Genus level The genus
Proechimys is the sister group to the genus
Hoplomys (the armored rat). In turn, these two taxa share evolutionary affinities with other
Myocastorini genera:
Callistomys (the painted tree-rat) and
Myocastor (the coypu or nutria) on the one hand, and
Thrichomys on the other hand.
Species level Reconstructing the systematics and phylogeny of
Proechimys species have been greatly hampered by extreme levels of within- and among-population character variability. and mitochondrial DNA sequences have been used, and allowed to group species into major clades but whose interrelationships remain unresolved. The different groups of species can be diagnosed as follows. • Group
semispinosus: it contains two species,
Proechimys semispinosus, — with its widespread range, from Central America south from Honduras along the west coast of Colombia and Ecuador — and
P. oconnelli, with a more limited range, east of the Cordillera Oriental in the north-western Amazon. • Group
longicaudatus: it contains the three species
Proechimys longicaudatus,
P. brevicauda, and
P. cuvieri, united by lyrate and strongly fanged incisive foramina, and deep groves extending onto the anterior palate. They range from the lowland rainforest of the Guianan region and Amazon basin to dry forests of eastern Bolivia, northern Paraguay, and central Brazil. • Group
guyannensis: it contains the two species
Proechimys guyannensis, and
P. roberti, showing a plantar surface of hindfeet with six pads, and distributed mostly in the Guianan region, eastern Amazonia, and extending south into central Brazil. • Group
trinitatus: it contains the eight species
Proechimys trinitatus,
P. mincae,
P. guairae,
P. poliopus,
P. magdalenae,
P. chrysaeolus,
P. urichi, and
P. hoplomyoides. These taxa possess large and open incisive foramina, and simplified cheek teeth. • Group
goeldii: it contains the three species
Proechimys steerei,
P. quadruplicatus, and
P. goeldii, united by a uniformly large body size. Members of this group most commonly inhabit the seasonally inundated
várzea or
igapó lowland forests of the Amazon basin. • Group
gardneri: it contains the three species
Proechimys gardneri,
P. pattoni, and
P. kulinae, characterized by short head and body length — less than . They are distributed in western Amazonia, but with non-overlapping ranges as all three species replace one another along the length of the
Juruá River or on its opposite banks. ==Distribution==