Hypogeomys australis
Encyclopedia
Hypogeomys australis is an extinct rodent
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
(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.
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
. In 1946, Charles Lamberton illustrated another femur
(upper leg bone) of H. australis; the origin and current whereabouts of this specimen are unknown. In 1996, Steven Goodman
and Daniel Rakotondravony reviewed the distribution of Hypogeomys and confirmed that H. australis is a distinct species. H. australis and H. antimena are classified together within the exclusively Madagascan subfamily Nesomyinae
of the family Nesomyidae
, which includes various African rodents.
with more distinct crests and lobes. 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.
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
. A bone from Andrahomana has been radiocarbon dated
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. 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
; both of these photosynthesis
-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
from northwestern Madagascar). In general, few small animals went extinct on Madagascar, except for these rodents, two species of Plesiorycteropus, and the shrew tenrec Microgale macpheei
; in contrast, large animals such as subfossil lemur
s, the carnivore Cryptoprocta spelea
, Malagasy hippopotamus
es, Dipsochelys
tortoises, and Aepyornis
and Mullerornis
birds all went extinct around the time that humans arrived.
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....
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
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(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
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
based on radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...
. 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 GrandidierGuillaume Grandidier
Guillaume Grandidier 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 Madagascar...
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....
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
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 recent studies have found little evidence to link it to aardvarks or any other order of...
. In 1946, Charles Lamberton illustrated another femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(upper leg bone) of H. australis; the origin and current whereabouts of this specimen are unknown. In 1996, Steven Goodman
Steven Goodman
Steven Goodman is an American Conservation Biologist, and field biologist on staff in the Department of Zoology at the Field Museum of Natural History....
and Daniel Rakotondravony reviewed the distribution of Hypogeomys and confirmed that H. australis is a distinct species. H. australis and H. antimena are classified together within 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
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 as more robust, with more prominent muscle scars on the long bones and with longer 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"....
with more distinct crests and lobes. 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 AntsirabeAntsirabe
Antsirabe is the third largest city in Madagascar and has a population of approximately 183,000. It's the capital of the Vakinankaratra region...
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
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"...
. A bone from Andrahomana has been radiocarbon dated
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...
to about 4440 BP
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
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. 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
C4 carbon fixation
C4 carbon fixation is one of three biochemical mechanisms, along with and CAM photosynthesis, used in carbon fixation. It is named for the 4-carbon molecule present in the first product of carbon fixation in these plants, in contrast to the 3-carbon molecule products in plants. fixation is an...
and crassulacean acid metabolism
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. The stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide...
; both of these photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
-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
Brachytarsomys 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...
and Nesomys narindaensis
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 in the genus Nesomys together with three smaller living...
from northwestern Madagascar). In general, few small animals went extinct on Madagascar, except for these rodents, two species of Plesiorycteropus, and the shrew tenrec Microgale macpheei
Microgale macpheei
Microgale macpheei is an extinct shrew tenrec from southeastern Madagascar. It is known only from two partial skulls found in Andrahomana cave, which radiocarbon dating of associated rodent remains suggests are about 2000 years old. It is the only known recently extinct tenrec...
; in contrast, large animals such as subfossil lemur
Subfossil lemur
Subfossil lemurs are lemurs from Madagascar that are represented by recent remains dating from nearly 26,000 years ago to approximately 560 years ago. They include both living and extinct species, although the term more frequently refers to the extinct giant lemurs...
s, the carnivore Cryptoprocta spelea
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 1902, and in 1935 was recognized as a separate species...
, Malagasy hippopotamus
Malagasy Hippopotamus
Several species of Malagasy Hippopotamus lived on the island of Madagascar but are now believed to be extinct. The animals were very similar to the extant Hippopotamus and Pygmy Hippopotamus...
es, Dipsochelys
Dipsochelys
Dipsochelys is a genus of giant tortoise restricted to Madagascar and the Seychelles islands, containing six species:* †Dipsochelys abrupta Grandidier 1868 - Madagascar,...
tortoises, and Aepyornis
Aepyornis
Aepyornis is a genus of aepyornithid, one of two genera of ratite birds endemic to Madagascar known as elephant birds. This animal was the world's largest bird until its extinction, about 1000 years ago.-Description:...
and Mullerornis
Mullerornis
Mullerornis is the smaller of the two genera of extinct elephant birds of Madagascar . Species include Mullerornis agilis Milne-Edwards and A. Grandidier, 1894, and M. grandis Lamberton, 1934...
birds all went extinct around the time that humans arrived.
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 lHypogeomys 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. ISBN 978-0-8018-8221-0
- 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. ISBN 978-0-19-953509-5