Paradoxomys cancrivorus Ameghino, 1885 (Rodentia, Hystricognathi, Erethizontidae): the first porcupine from the "Mesopotamian" (Late Miocene)

Paradoxomys cancrivorus Ameghino is redescribed on the basis of a cast of t he holotype, which is the only material currently available. The poorly pre served fossil and the fact that it was later lost, made the systematic hist ory of P. cancrivorus quite complicated. The characters visible in the cast are: 1) brachydont molars, with very convex walls and with the mesoflexid extended across three quarters of the width of the occlusal surface, 2) med ium size associated with this kind of molar and 3) sub-vertical symphysis. This allows us to refer it to the family Erethizontidae. Thus, it represent s the first porcupine for the "Mesopotamian". The incisor and mandibular mo rphologies suggest that P. cancrivorus may be more closely related to the r adiation of living porcupines than to the porcupines of the Late Oligocene- Middle Miocene Patagonian radiation. If the suggested affinities are correc t, they reinforce the biogeographic relationships of the "Mesopotamian" fau na with that of northern South America.