Nesomys narindaensis
Encyclopedia
Nesomys narindaensis is an extinct rodent
that lived in northwestern Madagascar
. It is known from subfossil
skull bones and isolated molars
found in several sites during field work that started in 2001. First described in 2010, it is placed in the genus Nesomys
together with three smaller living species, which may differ in some details of molar morphology. The presence of N. narindaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.
. The specific name, narindaensis, where one of the sites where the species has been found is located. It is placed in the genus Nesomys
, together with three smaller living species, N. audeberti, N. lambertoni, and N. rufus. Nesomys is classified in the exclusively Madagascan subfamily Nesomyinae
of the family Nesomyidae
, which includes various African rodents.
(lower jaw) with the first two molars
(m1 and m2), and four isolated molars (one first upper molar, M1, one third upper molar, M3, and two m2). It is larger than each of the three living species, and the known material additionally differs from those in a few details that may not hold in larger samples. Total skull length is 61.3 mm, longer than in the largest living species, N. lambertoni (50.3–53.8 mm). The width of the palate
between the M1 is 8.7 mm (7.2–7.9 mm in N. lambertoni) and the length of the upper toothrow is 9.04 and 9.16 mm on the two sides of the skull (7.2–7.9 mm in N. lambertoni).
M1 is flat-crowned. The anteroloph, a crest at the front of the tooth, lacks a smaller accessory spur that is present in N. rufus. The paracone
, one of the main cusps, is quite small; this cusp is more prominent in N. rufus. The mesoloph, a crest on the middle of the tooth, is distinct but short and located further to the back than in N. rufus. M2 has a longer mesoloph. M3 is largely flat-crowned, but the paracone is a bit more prominent than the rest. The valley between the cusps at the front is deeper than the valleys at the back. Each of the upper molars has three roots.
The m1 is long and narrow. The anteroconid, the cusp at the front of the tooth, is oriented perpendicularly to the main axis of the tooth and on the lingual (inner) side is separated from the metaconid cusp. The protoconid, another cusp on the labial (outer) side, is connected at its back to a longitudinal crest, which in turn anchors the transverse mesolophid crest, and then joins the hypoconid labial cusp. In front of the hypoconid, an ectostylid (a smaller cuspule) is present. The entoconid cusp, located lingually, is relatively high and is separated from the mesolophid before it by a deep valley. Another crest, the posterolophid, is present behind the hypoconid. At the front of the m2, crests known as the anterolophid and anterolabial cingulum are present before the protoconid and the metaconid. As on the m1, a transverse mesolophid and an ectostylid are present. The hypoconid and the entoconid are present, as is the posterolophid behind them. Within the posterolophid, there is a small valley that is absent in N. rufus. Both m1 and m2 have two roots; m3 is unknown.
(126,000 to 10,000 years ago) and Holocene
(less than 10,000 years ago) in age. Nesomys is a rare element of the rodent fauna, which is dominated by multiple species of Eliurus
and Macrotarsomys
. Modern Nesomys live on the ground in eastern (N. audeberti and N. rufus) and western (N. lambertoni) Madagascar. The only surviving western species, N. lambertoni, is restricted to a relict humid karst
area; the presence of N. narindaensis and Brachyuromys mahajambaensis suggests that the past environment in northwestern Madagascar was also more humid. Subfossil
remains of Nesomys have been recorded from some other localities in northwestern Madagascar, but these have not been described.
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....
that lived in northwestern Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. It is known from subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
skull bones and isolated molars
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"....
found in several sites during field work that started in 2001. First described in 2010, it is placed in the genus Nesomys
Nesomys
Nesomys is a genus of rodent in the family Nesomyidae. It is found only on Madagascar, and contains the following species:* White-bellied Nesomys * Western Nesomys * Nesomys narindaensis †...
together with three smaller living species, which may differ in some details of molar morphology. The presence of N. narindaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.
Taxonomy
Remains of Nesomys narindaensis were found during fieldwork in northwestern Madagascar that started in 2001. The species was described in a 2010 paper by Pierre Mein and colleagues, together with another extinct rodent, Brachytarsomys mahajambaensisBrachytarsomys mahajambaensis
Brachytarsomys mahajambaensis is an extinct rodent from northwestern Madagascar. It is known from nine isolated molars found in several sites during field work that started in 2001. First described in 2010, it is placed in the genus Brachytarsomys together with two larger living species, which may...
. The specific name, narindaensis, where one of the sites where the species has been found is located. It is placed in the genus Nesomys
Nesomys
Nesomys is a genus of rodent in the family Nesomyidae. It is found only on Madagascar, and contains the following species:* White-bellied Nesomys * Western Nesomys * Nesomys narindaensis †...
