships of Megadolodinae within Litopterna vary depending on the coding approach used. However, all of our analyses unambiguously support the monophyly of Megadolodinae as a clade of Neotropical bunodont litopterns. While the discovery of these new remains enlightens part of the litoptern phylogeny, the sensitivity of our analyses to coding approaches further highlights the importance of critical evaluation of character construction in morphological phylogenetics.