Pachyarmatherium (Xenarthra, Cingulata) remains from the Late Pleistocene of Northeastern Brazil and its phylogenetic affinities

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

Simposio; VI Simposio Brasileiro de Paleontologia de Vertebrados; 2008

Pachyarmatherium is an enigmatic cingulate genus known so far from the late Pliocene-early Pleistocene of United States of America and Costa Rica and for the first time recorded in Brazil. It was formerly recognized as a dasypodoid, but tentatively assigned to the poorly known subfamily Glypatatelinae (Glyptodontidae) by later authors. Here we present new material assigned to Pachyarmatherium from the Late Pleistocene of northeastern Brazil. The studied specimens, which includes several isolated osteoderms, carapace fragments and miscellaneous postcranial material, were recovered in late 60s from one of the largest caves of Lajedo da Escada (5°14’31”S and 37°44’20”W, Baraúna city, Rio Grande do Norte State), a large carbonatic outcrop of Jandaíra Formation (Upper Cretaceous, Potiguar Basin) with an area of 5 km2 comprising a wide carstic pavement where small caves were developed. The postcranial elements differ from the North American Pachyarmatherium leiseyi in being larger. The osteoderms are also larger than in P. leiseyi, and some of them also differ from this species in having heptagonal shape, main figures with oblong and subrounded outline (instead of polygonal solely), and a larger number of peripheral figures. In order to clarify the affinities of Pachyarmatherium, a matrix of 48 postcranial characters scored for eleven cingulates (four dasypodids, one pampathere, five glyptodontids plus Pachyarmatherium) and two Pilosa used as outgroup, was analyzed in PAUP 4.0b10 using the Branch and Bound algorithm. The character states were treated as unordered. In the most parsimonious topology obtained (tree length = 112, CI = 0.52, RI = 0.69) Pachyarmatherium is the sister-group to a clade including Pampatheriidae and Glyptodontidae. This sister-group relationship is well supported by bootstrap and Bremer support values (81 and 4 respectively) and is diagnosed by the following unambiguous synapomorphies: neural canal of atlas with ventral half wider than the dorsal half; transverse foramen of atlas positioned at an intermediate distance from the neural canal; head of the femur proximally oriented; great trochanter of femur laterally oriented; and wide transverse diameter of the proximal end of the tibia-fibula. This result contradicts the previous tentative allocation of Pachyarmatherium within Glyptodontidae, and indicates that the glyptodont-like characters of carapace and osteoderms (thick osteoderms and lack of movable bands) of Pachyarmatherium are homoplasies shared with glyptodonts. Moreover, the morphological evidence from the external ornamentation of osteoderms does not offer support for the placement of Pachyarmatherium within Glyptatelinae, because the only feature shared by glyptateline genera (Glyptatelus, Clypeotherium, and Neoglyptatelus) andPachyarmatherium – posterior displacement of the central figure – is also present in armadillos (e.g. Dasypus).