The bristle-spined rat (''Chaetomys subspinosus'') is an
arboreal
Arboreal locomotion is the Animal locomotion, 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. Th ...
rodent from the
Atlantic forest
The Atlantic Forest ( pt, Mata Atlântica) is a South American forest that extends along the Atlantic coast of Brazil from Rio Grande do Norte state in the northeast to Rio Grande do Sul state in the south and inland as far as Paraguay and th ...
in eastern
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. Also known as the bristle-spined porcupine or thin-spined porcupine, it is the
only member of the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Chaetomys'' and the subfamily Chaetomyinae.
It was officially described in 1818, but rarely sighted since, until December 1986, when two specimens - one a pregnant female - were found in the vicinity of Valencia in
Bahia
Bahia ( , , ; meaning "bay") is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (sta ...
. Since then it has been recorded at several localities in eastern Brazil, from
Sergipe
Sergipe (), officially State of Sergipe, is a state of Brazil. Located in the Northeast Region along the Atlantic coast of the country, Sergipe is the smallest state in Brazil by geographical area at , larger only than the Federal District. Serg ...
to
Espírito Santo
Espírito Santo (, , ; ) is a state in southeastern Brazil. Its capital is Vitória, and its largest city is Serra. With an extensive coastline, the state hosts some of the country's main ports, and its beaches are significant tourist attra ...
(there are no recent records from
Rio de Janeiro
Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...
), but it remains rare and threatened due to habitat loss, poaching and roadkills.
Characteristics
Bristle-spined rats are named because the spines on the back are more bristle-like in texture than the spines on the rest of the body. They have long, naked tails which are not
prehensile
Prehensility is the quality of an appendage or organ (anatomy), organ that has Adaptation (biology), adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely der ...
. Adult animals weigh around .
Their skulls are unusual in several ways. The eye socket is almost completely surrounded by a ring of bone. Incisors are distinctly narrow. Overall, the animal displays a mix of New World porcupine cranial characters, spiny rat cranial characters, and characters that set it apart from all other rodents.
The bristle-spined rat is restricted to remnant forests and forest edges in the Atlantic coastal forests on the east coast of Brazil. Its habitat is dwindling rapidly and the species may be vulnerable to
extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
. It is classified as vulnerable by
IUCN
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
and endangered by
USDI.
[Nowak, 1999]
Taxonomic controversy
No consensus has been reached as to the taxonomic position of ''Chaetomys''. It is commonly placed with the New World porcupines in the family
Erethizontidae or with the spiny rats the family
Echimyidae
Echimyidae is the family of neotropical spiny rats and their fossil relatives. This is the most species-rich family of hystricognath rodents. It is probably also the most ecologically diverse, with members ranging from fully arboreal to terres ...
. Both are
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 southe ...
n
hystricognath
The Hystricognathi are an infraorder of rodents, distinguished from other rodents by the bone structure of their skulls. The masseter medialis (a jaw muscle) passes partially through a hole below each eye socket (called the infraorbital foramen) ...
s with hairs modified as spines or quills. ''Chaetomys'' has more highly developed spines than the spiny rats, but less developed than the porcupines. Characteristics of the
premolar
The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
suggest that it belongs with the Echimyidae, but characteristics of the
incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...
enamel suggest that it belongs in the Erethizontidae.
Patterson and Pascual (1968), Patterson and Wood (1982), Woods (1982, 1984, 1993) Patton and Reig (1989), Nowak (1999), and Carvalho (2000) support the inclusion of this animal in Echimyidae whereas Martin (1994), McKenna and Bell (1997), Carvalho and Salles (2004), and Woods and Kilpatrick (2005) argue that it belongs in Erethizontidae. Emmons (2005) mentions the family Chaetomyidae without much further comment except to exclude it from Echimyidae.
A molecular
phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
based on the
mitochondrial
A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...
gene coding for
cytochrome b
Cytochrome b within both molecular and cell biology, is a protein found in the mitochondria of eukaryotic cells. It functions as part of the electron transport chain and is the main subunit of transmembrane cytochrome bc1 and b6f complexes.
F ...
combined to
karyological evidence actually suggests that ''Chaetomys'' is more closely related to the Erethizontidae than to the Echimyidae, although it branches as the sister group to the rest of the Erethizontidae.
References
Further reading
*Carvalho, 2000. Substitution of the deciduous premolar in ''Chaetomys subspinosus'' (Olfers, 1818) (Hystricognathi, Rodentia) and its taxonomic implications. Zeitschrift für Säugetierkunde, 65:187-190.
*Carvalho, G. A. S. and L. O. Salles. 2004. Relationships among extant and fossil echimyids. Zoological Journal of the Linnean Society, 142:445-477.
*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.
*Martin, T. 1994. On the systematic position of ''Chaetomys subspinosus'' (Rodentia: Caviomorpha) based on evidence from the incisor enamel microstructure. Journal of Mammalian Evolution, 2:117-131.
*McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp.
*Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.
*Patton, J. L. and O. A. Reig. 1989. Genetic differentiation among echimyid rodents, with emphasis on spiny rats, genus ''Proechimys''. pp. 75–96 in Neotropical Mammalogy (K. H. Redford and J. F. Eisenberg, eds.). Sandhill Crane Press, Gainesville.
*Patterson, B. and R. Pascual. 1968. New echimyid rodents from the Oligoceneof Patagonia, and a synopsis of the family. Brevioria, 301:1-14.
*Patterson, B. and A. E. Wood. 1982. Rodents from the Deseadan Oligocene of Bolivia and the relationships of the Caviomorpha. Bulletin of the Museum of Comparative Zoology, 149:371-543.
*Woods, C. A. 1982. The history and classification of the South American hystricognath rodents: Reflections on the far away and long ago.
Pymatuning Laboratory of Ecology
The Pymatuning Laboratory of Ecology (PLE) is a year-round ecology field station of the University of Pittsburgh Department of Biological Sciences located in Linesville and South Shenango Township on the shores Pymatuning Lake in Pennsylvania. Th ...
Special Publication, 6:377-392.
External links
Animal Diversity Web page on ''Chaetomys''
{{Taxonbar, from=Q894229
Erethizontidae
Rodents of South America
Mammals of Brazil
Endemic fauna of Brazil
Mammals described in 1818
Taxa named by Ignaz von Olfers