A new species of Pachyarmatherium (Xenarthra: Cingulata) from the late Pleistocene of northeastern Brazil and its phylogenetic affinities

PORPINO DE OLIVERA, K.; FERNICOLA, J. C.; BERGQVIST, L. P.

Cleveland, Ohio, EEUU

Congreso; 68th Annual Meeting of the Society of Vertebrate Paleontology; 2008

Society of Vertebrate Paleontology

Pachyarmatherium is an enigmatic cingulate genus formerly recognized as a Dasypodoidea, but tentatively assigned to the poorly known subfamily Glypatatelinae (Glyptodontidae) by later authors. Pachyarmatherium remains are only known from the late Pliocenelate Pleistocene of United States and Costa Rica so far. Here we describe a new species belonging to this genus from the Late Pleistocene of northeastern Brazil. The specimens studied comprise several isolated osteoderms, carapace fragments and miscellaneous postcranial material. The new species differs from the North American Pachyarmatherium leiseyi in being larger and in having osteoderms with pentagonal, hexagonal and heptagonal shape (instead of only pentagonal and hexagonal), main figures with oblong and subrounded outline, in contrast to the typical polygonal pattern observed in P. leiseyi, and a larger number of peripheral figures. The several well-preserved postcranial elements assigned to this new taxon allowed testing the affinities of Pachyarmatherium within cingulates. Therefore, we conducted a cladistic analysis of 48 morphological postcranial characters scored for eleven cingulates (Pachyarmatherium, four dasypodids, one pampathere and five glyptodontids) and two pilosans used as outgroup taxa. In the most parsimonious topology obtained, Pachyarmatherium is the sister-group to a clade including Pampatheriidae and Glyptodontidae. This result contradicts the previous tentative allocation of Pachyarmatherium within Glyptodontidae, and indicates that the glyptodontlike characters of the carapace and osteoderms of Pachyarmatherium (thick osteoderms and lack of movable bands) are homoplasies shared with glyptodonts. Finally, we note that the morphological evidence from the external ornamentation of osteoderms does not offer support for the placement of Pachyarmatherium within Glyptatelinae.