Hammond's Rice Rat
Encyclopedia
Mindomys hammondi, also known as Hammond's Rice Rat or Hammond's Oryzomys, is a species of rodent
in the tribe Oryzomyini
of family Cricetidae
. Formerly considered to be related with Nectomys
, Sigmodontomys
, Megalomys
, or Oryzomys
, it is now placed in its own 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 Amazonian lowlands is dubious. Reportedly, it lives on the ground and is associated with water; other suggest it lives in trees. A large, long-tailed, and long-whiskered rat, its fur is buff
above and abruptly lighter below. The front part of the skull (rostrum) is heavily built.
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 1913 by Gilbert Hammond. He named the species Nectomys hammondi, classifying it in the genus Nectomys
, which at the time included not only the large water rats currently placed in it, but also Sigmodontomys alfari and Oryzomys dimidiatus. He considered the animal to be most closely related to Nectomys russulus, a species he had himself described in 1897 and which is now recognized as a synonym
of Sigmodontomys alfari.
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." Reviewing the genus Nectomys in 1944, Philip Hershkovitz
listed N. hammondi among species of Nectomys incertae sedis
(of uncertain position), and considered its placement in Nectomys as dubious. Characters he listed as conflicting with a Nectomys identity of the species included the short hindfoot with a long fifth toe, the weakly developed posterolateral palatal pits
(perforations of the palate
near the third molars), and the orientation of the zygomatic plate
.
of N. hammondi. 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
. Noting that the species was "extremely long-tailed", he introduced the subgeneric name Macruroryzomys for hammondi. He also wrote that Oryzomys aphrastus (currently Sigmodontomys aphrastus), then known only from Costa Rica, may be the closest relative of hammondi.
In his 1962 Ph.D. thesis, Clayton Ray considered O. hammondi to be most closely related to Megalomys
, which includes giant rats from the Caribbean, and classified it as a member of the subgenus Megalomys of genus Oryzomys. In 1970, Hershkovitz treated the species in another publication and noted that his name Macruroryzomys was a nomen nudum
("naked name") because he had not explicitly mentioned characters differentiating it from other taxa in his 1948 publication. Nevertheless, he did not do anything to rectify the situation, and Macruroryzomys remains a nomen nudum. Hershkovitz rejected any relationship between O. hammondi and Nectomys or O. aphrastus and instead argued that O. hammondi was closely similar to Megalomys and may be close to the ancestor of Megalomys. In 1982, Steadman and Ray mentioned the animal in passing under the name Macruroryzomys hammondi and reaffirmed its relationship to Megalomys. 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.
analysis of Oryzomyini
("rice rats"), the group (tribe) to which hammondi and the related species mentioned above belong. He used both morphological and molecular characters, but had only morphological data for Oryzomys hammondi. The placement of the species in his results was unstable; some trees
placed it close to the tree rice rats, Oecomys
, within clade B and others placed it as an isolated lineage, basal
to all other Oryzomyini.
Traits of O. hammondi that supported the latter placement include: a relatively short palate that does not extend behind the maxilla
ry 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). In these characters, O. hammondi differs from many or most Oryzomyini and is similar to some species outside Oryzomyini, but all traits of O. hammondi are present in at least one other member of the tribe. Traits shared by O. hammondi and Oecomys included: tail with the same coloration above and below (unicolored); parietal bone
s extending to the sides of the skull; narrow zygomatic plate, without a zygomatic notch; posteroloph present on upper third molar; mesoflexus (a valley in the molar crown in front of the mesoloph crest) on upper second molar not divided in two.
In Weksler's analysis, species placed in Oryzomys did not form a coherent (monophyletic
) group, but instead were found at various positions across the oryzomyine tree, and he suggested that most of these species, including O. hammondi, should be placed in new genera. Later in 2006, Weksler and others described ten new genera for species formerly placed in Oryzomys, including Mindomys for hammondi. Noting its "enigmatic distribution" and uncertain but perhaps basal position within Oryzomyini, they labeled the species an "extraordinary rat" worthy of continued inquiry. The generic name
refers to Mindo, the type locality of M. hammondi.
Mindomys is now one of about 28 genera in the tribe Oryzomyini, which includes well over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands
and some of the Antilles
. Oryzomyini is one of several tribes recognized within the subfamily Sigmodontinae
, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae
, other members of which include vole
s, lemming
s, hamster
s, and deermice
, all mainly from Eurasia and North America.
