What is "pennatomys"

Pennatomys nivalis is an extinct oryzomyine rodent from the islands of Sint Eustatius, Saint Kitts, and Nevis in the Lesser Antilles. The only species in the genus Pennatomys, it is known from skeletal remains found in Amerindian archeological sites on all three islands, with dates ranging from 790–520 BCE to 900–1200 CE. No live specimens are known, but there are several historical records of rodents from Saint Kitts and Nevis that could conceivably refer to Pennatomys. The animal apparently belongs to a group within the tribe Oryzomyini that includes many other island-dwelling species.

Pennatomys nivalis was a medium-sized species without many distinctive adaptations. The nasal bones were short and blunt-ended. The zygomatic plate, a bony plate at the side of the skull, was broad. The bony palate was long and flat. The root of the lower incisor was housed in a bony protuberance, the capsular process. The molars were low-crowned and possess accessory crests such as mesolophs. The upper molars all had three roots.