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Tympanoctomys barrerae

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Title: Tympanoctomys barrerae  
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Language: English
Subject: Ploidy, List of organisms by chromosome count, Golden vizcacha rat
Publisher: World Heritage Encyclopedia

Tympanoctomys barrerae

Plains viscacha rat
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Octodontidae
Genus: Tympanoctomys
Yepes, 1942
Species: T. barrerae
Binomial name
Tympanoctomys barrerae
(B. Lawrence, 1941)[2]

The plains viscacha rat or red vizcacha rat (Tympanoctomys barrerae) is a species of rodent in the family Octodontidae. The rodent is not a rat, but related to guinea pigs and chinchillas. It is monotypic within the genus Tympanoctomys.[3] It is endemic to central western Argentina, where it has a fragmented range.[1] Its natural habitat is desert scrubland, dunes and salt flats, where it eats halophyte plants.[1] It is a solitary, nocturnal rodent that constructs large mounds with complex burrows.[1][4]

This species of rodent was thought to be unusual because it is tetraploid (4x = 2n = 102). Scientists thought that this species may have arisen when an ancestor (very possibly the mountain vizcacha rat, Octomys mimax, chromosome count 2x = 2n = 56) doubled its chromosome number, presumably by errors in mitosis or meiosis within the animal's reproductive organs.[5]

However, careful analysis using chromosome paints shows that there are only two copies of each chromosome in T. barrerae not the four expected if it were truly a tetraploid.[6] Its "new" diploid [2n] number is 112 and so its cells are roughly twice normal size by virtue of having twice as many chromosomes instead of twice as many sets of chromosomes. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 2n = 4x = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.

The species is threatened by destruction of its fragmented and restricted habitat.[1]


  • Mares, M. A.; Braun, J. K.; Barquez, R. M.; Díaz, M. M. 2000. Two new genera and species of halophytic desert mammals from isolated salt flats in Argentina. Occasional Papers, Museum of Texas Tech University 203:i+1-27.

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