''Hypogeomys australis'' is an extinct

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

from central and southeastern Madagascar. First described in 1903, it is larger than its close relative, the living '' Hypogeomys antimena'', which occurs further west, but otherwise similar. Average length of the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

(upper leg bone) is 72.1 mm, compared to 63.8 mm in ''H. antimena''. One of the few extinct rodents of Madagascar, it survived to at least around 1536 BP based on radiocarbon dating. Little is known of its ecology, but it may have lived in burrows like its living relative and eaten some arid-adapted plants.

Taxonomy

''Hypogeomys australis'' was described in 1903 by

Guillaume Grandidier Guillaume Grandidier (1 July 1873 – 13 September 1957) was a French geographer, ethnologist, zoologist who studied the island of Madagascar. He was the son of the wealthy industrialist Alfred Grandidier also a zoologist and expert on Madagasca ...

from subfossil material collected in the cave of Andrahomana in southeastern Madagascar. The ''Hypogeomys'' material was similar to the living '' Hypogeomys antimena'', but distinct enough for Grandidier to recognize it as a separate species, different in size and some morphological details. Grandidier described another subfossil ''Hypogeomys'' species in 1912, ''H. boulei'', but the material that species was based on was later identified as the enigmatic mammal ''

Plesiorycteropus ''Plesiorycteropus'', also known as the bibymalagasy or Malagasy aardvark, is a recently extinct eutherian mammalian genus from Madagascar. Upon its description in 1895, it was classified with the aardvark, but more recent molecular evidence ins ...

''. In 1946,

Charles Lamberton Charles Lamberton (23 April 18768 October 1960) was a French paleontologist who lived and studied on the island of Madagascar between 1911 and 1948 and specialized in the recently extinct subfossil lemurs. He made significant contributions towa ...

illustrated another

(upper leg bone) of ''H. australis''; the origin and current whereabouts of this specimen are unknown.Goodman and Rakotondravony, 1996, p. 285 In 1996, Steven Goodman and Daniel Rakotondravony reviewed the distribution of ''Hypogeomys'' and confirmed that ''H. australis'' is a distinct species.Goodman and Rakotondravony, 1996, p. 286 ''H. australis'' and ''H. antimena'' are classified together within the exclusively Madagascan subfamily

Nesomyinae The Malagasy rodents 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 ge ...

of the family

Nesomyidae The Nesomyidae are 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. Included in this family are Malagasy rodents, ...

, which includes various African rodents.

Description

''Hypogeomys australis'' was generally similar to ''H. antimena'', the largest living rodent of Madagascar, but even larger, with little if any overlap in measurements. Grandidier described the extinct

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

as more robust, with more prominent muscle scars on the long bones and with longer

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

with more distinct crests and lobes.Grandidier, 1903, p. 14 The length of the first lower molar is 5.2 to 6.4 mm, averaging 5.7 mm, in ten ''H. australis'' and 3.9 to 5.5 mm, averaging 4.8 mm, in twenty-four ''H. antimena''. The width of the femur at the proximal (near) end is 18.6 to 21.5 mm, averaging 19.9 mm, in thirteen ''H. australis'' and 16.8 to 18.5 mm, averaging 17.5 mm, in nine ''H. antimena''. In ten ''H. australis'', total length of the femur is 69.9 to 75.1 mm, averaging 72.1 mm, compared to 59.7 to 69.9 mm, averaging 63.8 mm in nine ''H. antimena''.

Distribution and ecology

Remains attributed to ''Hypogeomys australis'' are known from Andrahomana in southeastern Madagascar and Antsirabe in central Madagascar, suggesting a broad former distribution. Its range is not known to overlap that of ''H. antimena'', which has undergone a dramatic reduction during the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

.Goodman and Rakotondravony, 1996, p. 290 A bone from Andrahomana has been

radiocarbon dated Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was dev ...

to about 4440 BP and another to 1536 BP. Although almost nothing is known of the ecology of ''H. australis'', Goodman and Rakotondravony presumed that it was similar to its living relative in living in burrows in areas with loose soils.Goodman and Rakotondravony, 1996, p. 287 ''H. australis'' shows relatively high content of carbon-13 isotope, likely because it ate some plants which were enriched in carbon-13 through C₄ carbon fixation and

crassulacean acid metabolism Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. ...

; both of these

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

-related processes occur most frequently in plants adapted to dry environments. ''Hypogeomys australis'' is one of only three extinct rodents known from Madagascar (the others are '' Brachytarsomys mahajambaensis'' and ''

Nesomys narindaensis ''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 i ...

'' from northwestern Madagascar). In general, few small animals became extinct on Madagascar, except for these rodents, two species of ''Plesiorycteropus'', and the shrew tenrec '' Microgale macpheei''; in contrast, large animals such as subfossil lemurs, the carnivore ''

Cryptoprocta spelea ''Cryptoprocta spelea'', also known as the giant fossa, is an extinct species of carnivore from Madagascar in the family Eupleridae which is most closely related to the mongooses and includes all Malagasy carnivorans. It was first described in 19 ...

'', Malagasy hippopotamuses, ''

Dipsochelys ''Aldabrachelys'' is the recognised genus for the Seychelles and Madagascan radiations of giant tortoises, including the Aldabra giant tortoise (''Aldabrachelys gigantea''). Naming This name is problematic in that the type specimen is actually r ...

'' tortoises, and ''

Aepyornis ''Aepyornis'' is a genus of aepyornithid, one of three genera of ratite birds endemic to Madagascar until their extinction sometime around 1000 CE. The species ''A. maximus'' weighed up to , and until recently was regarded as the largest known ...

'' and ''

Mullerornis ''Mullerornis'' is a genus of extinct elephant birds (Aepyornithidae) of Madagascar. Description ''Mullerornis'' is smaller than the more well-known '' Aepyornis''. A bone possibly belonging to ''Mullerornis'' has been radiocarbon dated to abo ...

'' birds all became extinct around the time that humans arrived.Turvey, 2009, pp. 32–33

References

Literature cited

*Burney, D.A., Burney, L.P., Godfrey, L.R., Jungers, W.L., Goodman, S.M., Wright, H.T. and Jull, A.J.T. 2004
A chronology for late prehistoric Madagascar
(subscription required). Journal of Human Evolution 47:25–63. *Crowley, B.E., Godfrey, L.R. and Irwin, M.T. 2010
A glance to the past: subfossils, stable isotopes, seed dispersal, and lemur species loss in Southern Madagascar
(subscription required). American Journal of Primatology 71:1–13. *Goodman, S.M. and Rakotondravony, D. 1996
The Holocene distribution of ''Hypogeomys'' (Rodentia: Muridae: Nesomyinae) on Madagascar
Biogéographie de Madagascar 1996:283–293. *Grandidier, G. 1903
Description de l''Hypogeomys australis'', nouvelle espèce de Rongeur sub-fossile de Madagascar
Bulletin du Muséum national d'histoire naturelle 9:13–15 (in French). *MacPhee, R.D.E. 1994
Morphology, adaptations, and relationships of ''Plesiorycteropus'', and a diagnosis of a new order of eutherian mammals
Bulletin of the American Museum of Natural History 220:1–214. *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. *Sommer, S. 1996
Ecology and social structure of ''Hypogeomys antimena'', an endemic rodent of the dry deciduous forest in western Madagascar
Biogéographie de Madagascar 1996:295–302. *Turvey, S.T. 2009
Holocene Extinctions
Oxford University Press US, 359 pp. {{Taxonbar, from=Q16991961 Extinct rodents Hypogeomys Holocene extinctions Extinct animals of Madagascar Fossil taxa described in 1903