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.

Oryzomyini, also known as rice rats, is a diverse grouping of North, Central, and South American rodents within the family Cricetidae.

Branch[3] and were later found in abundance in Amerindian archeological sites on nearby Nevis and Sint Eustatius.

[4] The rice rat of these islands was formally described and named as Pennatomys nivalis in a 2010 article by zoologist Samuel Turvey and coworkers.

This clade contains a number of species occurring only on islands – including members of Aegialomys, Megalomys, Nesoryzomys, Noronhomys, Oryzomys, and Pennatomys.

Turvey and colleagues suggested that this is related to the high proportion of semiaquatic species in clade D – most other oryzomyines are forest dwellers.

[10] It is one of several tribes within the subfamily Sigmodontinae of the family Cricetidae, which encompasses hundreds of other species of mainly small rodents, distributed chiefly in Eurasia and the Americas.

The molars are bunodont (with the cusps higher than the connecting crests) and brachyodont (low-crowned) and have the inter-cusp valleys on the labial (outer) sides closed by a cingulum (shelf).

On M2, there is no protoflexus (an indentation in front of the protocone, which on this tooth is the frontmost cusp) and the valley between the paracone and the mesoloph, the mesoflexus, is not divided into two pieces by a paracone–mesoloph connection.

[16] The mesoloph is present on M3, but the posteroloph, a crest at the back of the tooth, is absent or vestigial, as is the hypoflexus (the valley between the protocone and the cusp behind it, the hypocone).

[4] Unambiguous historical records of Pennatomys are lacking, but there are some references to Saint Kitts and Nevis rodents that may relate to it.

George Percy reported on the presence of "great store of Conies"[Note 1] on Nevis around 1606, probably a reference to the agoutis (Dasyprocta) that have been introduced throughout the Lesser Antilles.

There are anecdotal records of unusual rats on Nevis up to recent times; these were reportedly eaten by the Islanders until the 1930s.