(whiskers) are long. The very long tail is dark both above and below and has rectangular scales. The hindfeet are broad, with long, narrow digits. They have poorly developed ungual tuft
s, patches of hair between the digits and along the plantar margins. The squamae
, small structures resembling scales that cover the soles of the hindfeet in many oryzomyines, are indistinct. The fifth digit reaches to about half the length of the second phalange of the fourth. As in most oryzomyines, females have eight mammae. In specimens with published measurements, head and body length is 173 to 203 mm (6.8 to 8.0 in), tail length is 251 mm (9.9 in), hindfoot length is 41 to 42 mm (1.6 to 1.7 in), ear length is 18 mm (0.71 in), and greatest length of skull is 39.4 to 43.9 mm (1.55 to 1.73 in).
, the rostrum (front part) is large and robust. The nasal bone
s are short, not extending further back than the lacrimals
, and the premaxillaries extend about as far back as the nasals. The zygomatic plate is narrow and lacks a zygomatic notch, an extension of the plate at the front. The plate's back margin is level with the front of the first upper molar. The narrowest part of the interorbital region
, located between the eyes, is to the front and its margins exhibit strong beading. Various crests develop on the long braincase, especially in old animals. The parietal bones form part of the roof of the braincase and, unlike in some other rice rats, also extend to the sides of the braincase.
The incisive foramina
, perforations of the palate between the incisor
s and the molars, are short, not extending between the molars. The condition of the posterolateral palatal pits is variable, with some individuals having small pits and others having larger pits that may be recessed into a fossa (depression). The palate is moderately long, extending beyond the molars but not beyond the posterior margins of the maxillary bone. In most specimens, the roof of the mesopterygoid fossa, the gap behind the back of the palate, is not perforated by sphenopalatine vacuities
and thus it is fully ossified; if present, these vacuities are small. Mindomys lacks an alisphenoid strut
; in some other oryzomyines, this extension of the alisphenoid bone separates two openings (foramina
) in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. There are no openings in the mastoid bone. The squamosal bone
lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
, a defining character of oryzomyines.
In the mandible, the mental foramen
, an opening in the mandible just before the first molar, opens to the outside, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, join at a point below the first molar and do not extend forward beyond that point. There is no capsular process of the lower incisor, a trait Mindomys shares with only a few other oryzomyines.
are bunodont (with the cusps higher than the connecting crests) and brachydont
(low-crowned). On the upper first and second molar, the outer and inner valleys between the cusps and crests interpenetrate. Many accessory crests are present, including the mesolophs and mesolophids. The anterocone and anteroconid, the front cusps on the upper and lower first molar, are not divided into smaller outer and inner cusps. Unlike in Nectomys, Oryzomys, and Megalomys, the first upper and lower molars usually lack accessory roots, so that each of the three upper molars has two roots on the outer side and one on the inner side and each of the lower molars has one root at the front and one at the back.
, 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 Amazonian lowlands of Napo Province
, around 300 to 500 m (1000 to 1600 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. Furthermore, other collectors working in the same area in Napo have failed to find Mindomys, and the date the specimen was reportedly collected does not accord with the dates reported for the visit of the Olallas to Concepción, rendering its provenance dubious. There are two other locations named "Concepción" in northwestern Ecuador, and Diego Tirira suggested in 2007 that the specimen may instead be from one of these. Another specimen is known from Chaco, Imbabura Province
, at an altitude of 630 m (2070 ft).
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 1200 to 2700 m (3900 to 8900 ft) above sea level, but does not give details. The species occurs in moist, montane forest on the foothills of the western Andes.
Almost nothing is known of the biology of Mindomys. In 1999, Eisenberg and Redford suggested that the species may live in trees; in 2007, Tirira agreed, citing the animal's broad feet. Tirira also suggested that it is nocturnal (active during the night) and solitary and eats fruits, seeds, and insects. According to the 2009 IUCN Red List, it lives on the ground and "apparently has some affinity with water".
s, but has been recorded close to the protected forest of Mindo-Nambillo. It prefers well-conserved primary forest.
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
in the tribe Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
of family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
. Formerly considered to be related with Nectomys
Nectomys
Nectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...
, Sigmodontomys
Sigmodontomys
Sigmodontomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is related to Nectomys and Melanomys and was previously included in Nectomys. It includes two species, Sigmodontomys alfari and the much rarer Sigmodontomys aphrastus, but whether these are indeed each other's...
, Megalomys
Megalomys
Megalomys is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains four large rodents from various Caribbean islands, all of which are now extinct. The last species to survive was M...
