The bristle-spined rat (''Chaetomys subspinosus'') is an
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 (scansorial), but others are exclusively arboreal. The hab ...
rodent from the
Atlantic forest in eastern
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
. Also known as the bristle-spined porcupine or thin-spined porcupine, it is the
only member of the
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''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 () 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 (state), São Paulo, Mina ...
. Since then it has been recorded at several localities in eastern Brazil, from
Sergipe
Sergipe (), officially State of Sergipe, is a States of Brazil, state of Brazil. Located in the Northeast Region, Brazil, Northeast Region along the Atlantic Ocean, Atlantic coast of the country, Sergipe is the smallest state in Brazil by geogra ...
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 attracti ...
(there are no recent records from
Rio de Janeiro
Rio de Janeiro, or simply Rio, is the capital of the Rio de Janeiro (state), state of Rio de Janeiro. It is the List of cities in Brazil by population, second-most-populous city in Brazil (after São Paulo) and the Largest cities in the America ...
), but it remains rare and threatened due to habitat loss,
poaching
Poaching is the illegal hunting or capturing of wild animals, usually associated with land use rights.
Poaching was once performed by impoverished peasants for subsistence purposes and to supplement meager diets. It was set against the huntin ...
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 that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origin ...
. 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 an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
. It is classified as vulnerable by the
IUCN
The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
[ and endangered by the U.S. Fish and Wildlife Service.][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 terr ...
. Both are South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
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 foram ...
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 Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
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, wher ...
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 or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...
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 used ...
gene coding for cytochrome b
Cytochrome b is a protein found in the membranes of aerobic cells. In eukaryotic mitochondria (inner membrane) and in aerobic prokaryotes, cytochrome b is a component of respiratory chain complex III () — also known as the bc1 complex or ubiq ...
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 of Pymatuning Lake in Pennsylva ...
Special Publication, 6:377-392.
External links
Animal Diversity Web page on ''Chaetomys''
{{Taxonbar, from=Q894229
Erethizontidae
Rodents of Brazil
Endemic mammals of Brazil
Fauna of the Atlantic Forest
Mammals described in 1818
Taxa named by Ignaz von Olfers
ESA endangered species