Isothrix

The toros or brush-tailed rats, genus Isothrix, are a group of spiny rats^[1] found in tropical South America, particularly in the Amazon Basin.^[2]

Isothrix Temporal range: Pleistocene - Recent
Isothrix bistriata
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Echimyidae
Subfamily:	Echimyinae
Tribe:	Echimyini
Genus:	Isothrix Wagner, 1845
Type species
Isothrix bistriata
Species
I. barbarabrownae I. bistriata I. negrensis I. pagurus I. sinnamariensis
Synonyms
Lasiuromys Deville, 1852

Description

Toros look like large rats with soft fur on the body and long guard hairs on the scaly tail.^[3] Head and body is 18-27.5 cm and tail is 17–30 cm.^[2] Weight is 320-570 grams.

Natural history

These animals appear to be arboreal, based on the shape of their hind feet.^[2] 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 ἴσος (ísos), meaning "of equal length", and θρίξ, τριχός (thríx, trikhós), meaning "hair".^[4][5] The etymology of the genus name synonym Lasiuromys corresponds to the three ancient greek words λάσιος (lásios), meaning "furry, with tufted hair", οὐρά (ourá), meaning "animal tail", and μῦς (mûs), meaning "mouse, rat".^[4][5]

There are currently five species recognized in the genus Isothrix:^[6]

• Isothrix barbarabrownae^[7]- 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 of three species found in this genus.^[3]

Phylogeny

Isothrix is a member of the Echimyini clade of arboreal Echimyidae rodents.^[8] Although tentatively considered an echimyine, it has been suggested that Isothrix may not be particularly closely related to other members of its subfamily.^[3] 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.^[9]

The taxon Callistomys pictus was previously member of the genus Isothrix, but most authors considered it distinct enough to warrant a separate genus.^[10] 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.^[11][8][9] The arboreal genera of the subfamily Echimyinae therefore constitute a polyphyletic assemblage.

Genus-level cladogram of the Echimyini.

Echimyini              Isothrix   "Eumysopines"     Lonchothrix   (Tuft-tailed spiny tree-rat)   Mesomys                                           Pattonomys   Toromys   (Giant tree-rat)             Makalata   Echimys   Phyllomys   Diplomys   Santamartamys   (Red-crested tree-rat)   "Dactylomyines"     Kannabateomys   (Atlantic bamboo rat)             Dactylomys   Olallamys

The cladogram has been reconstructed from mitochondrial and nuclear DNA characters.[12][13][14][15][16][11][17][18][8][9]

References

1. Wilson, D. E.; Reeder, D. M., eds. (2005). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494.
2. Nowak, Ronald M. 1999. Walker's Mammals of the World, 6th edition. Johns Hopkins University Press, 1936 pp. ISBN 0-8018-5789-9
3. 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.
4. Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN 978-2010035289. OCLC 461974285.
5. Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved December 23, 2017.
6. Woods, C.A.; Kilpatrick, C.W. (2005). "Genus Isothrix". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 1538–1600. ISBN 978-0-8018-8221-0. OCLC 62265494.
7. "New squirrel-like rodent discovered in Peru". New Scientist. 2007-01-24. Retrieved 2011-11-23.
8. Fabre, Pierre-Henri; Patton, James L.; Leite, Yuri L. R. (2016). "Family Echimyidae (hutias, South American spiny-rats and coypu)". In Wilson, Don E.; Lacher, Thomas E. Jr; Mittermeier, Russell A. (eds.). Handbook of the Mammals of the World. Vol 6. Lagomorphs and Rodents I. Barcelona: Lynx Edicions. pp. 552–641. ISBN 978-84-941892-3-4.
9. Fabre, Pierre-Henri; Upham, Nathan S.; Emmons, Louise H.; Justy, Fabienne; Leite, Yuri L. R.; Loss, Ana Carolina; Orlando, Ludovic; Tilak, Marie-Ka; Patterson, Bruce D.; Douzery, Emmanuel J. P. (2017-03-01). "Mitogenomic Phylogeny, Diversification, and Biogeography of South American Spiny Rats" (PDF). Molecular Biology and Evolution. 34 (3): 613–633. doi:10.1093/molbev/msw261. ISSN 0737-4038. PMID 28025278.
10. Woods, C.A.; Kilpatrick, C.W. (2005). "Genus Callistomys". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 1538–1600. ISBN 978-0-8018-8221-0. OCLC 62265494.
11. Loss, Ana; Moura, Raquel T.; Leite, Yuri L. R. (2014). "Unexpected phylogenetic relationships of the painted tree rat Callistomys pictus (Rodentia: Echimyidae)" (PDF). Natureza on Line. 12: 132–136. Archived from the original (PDF) on 2021-06-23. Retrieved 2017-12-22.
12. Lara, Márcia C.; Patton, James L.; da Silva, Maria Nazareth F. (1996). "The Simultaneous Diversification of South American Echimyid Rodents (Hystricognathi) Based on Complete Cytochrome b Sequences". Molecular Phylogenetics and Evolution. 5 (2): 403–413. doi:10.1006/mpev.1996.0035. PMID 8728398.
13. Leite, Yuri L. R.; Patton, James L. (2002). "Evolution of South American spiny rats (Rodentia, Echimyidae): the star-phylogeny hypothesis revisited". Molecular Phylogenetics and Evolution. 25 (3): 455–464. doi:10.1016/s1055-7903(02)00279-8.
14. Galewski, Thomas; Mauffrey, Jean-François; Leite, Yuri L. R.; Patton, James L.; Douzery, Emmanuel J. P. (2005). "Ecomorphological diversification among South American spiny rats (Rodentia; Echimyidae): a phylogenetic and chronological approach". Molecular Phylogenetics and Evolution. 34 (3): 601–615. doi:10.1016/j.ympev.2004.11.015. PMID 15683932.
15. Upham, Nathan S.; Patterson, Bruce D. (2012). "Diversification and biogeography of the Neotropical caviomorph lineage Octodontoidea (Rodentia: Hystricognathi)". Molecular Phylogenetics and Evolution. 63 (2): 417–429. doi:10.1016/j.ympev.2012.01.020. PMID 22327013.
16. Fabre, Pierre-Henri; Galewski, Thomas; Tilak, Marie-ka; Douzery, Emmanuel J. P. (2013-03-01). "Diversification of South American spiny rats (Echimyidae): a multigene phylogenetic approach". Zoologica Scripta. 42 (2): 117–134. doi:10.1111/j.1463-6409.2012.00572.x. ISSN 1463-6409.
17. Fabre, Pierre-Henri; Vilstrup, Julia T.; Raghavan, Maanasa; Der Sarkissian, Clio; Willerslev, Eske; Douzery, Emmanuel J. P.; Orlando, Ludovic (2014-07-01). "Rodents of the Caribbean: origin and diversification of hutias unravelled by next-generation museomics". Biology Letters. 10 (7): 20140266. doi:10.1098/rsbl.2014.0266. ISSN 1744-9561. PMC 4126619. PMID 25115033.
18. Upham, Nathan S.; Patterson, Bruce D. (2015). "Evolution of Caviomorph rodents: a complete phylogeny and timetree for living genera". In Vassallo, Aldo Ivan; Antenucci, Daniel (eds.). Biology of caviomorph rodents: diversity and evolution. Buenos Aires: SAREM Series A, Mammalogical Research — Sociedad Argentina para el Estudio de los Mamíferos. pp. 63–120.