*(1(5$/ $63(&76 2) 52'(17 %,2/2*< The first rodents appeared 60 â&#x20AC;&#x201C; 65 million years ago. They are now the most common species in the mammalian order, with about 3000 extant species (compared with the 236 species of Carnivora). They live in all parts of the world and a variety of ecological niches. Despite, this, they are relatively conservative in morphology â&#x20AC;&#x201C; all are herbivores or at least primarily herbivorous; all are small (the largest extant species being the capybara); nearly all of them are terrestrial; and many are burrowers. They also have small brains and cerebral hemispheres (though it should be emphasised that some species, e.g. the rat, show excellent learning and memory). Their success stems from their rapid reproductive rates (females are typically polyoestrous, producing litters throughout the year), and their specialised dentition and associated musculature. Their incisors are reduced to four in number. They are enlarged, continuously growing, and have enamel only on their labial (i.e. outer) surfaces so that differential wear of the enamel and dentine results in a constantly sharp chisel-like edge. Their cheek muscles (the masseters) are enlarged and modified so as to produce enhanced jaw mobility and a powerful gnawing action. Rodents are also characterised by excellent smell (the olfactory bulbs are typically very well developed) and hearing; vision is also well-developed in arboreal and open-grassland species. Rodent herbivory is aided by hindgut fermentation and many species exhibit coprophagia in order to maximise the absorption of nutrients released by this process. The general biological characteristics of rodent species used for fur production are summarized in table 4. Table 4.: Biological characteristics of rodent species used for fur production Coypu Chinchilla Average body mass (kg) Average home range Diet Activity cycles Denning habits Adult social structure Average litter size Weaning (weeks) Sexual maturity (months) Mortality and longevity Other features
F: 5-6 M: 6-7 F: 2.5ha M: 5.7 Herbivorous Nocturnal/crepuscular Digs own burrows Gregarious (2-15 animals) Polygamous mating 5-6 8 6 Unknown, Up to 7 years Semi-aquatic, territories along water, excellent swimmer and diver
F: 0.8 M: 0.5 Herbivorous Nocturnal Digs own burrows Gregarious, monogamous or possibly polyandrous 2-3 6-8 8 Unknown, Up to 10 years Desert living
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The higher-level classification of the coypu is controversial. Though coypus are related to echimyids and capromyids, several morphological differences argue against uniting myocastorids with either of these taxa in the same family. Therefore, currently the coypu is placed in its own family, Myocastoridae (Woods et al., 1992).
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