Oecomys sydandersoni
Encyclopedia
Oecomys sydandersoni is an arboreal species of rodent
in the genus Oecomys
. It lives in forest patches in a small area in eastern Bolivia. It is a medium-sized species, weighing about 45 g (1.6 oz), with mostly grayish and brownish fur and short and broad hindfeet with well-developed pads.
First collected in 1964, it was formally described in 2009. The species may be most closely related to O. concolor and O. mamorae, which are distributed further north and south in South America. Among other characters, the three share a particular arrangement of the arteries
of the head. Virtually nothing is known of its biology.
expedition led by Sydney Anderson collected the first three specimens of Oecomys sydandersoni in 1964 and 1965. The material was mentioned in passing in a report on the chigger
s of the region and tentatively identified as O. concolor in publications of the 1990s. During studies in the Noel Kempff Mercado National Park
(NKMNP) from 1997 to 2006, Smithsonian
zoologist Louise Emmons and coworkers obtained large series of Oecomys, including four species—Oecomys bicolor, Oecomys roberti, Oecomys trinitatis, and a fourth species they could not identify to species level. In 2009, Michael Carleton, Louise Emmons, and Guy Musser described the latter as a new species, Oecomys sydandersoni, referring to it the specimens collected in the 1960s and previously identified as O. concolor. They named the new species after Sydney Anderson in honor of his work on the Bolivian mammal fauna, including the first collection of O. sydandersoni.
Its closest relatives may be O. concolor from northern Amazonia, including northwestern Brazil, southern Venezuela, and eastern Colombia, and O. mamorae from Bolivia, Paraguay, nearby Brazil, and possibly northeastern Argentina. The three share a particular configuration of the arteries
in the head known as the derived carotid arterial circulatory pattern, which is unique within the genus Oecomys, and a general similarity in other traits. However, O. sydandersoni differs from the other two in characters of the fur and in metric characters. Whether the three species are truly closely related needs to be determined using molecular data.
All three are part of the genus Oecomys
, which includes about fifteen species distributed in rainforest habitats in South America and into southern Central America. Oecomys is one of the genera of the tribe Oryzomyini
("rice rats"), a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels is classified in the subfamily Sigmodontinae
of family Cricetidae
, along with hundreds of other species of mainly small rodents.
s are black. Short hairs thinly cover the external ears, which are brown to gray-brown in color. The short and broad hindfeet are dirty white and show some characters that are typical of the genus, including well-developed pads and tufts of hair on the digits and a long fifth digit. The tail is slightly longer than the head and body on average, but relatively short for the genus. It is uniformly brown, but with a somewhat paler portion below near its base. Sparsely haired, the tail ends in a rudimentary pencil. There is no evidence for sexual dimorphism
.
The skull
shows a short front part (rostrum) and a broad interorbital region
(located between the eyes). The roof of the braincase is marked by supraorbital shelves. The incisive foramina
, which perforate the front part of the palate
, are very broad and extend between the first molar
s. The zygomatic plate
s, the flattened anterior portions of the zygomatic arch
es (cheekbones), are expansive and show well-developed notches at their front ends. The palate itself is flat and ends a little behind the third molars. The posterolateral palatal pits
, located near the third molars, are well developed. The mesopterygoid fossa, the opening behind the end of the palate, is rounded at the frond and broad. An extension of the alisphenoid bone known as the alisphenoid strut
is usually present, separating two foramina (openings), the foramen ovale accessorius and the masticatory-buccinator foramen. The roof of the tympanic cavity
, the tegmen tympani, is small.
The upper incisor
s are opisthodont, with the chewing edge located behind the vertical plane of the incisors. As is usual for the genus, the molars are brachyodont, low-crowned, and bunodont, with the cusps higher than the connecting crests, and accessory crests such as mesolophs are present. On the upper first molar, the frontmost cusp, the anterocone, is divided into two small cusps in young individuals, connected by a crest, but the two fuse with wear.
and Santa Cruz
in eastern Bolivia, including the Noel Kempff Mercado National Park
(NKMNP), where the type locality is located. All but a few specimens come from pockets of woodland in seasonally flooded grasslands, where it is the most frequently encountered rodent; the related oryzomyine Hylaeamys acritus
, the spiny rat
Proechimys longicaudatus, and the opossum Marmosa murina were found in the same habitat. It is absent in other, more contiguous forests and in other grasslands without large forest patches. Thus, O. sydandersoni is a narrow habitat specialist with a limited distribution. It joins several other species with restricted ranges found in the NKMNP, including Hylaeamys acritus, the akodontine
rodents Juscelinomys guaporensis and J. huanchae, and an opossum, Cryptonanus unduaviensis.
