The toros or brush-tailed rats, genus ''Isothrix'', are a group of spiny rats found in

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

, particularly in the Amazon Basin.Nowak, Ronald M. 1999. ''Walker's Mammals of the World'', 6th edition. Johns Hopkins University Press, 1936 pp.

Description

Toros look like large rats with soft fur on the body and long

guard hair Guard hair or overhair is the outer layer of hair of most mammals, which overlay the fur. Guard hairs are long and coarse and protect the rest of the pelage (fur) from abrasion and frequently from moisture. They are visible on the surface of the fu ...

s on the scaly tail.Emmons, L.H. 2005. A Revision of the Genera of Arboreal Echimyidae (Rodentia: Echimyidae, Echimyinae), With Descriptions of Two New Genera. pp. 247–310 in Lacey, E.A. & Myers, P. 2005. Mammalian Diversification: From Chromosomes to Phylogeography (A Celebration of the Career of James L. Patton). University of California Publications in Zoology. Head and body is 18-27.5 cm and tail is 17–30 cm. Weight is 320-570 grams.

Natural history

These animals appear to be

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...

, based on the shape of their hind feet. They are thought to spend the day in holes in the ground near trees.

Systematics

The etymology of the genus name ''Isothrix'' corresponds to the two

ancient greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...

words (), meaning "of equal length", and , (), meaning "hair". The etymology of the genus name synonym ''Lasiuromys'' corresponds to the three

words (), meaning "furry, with tufted hair", (), meaning "animal tail", and (), meaning "mouse, rat". There are currently five

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 ...

recognized in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Isothrix'': * '' Isothrix barbarabrownae''- Barbara Brown's Brush-tailed Rat * '' Isothrix bistriata'' - Yellow-crowned brush-tailed rat * '' Isothrix negrensis'' - Rio Negro brush-tailed rat * '' Isothrix pagurus'' - Plain brush-tailed rat * '' Isothrix sinnamariensis'' - Sinnamary brush-tailed rat There does appear to be good support for the

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

of three species found in this genus.

Phylogeny

''Isothrix'' is a member of the

Echimyini Echimyini is a tribe of echimyid rodents, proposed in 2016, and containing 13 extant genera: all of the tree rats '' Echimys'', '' Phyllomys'', '' Makalata'', ''Pattonomys'', '' Toromys'', '' Diplomys'', '' Santamartamys'', and '' Isothrix'', th ...

clade of

Echimyidae rodents. Although tentatively considered an echimyine, it has been suggested that ''Isothrix'' may not be particularly closely related to other members of its subfamily. This is confirmed by molecular phylogenies in which ''Isothrix'' appears as a distant relative of the three clades of

: (i) ''Echimys'', ''Phyllomys'', ''Makalata'', ''Pattonomys'', and ''Toromys'' ; (ii) the bamboo rats ''Dactylomys'', ''Olallamys'', ''Kannabateomys'' together with ''Diplomys'' and ''Santamartamys'' ; and (iii) the arboreal eumysopines ''Mesomys'' and ''Lonchothrix''. The taxon '' Callistomys pictus'' was previously member of the genus ''Isothrix'', but most authors considered it distinct enough to warrant a separate genus. This distinctness has been confirmed by DNA comparative studies in which ''Callistomys'' even appears to branch with members of a distinct tribe (i.e.,

Myocastorini Myocastorini is a tribe of echimyid rodents, proposed in 2017, and containing the five extant genera '' Callistomys'', '' Hoplomys'', '' Myocastor'', ''Proechimys ''Proechimys'' is a genus of South American spiny rats of the family Echimyida ...

) of the subfamily Echimyinae. The arboreal genera of the subfamily Echimyinae therefore constitute a

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

assemblage.

References

{{Taxonbar, from=Q911355 Rodent genera Taxa named by Johann Andreas Wagner