Genus of mammals belonging to the spiny rat family of rodents
The toros or brush-tailed rats, genus Isothrix, are a group of spiny rats found in tropical South America, particularly in the Amazon Basin.
Description.
Toros look like large rats with soft fur on the body and long guard hairs on the scaly tail. 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, 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 words (), meaning "of equal length", and , (), meaning "hair". The etymology of the genus name synonym "Lasiuromys" corresponds to the three ancient greek words (), meaning "furry, with tufted hair", (), meaning "animal tail", and (), meaning "mouse, rat".
There are currently five species recognized in the genus "Isothrix":
There does appear to be good support for the monophyly of three species found in this genus.
Phylogeny.
"Isothrix" is a member of the Echimyini clade of arboreal 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 Echimyini: (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) of the subfamily Echimyinae. The arboreal genera of the subfamily Echimyinae therefore constitute a polyphyletic assemblage.
References.
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