All specimens from the NKMNP were caught above the ground in vegetation, suggesting that the species is arboreal like the other members of its genus. The chigger Eutrombicula batatas
has been found on O. sydandersoni. Nothing else is known about ecology, behavior, diet, reproduction, or conservation status.
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 genus 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:...
. It lives in forest patches in a small area in eastern Bolivia. It is a medium-sized species, weighing about 45 g (1.6 oz), with mostly grayish and brownish fur and short and broad hindfeet with well-developed pads.
First collected in 1964, it was formally described in 2009. The species may be most closely related to O. concolor and O. mamorae, which are distributed further north and south in South America. Among other characters, the three share a particular arrangement of the arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
of the head. Virtually nothing is known of its biology.
Taxonomy
An American Museum of Natural HistoryAmerican Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
expedition led by Sydney Anderson collected the first three specimens of Oecomys sydandersoni in 1964 and 1965. The material was mentioned in passing in a report on the chigger
Chigger
A chigger or harvest mite is a mite in the family Trombiculidae that lives in North American forests and grasslands.Chigger may also refer to:...
s of the region and tentatively identified as O. concolor in publications of the 1990s. During studies in the Noel Kempff Mercado National Park
Noel Kempff Mercado National Park
Noel Kempff Mercado National Park is a national park in northeast Santa Cruz Department, Province of José Miguel de Velasco, Bolivia, on the border with Brazil.-Description:...
(NKMNP) from 1997 to 2006, Smithsonian
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
zoologist Louise Emmons and coworkers obtained large series of Oecomys, including four species—Oecomys bicolor, Oecomys roberti, Oecomys trinitatis, and a fourth species they could not identify to species level. In 2009, Michael Carleton, Louise Emmons, and Guy Musser described the latter as a new species, Oecomys sydandersoni, referring to it the specimens collected in the 1960s and previously identified as O. concolor. They named the new species after Sydney Anderson in honor of his work on the Bolivian mammal fauna, including the first collection of O. sydandersoni.
Its closest relatives may be O. concolor from northern Amazonia, including northwestern Brazil, southern Venezuela, and eastern Colombia, and O. mamorae from Bolivia, Paraguay, nearby Brazil, and possibly northeastern Argentina. The three share a particular configuration of the arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
in the head known as the derived carotid arterial circulatory pattern, which is unique within the genus Oecomys, and a general similarity in other traits. However, O. sydandersoni differs from the other two in characters of the fur and in metric characters. Whether the three species are truly closely related needs to be determined using molecular data.
All three are part of the genus 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:...
, which includes about fifteen species distributed in rainforest habitats in South America and into southern Central America. Oecomys is one of the genera 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...
("rice rats"), a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels is classified in 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...
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...
, along with hundreds of other species of mainly small rodents.
Description
Oecomys sydandersoni is medium-sized for its genus, being larger than, for example, O. bicolor, but smaller than O. concolor and O. mamorae. Its short, soft, and fine fur is bright ochraceous brown to pale tawny on the upperparts, changing moderately abruptly into the generally gray underparts. The fur on the chin, throat, and part of the belly is entirely white. The head is more grayish than the rest of the upperparts and the eyelidEyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
s are black. Short hairs thinly cover the external ears, which are brown to gray-brown in color. The short and broad hindfeet are dirty white and show some characters that are typical of the genus, including well-developed pads and tufts of hair on the digits and a long fifth digit. The tail is slightly longer than the head and body on average, but relatively short for the genus. It is uniformly brown, but with a somewhat paler portion below near its base. Sparsely haired, the tail ends in a rudimentary pencil. There is no evidence for sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
.
| Measurement | Range | Average |
|---|---|---|
| Head and body length | 109 to 166 mm (4.3 to 6.5 in) | 125.0 mm (4.92 in) |
| Tail length | 115 to 145 mm (4.5 to 5.7 in) | 132.8 mm (5.23 in) |
| Hindfoot length | 21 to 27 mm (0.83 to 1.1 in) | 24.1 mm (0.95 in) |
| Ear length | 15 to 19 mm (0.59 to 0.75 in) | 16.4 mm (0.65 in) |
| Mass | 30 to 57 g (1.1 to 2.0 oz) | 44.9 g (1.58 oz) |
The skull
Skull
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...
shows a short front part (rostrum) and a broad 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). The roof of the braincase is marked by supraorbital shelves. 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:...
