Formerly considered to be related with Nectomys, Sigmodontomys, Megalomys, or Oryzomys, it is now placed in then genus Mindomys, but its relationships remain obscure; some evidence supports a placement near Oecomys or as a basal member of Oryzomyini.
Mindomys hammondi is known only from Ecuador, where it occurs in montane forest; a record from the Amazon basin lowlands is dubious.
[9] In 1913, Oldfield Thomas of the British Museum of Natural History (BMNH) in London published the first description of Mindomys hammondi, using two specimens collected at Mindo in Pichincha Province, Ecuador, in the same year by Gilbert Hammond.
[10] In his 1941 review The Families and Genera of Living Rodents, Sir John Ellerman retained N. hammondi as a species of Nectomys, but noted that the features of its teeth were atypical for the genus, as "the cusps appear to show no tendency to become suppressed.
He now considered the latter to be a species of Oryzomys (at the time a large genus that included most of the current members of the tribe Oryzomyini), but distinctive enough to be placed in its own subgenus.
[17] In 1982, Steadman and Ray mentioned the animal in passing under the name Macruroryzomys hammondi and reaffirmed its relationship to Megalomys.
[18] In the 2005 third edition of Mammal Species of the World, Guy Musser and Michael Carleton listed O. hammondi as an Oryzomys of obscure affinities, but suggested that it may be related to Megalomys.
[8] In 2006, Marcelo Weksler published a large-scale cladistic analysis of Oryzomyini ("rice rats"), the group (tribe) to which hammondi and the related species mentioned above belong.
[19] Traits of O. hammondi that supported the latter placement include: a relatively short palate that does not extend behind the maxillary bones; simple posterolateral palatal pits; absence of a capsular process (a raising of the bone of the mandible, or lower jaw, at the back end of the incisor); and presence of the posteroloph on the upper third molar (a crest at the back of the tooth).
[7] Noting its "enigmatic distribution" and uncertain but perhaps basal position within Oryzomyini, they labeled the species an "extraordinary rat" worthy of continued inquiry.
Sigmodontinae itself is the largest subfamily of the family Cricetidae, other members of which include voles, lemmings, hamsters, and deermice, all mainly from Eurasia and North America.
[3] The squamosal bone lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity, a defining character of oryzomyines.
[45] Between 1913 and 1980, eight specimens were collected at Mindo,[46] a "tiny agricultural community"[15] at 1,264 m (4,147 ft) elevation in Pichincha Province, northwestern Ecuador.
Another specimen is labeled as having been collected on July 27, 1929, by the Olalla family of professional collectors in Concepción, a locality in the Amazon basin lowlands of Napo Province, around 300 to 500 m (980 to 1,640 ft) above sea level.
If this record is correct, Mindomys would be unique among small, non-flying mammals native to Ecuador in occurring at relatively low elevations on both sides of the Andes.
[29] Citing unpublished work by Tirira and Percequillo, the 2009 IUCN Red List reports that Mindomys is known from eleven specimens collected at four localities in northwestern Ecuador, and that its altitudinal range extends from 1,200 to 2,700 m (3,900 to 8,900 ft) above sea level, but does not give details.
[29] In 1999, Eisenberg and Redford suggested that the species may live in trees;[49] in 2007, Tirira agreed, citing the animal's broad feet.