Sobre la posición filogenética de un ejemplar particular de Panochthus (Xenarthra, Glyptodontidae): análisis basado exclusivamente en caracteres de la coraza dorsal

On the phylogenetic position of a particular specimen of Panochthus (Xenarthra, Glyptodontidae): an analysis based exclusively on characteristics of the dorsal carapace. The monophyly of Xenarthra is supported by morphological and molecular characters, ancient DNA and collagen. Phylogenetic work also supports the idea of a common ancestor for the Cingulata; Glyptodontidae is considered a natural group too; this also occurs with the genus Panochthus, which includes eight species. The phylogenetic relationships of a peculiar specimen UATF-V s/n, assigned to Panochthus sp. were examined through a cladistic analysis carried out exclusively with characters from the dorsal carapace. A maximum parsimony tree with L = 49, CI = 0.84 and IR = 0.74 was obtained through the analysis of a matrix of 14 taxa and 29 characters. The cladogram comprises two large groups: node A includes Nopachtus coagmentatus, N. cabrerai, Propanochthus bullifer, Phlyctaenopyga ameghini; and node B contains Glyptodon reticulatus, Hoplophorus euphractus, Neosclerocalyptus ornatus, Panochthus intermedius, P. subintermedius, P. tuberculatus, P. greslebini, P. hipsilis and UATF-V s/n. The specimen UATF-V s/n is positioned as the sister taxon of all Panochthus spp., having most plesiomorphic characters than other species of the genus. Glyptodon reticulatus appears as the sister group of Panochthus, presenting osteoderms of the mid-dorsal region with a reticular pattern. The characteristic of these osteoderms without a central figure is shared with G. reticulatus and Neuryurus trabeculatus; this feature is interpreted as an evolutionary convergence. The exclusive feature of Panochthus is that the mid-dorsal region and the anterior part of the mid-lateral region of the dorsal carapace are formed by ornate osteoderms following a reticular pattern. Keywords: Glyptodontidae, Panochthus, phylogeny, dorsal carapace, osteoderms, reticular pattern.