, or Oryzomys
Oryzomys
Oryzomys is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
, it is now placed in its own genus, Mindomys, but its relationships remain obscure; some evidence supports a placement near Oecomys
Oecomys
Oecomys is a genus of rodent within the tribe Oryzomyini of family Cricetidae. It contains about 17 species, which live in trees and are distributed across forested parts of South America, extending into Panama and Trinidad.-Literature cited:...
or as a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of Oryzomyini.
Mindomys hammondi is known only from Ecuador, where it occurs in montane forest; a record from the Amazonian lowlands is dubious. Reportedly, it lives on the ground and is associated with water; other suggest it lives in trees. A large, long-tailed, and long-whiskered rat, its fur is buff
Buff (colour)
Buff is a pale yellow-brown colour that got its name from the colour of buff leather.Displayed on the right is the colour buff.EtymologyAccording to the Oxford English Dictionary, buff as a descriptor of a colour was first used in the London Gazette of 1686, describing a uniform to be "A Red Coat...
above and abruptly lighter below. The front part of the skull (rostrum) is heavily built.
Discovery and classification in Nectomys
In 1913, Oldfield ThomasOldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
of the British Museum of Natural History (BMNH) in London published the first description of Mindomys hammondi, using two specimens collected at Mindo
MINDO
MINDO, or Modified Intermediate Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Intermediate Neglect of Differential Overlap method of John Pople. It was developed by the group...
in Pichincha Province
Pichincha Province
Pichincha is a province of Ecuador located in the northern sierra region; its capital and largest city is Quito. It is bordered by Imbabura & Esmeraldas to the north, Cotopaxi & Santo Domingo de los Tsáchilas to the south, Napo & Sucumbíos to the east, and Esmeraldas & Santo Domingo de los...
, Ecuador, in 1913 by Gilbert Hammond. He named the species Nectomys hammondi, classifying it in the genus Nectomys
Nectomys
Nectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...
, which at the time included not only the large water rats currently placed in it, but also Sigmodontomys alfari and Oryzomys dimidiatus. He considered the animal to be most closely related to Nectomys russulus, a species he had himself described in 1897 and which is now recognized as a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of Sigmodontomys alfari.
In his 1941 review The Families and Genera of Living Rodents, Sir John Ellerman
Sir John Ellerman, 2nd Baronet
Sir John Reeves Ellerman, 2nd Baronet was an English shipowner, natural historian and philanthropist. The only son and heir of the English shipowner and investor John Ellerman, he was often said to be Britain's richest man...
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." Reviewing the genus Nectomys in 1944, Philip Hershkovitz
Philip Hershkovitz
Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...
listed N. hammondi among species of Nectomys incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
(of uncertain position), and considered its placement in Nectomys as dubious. Characters he listed as conflicting with a Nectomys identity of the species included the short hindfoot with a long fifth toe, the weakly developed posterolateral palatal pits
Posterolateral palatal pits
In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...
(perforations of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
near the third molars), and the orientation of the zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
.
Classification in Oryzomys
Hershkovitz published again on Nectomys in 1948 after examining additional material, including the holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of N. hammondi. He now considered the latter to be a species of Oryzomys
Oryzomys
Oryzomys is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
(at the time a large genus that included most of the current members of the tribe Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
), but distinctive enough to be placed in its own subgenus
Subgenus
In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
. Noting that the species was "extremely long-tailed", he introduced the subgeneric name Macruroryzomys for hammondi. He also wrote that Oryzomys aphrastus (currently Sigmodontomys aphrastus), then known only from Costa Rica, may be the closest relative of hammondi.
In his 1962 Ph.D. thesis, Clayton Ray considered O. hammondi to be most closely related to Megalomys
Megalomys
Megalomys is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains four large rodents from various Caribbean islands, all of which are now extinct. The last species to survive was M...
, which includes giant rats from the Caribbean, and classified it as a member of the subgenus Megalomys of genus Oryzomys. In 1970, Hershkovitz treated the species in another publication and noted that his name Macruroryzomys was a nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
("naked name") because he had not explicitly mentioned characters differentiating it from other taxa in his 1948 publication. Nevertheless, he did not do anything to rectify the situation, and Macruroryzomys remains a nomen nudum. Hershkovitz rejected any relationship between O. hammondi and Nectomys or O. aphrastus and instead argued that O. hammondi was closely similar to Megalomys and may be close to the ancestor of Megalomys. In 1982, Steadman and Ray mentioned the animal in passing under the name Macruroryzomys hammondi and reaffirmed its relationship to Megalomys. In the 2005 third edition of Mammal Species of the World
Mammal Species of the World
Mammal Species of the World, now in its 3rd edition, is a standard reference work in zoology giving descriptions and bibliographic data for the known species of mammals.An updated Third Edition of Mammal Species of the World was published late in 2005:...
