title: The Dance of Tusks: Rediscovery of Lower Incisors in the Pan-American Proboscidean Cuvieronius hyodon Revises Incisor Evolution in Elephantimorpha.
abstract: The incisors of proboscideans (tusks and tushes) are one of the most important feature in conservation, ecology and evolutionary history of these mammals. Although the absence of upper incisors is rare in proboscideans (occurring only in deinotheres), the independent losses of lower incisors are recognized for most of its lineages (dibelodont condition). The presence of lower incisors in the Pan-American gomphothere Cuvieronius hyodon was reported a few times in literature, but it was neglected in systematic studies. We analyzed several specimens of Cuvieronius hyodon from the Americas and recognized that immature individuals had lower incisors during very early post-natal developmental stages. Subsequently, these are lost and lower incisors alveoli close during later developmental stages, before maturity. Moreover, for the first time in a formal cladistic analysis of non-amebelodontine trilophodont gomphotheres, Rhynchotherium and Cuvieronius were recovered as sister-taxa. Among several non-ambiguous synapomorphies, the presence of lower incisors diagnoses this clade. We recognize that the presence of lower incisors in Cuvieronius and Rhynchotherium is an unique case of taxic atavism among the Elephantimorpha, since these structures are lost at the origin of the ingroup. The rediscovery of the lower incisors in Cuvieronius hyodon, their ontogenetic interpretation and the inclusion of this feature in a revised phylogenetic analysis of trilophodont gomphotheres brought a better understanding for the evolutionary history of these proboscideans.
authors.affiliation: Laboratório de Mastozoologia, Departamento de Zoologia, Instituto de Biociências, Universidade Federal do Estado do Rio de Janeiro, Av. Pasteur, 458, 501, Urca, CEP 22290-240, Rio de Janeiro, Brazil.|Programa de Pós-graduação em Ciências Biológicas (Zoologia), Museu Nacional/UFRJ, Quinta da Boa Vista, CEP 20940-040, Rio de Janeiro, Brazil.
authors.forename: Dimila
authors.initials: D
authors.lastname: Mothé
authors.affiliation: Dipartimento di Scienze della Terra e Museo di Storia Naturale, Sez. di Geologia e Paleontologia, Università di Firenze, via G. La Pira 4, I-50121 Firenze, Italy.
authors.forename: Marco P
authors.initials: MP
authors.lastname: Ferretti
authors.affiliation: Laboratório de Mastozoologia, Departamento de Zoologia, Instituto de Biociências, Universidade Federal do Estado do Rio de Janeiro, Av. Pasteur, 458, 501, Urca, CEP 22290-240, Rio de Janeiro, Brazil.|Programa de Pós-graduação em Biodiversidade Neotropical, Instituto de Biociências, Universidade Federal do Estado do Rio de Janeiro, Av. Pasteur, 458, 501, Urca, CEP 22290-240, Rio de Janeiro, Brazil.
authors.forename: Leonardo S
authors.initials: LS
authors.lastname: Avilla
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004777:Environment; D005399:Fishes / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics; D005580:Fossils; D007180:Incisor / Q000033:anatomy & histology; D010163:Paleontology; D010802:Phylogeny