, which perforate the front part 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...
, are very broad and extend between the first molar
Molar (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"....
s. 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...
s, the flattened anterior portions of the zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
es (cheekbones), are expansive and show well-developed notches at their front ends. The palate itself is flat and ends a little behind the third molars. The 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...
, located near the third molars, are well developed. The mesopterygoid fossa, the opening behind the end of the palate, is rounded at the frond and broad. An extension of the alisphenoid bone known as the 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...
is usually present, separating two foramina (openings), the foramen ovale accessorius and the masticatory-buccinator foramen. 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....
, the tegmen tympani, is small.
The upper incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s are opisthodont, with the chewing edge located behind the vertical plane of the incisors. As is usual for the genus, the molars are brachyodont, low-crowned, and bunodont, with the cusps higher than the connecting crests, and accessory crests such as mesolophs are present. On the upper first molar, the frontmost cusp, the anterocone, is divided into two small cusps in young individuals, connected by a crest, but the two fuse with wear.
Distribution and ecology
O. sydandersoni is known from the departments of BeniBeni Department
Beni, sometimes El Beni, is a northeastern department of Bolivia, in the lowlands region of the country. It is the second largest department in the country , covering 213,564 square kilometers , and it was created by supreme decree on November 18, 1842 during the administration of General José...
and Santa Cruz
Santa Cruz Department
Santa Cruz, with an area of 370,621 km², is the largest of the nine constituent departments of Bolivia. In the 2001 census, it reported a population of 2,029,471. The capital is the city of Santa Cruz de la Sierra. The state is one of the wealthiest states in Bolivia with huge reserves of...
in eastern Bolivia, including the Noel Kempff Mercado National Park
Noel Kempff Mercado National Park
Noel Kempff Mercado National Park is a national park in northeast Santa Cruz Department, Province of José Miguel de Velasco, Bolivia, on the border with Brazil.-Description:...
(NKMNP), where the type locality is located. All but a few specimens come from pockets of woodland in seasonally flooded grasslands, where it is the most frequently encountered rodent; the related oryzomyine Hylaeamys acritus
Hylaeamys acritus
Hylaeamys acritus, formerly Oryzomys acritus, is an oryzomyine rodent of the family Cricetidae. It is known only from northeastern Bolivia. It is terrestrial and is found in moist lowland semideciduous forest and savanna.-References:...
, the spiny rat
Spiny rat
The spiny rats are a group of hystricognath rodents in the family Echimyidae. They are distributed from central Central America through much of South America. They were also found in the West Indies until the 19th century...
Proechimys longicaudatus, and the opossum Marmosa murina were found in the same habitat. It is absent in other, more contiguous forests and in other grasslands without large forest patches. Thus, O. sydandersoni is a narrow habitat specialist with a limited distribution. It joins several other species with restricted ranges found in the NKMNP, including Hylaeamys acritus, the akodontine
Akodontini
Akodontini is the second most speciose tribe of the subfamily Sigmodontinae. It includes at least 106 living species in 19 genera and is distributed mainly in the southern half of South America, with only two genera extending into Guyana and Venezuela . It also includes genera previously placed in...
rodents Juscelinomys guaporensis and J. huanchae, and an opossum, Cryptonanus unduaviensis.
All specimens from the NKMNP were caught above the ground in vegetation, suggesting that the species is arboreal like the other members of its genus. The chigger Eutrombicula batatas
Eutrombicula batatas
Eutrombicula batatas is a species of chigger .Host species include:Didelphimorphia*Didelphis marsupialis in Venezuela*Lutreolina crassicaudata in Venezuela*Marmosa robinsoni in Venezuela...
has been found on O. sydandersoni. Nothing else is known about ecology, behavior, diet, reproduction, or conservation status.
Literature cited
- Anderson, S. 1997. Mammals of Bolivia, taxonomy and distribution. Bulletin of the American Museum of Natural History 231:1–652.
- Brennan, J.M. 1970. Chiggers from the Bolivian-Brazilian border (Acarina: Trombiculidae) (subscription required). Journal of Parasitology 56:807–812.
- Carleton, M.D., Emmons, L.H. and Musser, G.G. 2009. A new species of the rodent genus Oecomys (Cricetidae: Sigmodontinae: Oryzomyini) from eastern Bolivia, with emended definitions of O. concolor (Wagner) and O. mamorae (Thomas). American Museum Novitates 3661:1–32.
- 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
- 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.