, Guy Musser
Guy Musser
Guy Graham Musser is an American zoologist. His main research field is the subfamily Murinae, in which he has described many new species.Musser was born in Salt Lake City, Utah...
and Michael Carleton listed O. hammondi as an Oryzomys of obscure affinities, but suggested that it may be related to Megalomys.
Classification in Mindomys
In 2006, Marcelo Weksler published a large-scale cladisticCladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analysis of Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
("rice rats"), the group (tribe) to which hammondi and the related species mentioned above belong. He used both morphological and molecular characters, but had only morphological data for Oryzomys hammondi. The placement of the species in his results was unstable; some trees
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
placed it close to the tree rice rats, Oecomys
Oecomys
Oecomys is a genus of rodent within the tribe Oryzomyini of family Cricetidae. It contains about 17 species, which live in trees and are distributed across forested parts of South America, extending into Panama and Trinidad.-Literature cited:...
, within clade B and others placed it as an isolated lineage, basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
to all other Oryzomyini.
Traits of O. hammondi that supported the latter placement include: a relatively short palate that does not extend behind the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry bones; simple posterolateral palatal pits; absence of a capsular process
Capsular process
In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial side of the mandible as a raising in the bone...
(a raising of the bone of the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, 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). In these characters, O. hammondi differs from many or most Oryzomyini and is similar to some species outside Oryzomyini, but all traits of O. hammondi are present in at least one other member of the tribe. Traits shared by O. hammondi and Oecomys included: tail with the same coloration above and below (unicolored); parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
s extending to the sides of the skull; narrow zygomatic plate, without a zygomatic notch; posteroloph present on upper third molar; mesoflexus (a valley in the molar crown in front of the mesoloph crest) on upper second molar not divided in two.
In Weksler's analysis, species placed in Oryzomys did not form a coherent (monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
) group, but instead were found at various positions across the oryzomyine tree, and he suggested that most of these species, including O. hammondi, should be placed in new genera. Later in 2006, Weksler and others described ten new genera for species formerly placed in Oryzomys, including Mindomys for hammondi. Noting its "enigmatic distribution" and uncertain but perhaps basal position within Oryzomyini, they labeled the species an "extraordinary rat" worthy of continued inquiry. The generic name
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
refers to Mindo, the type locality of M. hammondi.
Mindomys is now one of about 28 genera in the tribe Oryzomyini, which includes well over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
and some of the Antilles
Antilles
The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...
. Oryzomyini is one of several tribes recognized within the subfamily Sigmodontinae
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
, other members of which include vole
Vole
A vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars . There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
s, lemming
Lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...
s, hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s, and deermice
Peromyscus
The genus Peromyscus contains the animal species commonly referred to as deer mice. This is a genus of New World mouse only distantly related to the common house mouse and laboratory mouse, Mus musculus...
, all mainly from Eurasia and North America.
Description
Mindomys hammondi is a large rice rat; all other rats within its range are smaller. The fur is relatively short and woolly and is buffy with a grayish tone above and much paler—yellow or white—below, with the bases of the hairs grey. It has a long snout and small, dark ears that appear hairless. The vibrissaeVibrissae
Vibrissae , or whiskers, are specialized hairs usually employed for tactile sensation. The term may also refer to the thick hairs found inside human nostrils, but these have no sensorial function and only operate as an airborne particulate barrier...
(whiskers) are long. The very long tail is dark both above and below and has rectangular scales. The hindfeet are broad, with long, narrow digits. They have poorly developed ungual tuft
Ungual tuft
In mammals, ungual tufts are tufts of hairs at the base of claws of the fore- and hindfeet. Their presence has been used as a character in cladistic studies of Cricetidae....
s, patches of hair between the digits and along the plantar margins. The squamae
Squamae
In some rodents, squamae are small tubercles resembling scales on the sole of the hindfeet. Among oryzomyine rodents, their development is variable; most have well-developed squamae, but in others they are indistinct or entirely absent. Delomys sublineatus and Peromyscus maniculatus also have...
