Scelidotheriine (Mammalia, Xenarthra) autopodial bones from the Pliocene (Chapadmalalan) of Cordoba province, Argentina, and their systematic implications

Here, we report new autopodial material belonging to a scelidotheriine sloth from the Pliocene (Chapadmalalan) of Rio de La Cruz valley, Cordoba province, Argentina. The epiphyseal suture fusion in metacarpals III and IV indicates adult size; compared with other scelidotheriines, the preserved bones are slightly larger than in pre-Chapadmalalan taxa, but quite smaller than in post-Chapadmalalan taxa. The metacarpal III presents a distal carina longer relative to proximodistal length - from proximalmost point of proximal end to centre of carina - than in other scelidotheriines. The metacarpal IV shaft is dorsoventrally depressed, as in post-Chapadmalalan specimens of the genus Scelidotherium. Differences from the latter include a metacarpal III with a mostly saddle-shaped articular surface for metacarpal IV, and a metatarsal V with a strongly raised surface on the proximal end plantar surface. A phylogenetic analysis including 13 scelidotheriine and 5 outgroup terminals, and 173 characters supports close relationships with Scelidotherium. The size of the presently reported specimen likely matches the size range of material previously assigned to Scelidotherium parodii. The specimen probably represents the first autopodial remains reported for a Pliocene representative of that genus and raises the possibility that it belongs to the Chapadmalalan taxon, Scelidotherium parodii.

Automated summary

We report new autopodial material belonging to a scelidotheriine sloth from the Pliocene of Argentina. The bones indicate adult size and show differences compared to other scelidotheriines. Phylogenetic analysis supports a close relationship with Scelidotherium. This finding provides important clues for understanding the origin and evolution of Pliocene scelidotheriine sloths.