, together with three smaller living species, N. audeberti, N. lambertoni, and N. rufus. Nesomys is classified in the exclusively Madagascan subfamily Nesomyinae
Nesomyinae
The Malagasy rats and mice are the sole members of the subfamily Nesomyinae. These animals are the only native rodents of Madagascar, come in many shapes and sizes, and occupy a wide variety of ecological niches. There are nesomyines that resemble gerbils, rats, mice, voles, and even rabbits...
of the family Nesomyidae
Nesomyidae
Nesomyidae is a family of African rodents in the large and complex superfamily Muroidea. It includes several subfamilies, all of which are native to either continental Africa or to Madagascar...
, which includes various African rodents.
Description
Nesomys narindaensis is known from a damaged skull, missing part of the back, a mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(lower jaw) with the first two molars
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"....
(m1 and m2), and four isolated molars (one first upper molar, M1, one third upper molar, M3, and two m2). It is larger than each of the three living species, and the known material additionally differs from those in a few details that may not hold in larger samples. Total skull length is 61.3 mm, longer than in the largest living species, N. lambertoni (50.3–53.8 mm). The width 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...
between the M1 is 8.7 mm (7.2–7.9 mm in N. lambertoni) and the length of the upper toothrow is 9.04 and 9.16 mm on the two sides of the skull (7.2–7.9 mm in N. lambertoni).
M1 is flat-crowned. The anteroloph, a crest at the front of the tooth, lacks a smaller accessory spur that is present in N. rufus. The paracone
Paracone
An atmospheric reentry or spaceflight mission abort concept using an inflatable cone.A notable feature of the paracone concept is that it facilitates an abort throughout the entire flight profile....
, one of the main cusps, is quite small; this cusp is more prominent in N. rufus. The mesoloph, a crest on the middle of the tooth, is distinct but short and located further to the back than in N. rufus. M2 has a longer mesoloph. M3 is largely flat-crowned, but the paracone is a bit more prominent than the rest. The valley between the cusps at the front is deeper than the valleys at the back. Each of the upper molars has three roots.
The m1 is long and narrow. The anteroconid, the cusp at the front of the tooth, is oriented perpendicularly to the main axis of the tooth and on the lingual (inner) side is separated from the metaconid cusp. The protoconid, another cusp on the labial (outer) side, is connected at its back to a longitudinal crest, which in turn anchors the transverse mesolophid crest, and then joins the hypoconid labial cusp. In front of the hypoconid, an ectostylid (a smaller cuspule) is present. The entoconid cusp, located lingually, is relatively high and is separated from the mesolophid before it by a deep valley. Another crest, the posterolophid, is present behind the hypoconid. At the front of the m2, crests known as the anterolophid and anterolabial cingulum are present before the protoconid and the metaconid. As on the m1, a transverse mesolophid and an ectostylid are present. The hypoconid and the entoconid are present, as is the posterolophid behind them. Within the posterolophid, there is a small valley that is absent in N. rufus. Both m1 and m2 have two roots; m3 is unknown.
Distribution and ecology
Remains of Nesomys narindaensis have been found at the sites of Antsingiavo, Ambongonambakoa, and Ambatomainty in northwestern Madagascar, which are late PleistocenePleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
(126,000 to 10,000 years ago) and Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
(less than 10,000 years ago) in age. Nesomys is a rare element of the rodent fauna, which is dominated by multiple species of Eliurus
Eliurus
Eliurus is a genus of rodent in the family Nesomyidae.It contains the following species:* Tsingy Tufted-tailed Rat * Ankarana Special Reserve Tufted-tailed Rat...
and Macrotarsomys
Macrotarsomys
Macrotarsomys is a genus of rodent in the family Nesomyidae.It contains the following species:Genus Macrotarsomys - Big-footed mice*Bastard Big-Footed Mouse, Macrotarsomys bastardi Milne-Edwards and G. Grandidier, 1898...
. Modern Nesomys live on the ground in eastern (N. audeberti and N. rufus) and western (N. lambertoni) Madagascar. The only surviving western species, N. lambertoni, is restricted to a relict humid karst
KARST
Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...
area; the presence of N. narindaensis and Brachyuromys mahajambaensis suggests that the past environment in northwestern Madagascar was also more humid. Subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
remains of Nesomys have been recorded from some other localities in northwestern Madagascar, but these have not been described.
Literature cited
- Mein, P., Sénégas, F., Gommery, D., Ramanivoso, B., Randrianantenaina, H. and Kerloc'h, P. 2010. Nouvelles espèces subfossiles de rongeurs du Nord-Ouest de Madagascar (subscription required). Comptes Rendus Palevol 9(3):101–112 (in French, with abridged English version).
- 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