, small structures resembling scales that cover the soles of the hindfeet in many oryzomyines, are indistinct. The fifth digit reaches to about half the length of the second phalange of the fourth. As in most oryzomyines, females have eight mammae. In specimens with published measurements, head and body length is 173 to 203 mm (6.8 to 8.0 in), tail length is 251 mm (9.9 in), hindfoot length is 41 to 42 mm (1.6 to 1.7 in), ear length is 18 mm (0.71 in), and greatest length of skull is 39.4 to 43.9 mm (1.55 to 1.73 in).
Skull
In the skullSkull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
, the rostrum (front part) is large and robust. The nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s are short, not extending further back than the lacrimals
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
, and the premaxillaries extend about as far back as the nasals. The zygomatic plate is narrow and lacks a zygomatic notch, an extension of the plate at the front. The plate's back margin is level with the front of the first upper molar. The narrowest part of the interorbital region
Interorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups....
, located between the eyes, is to the front and its margins exhibit strong beading. Various crests develop on the long braincase, especially in old animals. The parietal bones form part of the roof of the braincase and, unlike in some other rice rats, also extend to the sides of the braincase.
The incisive foramina
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
, perforations of the palate between the incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s and the molars, are short, not extending between the molars. The condition of the posterolateral palatal pits is variable, with some individuals having small pits and others having larger pits that may be recessed into a fossa (depression). The palate is moderately long, extending beyond the molars but not beyond the posterior margins of the maxillary bone. In most specimens, the roof of the mesopterygoid fossa, the gap behind the back of the palate, is not perforated by sphenopalatine vacuities
Sphenopalatine vacuities
In rodents, sphenopalatine vacuities are perforations of the roof of the mesopterygoid fossa, the open space behind the palate, in between the parapterygoid fossae. They may perforate the presphenoid or basisphenoid bone...
and thus it is fully ossified; if present, these vacuities are small. Mindomys lacks an alisphenoid strut
Alisphenoid strut
In some rodents, the alisphenoid strut is an extension of the alisphenoid bone that separates two foramina in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius...
; in some other oryzomyines, this extension of the alisphenoid bone separates two openings (foramina
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
) in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. There are no openings in the mastoid bone. The squamosal bone
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
, a defining character of oryzomyines.
In the mandible, the mental foramen
Mental foramen
The mental foramen is one of two holes located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals.- Variations :...
, an opening in the mandible just before the first molar, opens to the outside, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, join at a point below the first molar and do not extend forward beyond that point. There is no capsular process of the lower incisor, a trait Mindomys shares with only a few other oryzomyines.
Molars
The molarsMolar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
are bunodont (with the cusps higher than the connecting crests) and brachydont
Brachydont
Brachydont is a type of dentition characterized by low-crowned teeth, as opposed to high-crowned, hypsodont teeth. Human teeth are brachydont.-External links:*http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/tooth_diversity.html...
(low-crowned). On the upper first and second molar, the outer and inner valleys between the cusps and crests interpenetrate. Many accessory crests are present, including the mesolophs and mesolophids. The anterocone and anteroconid, the front cusps on the upper and lower first molar, are not divided into smaller outer and inner cusps. Unlike in Nectomys, Oryzomys, and Megalomys, the first upper and lower molars usually lack accessory roots, so that each of the three upper molars has two roots on the outer side and one on the inner side and each of the lower molars has one root at the front and one at the back.
Distribution and ecology
A rare species, Mindomys hammondi is known only from Ecuador. Between 1913 and 1980, eight specimens have been collected at Mindo, a "tiny agricultural community" at 1264 m (4150 ft) elevation in Pichincha ProvincePichincha Province
Pichincha is a province of Ecuador located in the northern sierra region; its capital and largest city is Quito. It is bordered by Imbabura & Esmeraldas to the north, Cotopaxi & Santo Domingo de los Tsáchilas to the south, Napo & Sucumbíos to the east, and Esmeraldas & Santo Domingo de los...
, 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 Amazonian lowlands of Napo Province
Napo Province
Napo is a province in Ecuador. Its capital is Tena. The province contains the Napo River. The province is low developed without much industrial presence. The thick rainforest is home to many natives that remain isolated by preference, descendents of those who fled the Spanish invasion in the Andes,...
, around 300 to 500 m (1000 to 1600 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. Furthermore, other collectors working in the same area in Napo have failed to find Mindomys, and the date the specimen was reportedly collected does not accord with the dates reported for the visit of the Olallas to Concepción, rendering its provenance dubious. There are two other locations named "Concepción" in northwestern Ecuador, and Diego Tirira suggested in 2007 that the specimen may instead be from one of these. Another specimen is known from Chaco, Imbabura Province
Imbabura Province
Imbabura is a province in Ecuador. The capital is Ibarra. The people of the province speak Spanish and the Imbaburan Quechua language.Imbabura Volcano is located in the province. Best reached from the town of La Esperanza, the 4,609-meter-high mountain can be climbed in a single day.- Cantons...
, at an altitude of 630 m (2070 ft).
Citing unpublished work by Tirira and Percequillo, the 2009 IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
reports that Mindomys is known from eleven specimens collected at four localities in northwestern Ecuador, and that its altitudinal range extends from 1200 to 2700 m (3900 to 8900 ft) above sea level, but does not give details. The species occurs in moist, montane forest on the foothills of the western Andes.
Almost nothing is known of the biology of Mindomys. In 1999, Eisenberg and Redford suggested that the species may live in trees; in 2007, Tirira agreed, citing the animal's broad feet. Tirira also suggested that it is nocturnal (active during the night) and solitary and eats fruits, seeds, and insects. According to the 2009 IUCN Red List, it lives on the ground and "apparently has some affinity with water".
Conservation status
The IUCN Red List lists Mindomys hammondi as "endangered" in view of its small known distribution and a continuing decline in the extent and quality of its habitat. Up to 40% of its habitat may already have been destroyed, and the species was last recorded in 1980. It is not known to occur in any protected areaProtected area
Protected areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the enabling laws of each country or the regulations of the international...
s, but has been recorded close to the protected forest of Mindo-Nambillo. It prefers well-conserved primary forest.
Literature cited
- Eisenberg, J.F. and Redford, K.H. 1999. Mammals of the Neotropics. Volume 3, The central Neotropics: Ecuador, Peru, Bolivia, Brazil. University of Chicago PressUniversity of Chicago PressThe University of Chicago Press is the largest university press in the United States. It is operated by the University of Chicago and publishes a wide variety of academic titles, including The Chicago Manual of Style, dozens of academic journals, including Critical Inquiry, and a wide array of...
, 624 pp. ISBN 978-0-226-19542-1 - Ellerman, J.R. 1941. The families and genera of living rodents. Vol. 2. Family Muridae. London: British Museum of Natural History, 690 pp.
- Hershkovitz, P. 1944. A systematic review of the Neotropical water rats of the genus Nectomys. Miscellaneous Publications of the Museum of Zoology, University of Michigan 58:1–88.
- Hershkovitz, P. 1948. Mammals of northern Colombia. Preliminary report No. 3: Water rats (genus Nectomys), with supplemental notes on related forms. Proceedings of the United States National Museum 98:49–56.
- Hershkovitz, P. 1970. Supplementary notes on Neotropical Oryzomys dimidiatus and Oryzomys hammondi (Cricetinae) (subscription required). Journal of Mammalogy 51(4):789–794.
- McCain, C.M., Timm, R.M. and Weksler, M. 2007. Redescription of the enigmatic long-tailed rat Sigmodontomys aphrastus (Cricetidae: Sigmodontinae) with comments on taxonomy and natural history (subscription required). Proceedings of the Biological Society of Washington 120:117–136.
- Musser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.). Mammal Species of the World: a taxonomic and geographic reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
- Percequillo, A.R., Weksler, M. and Costa, L.P. 2011. A new genus and species of rodent from the Brazilian Atlantic Forest (Rodentia: Cricetidae: Sigmodontinae: Oryzomyini), with comments on oryzomyine biogeography (subscription required). Zoological Journal of the Linnean Society 161(2):357–390.
- Ray, C.E. 1962. The Oryzomyine Rodents of the Antillean Subregion. Doctor of Philosophy thesis, Harvard University, 211 pp.
- Steadman, D.W. and Ray, C.E. 1982. The relationships of Megaoryzomys curioi, an extinct cricetine rodent (Muroidea: Muridae) from the Galápagos Islands, Ecuador. Smithsonian Contributions to Paleobiology 51:1–23.
- Thomas, O. 1913. New mammals from South America. Annals and Magazine of Natural History (8)12:566–574.
- Tirira, D. 2007. Guia de campo de los mamíferos del Ecuador. Quito: Ediciones Murciélago Blanco, publicación especial sobre los mamíferos del Ecuador 6, 576 pp. (in Spanish). ISBN 9978-44-651-6
- Tirira, D., Boada, C. and Weksler, M. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on February 21, 2010.
- Weksler, M. 2006. Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data. Bulletin of the American Museum of Natural History 296:1–149.
- Weksler, M., Percequillo, A.R. and Voss, R.S. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.