Petromus typicus, A. Smith, 1831

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Petromuridae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 336-337 : 337

Noki

Petromus typicus

French: Noki / German: Felsenratte / Spanish: Noki

Other common names: Dassie Rat, Rock Rat

Taxonomy. Petromus typicus A. Smith, 1831 ,

“mountains of Little Namaqualand,” Northern Cape Province, South Africa.

Although numerous forms and subspecies have been described, preliminary and not yet published cranial measurements carried out by C. G. Coetzee and C. T. Chimimba are consistent with P. typcus being monotypic. Although this should be confirmed by phylogenetic analyses, this is provisionally accepted here. Monotypic.

Distribution. From 16° S and 12° E in SW Angola S through W Namibia to 30° S and 18° E in NW South Africa.

Descriptive notes. Head-body 135-224 mm, tail 116-175 mm; weight 88-285 g. The Nokiis a small rodent that looks like a blend ofrat and squirrel. It is remarkably adapted to live in narrow crevices because ofits strongly flattened skull and flexible ribs that allow a dorsoventral compression of the body without damage. Furthermore, mammae are situated laterally at the level of the scapula, which permits young to suckle when females are squeezed into rock crevices. Coat is long and soft with no underfur, variable in color according to locality but predominantly of shades of gray, brown, and yellowish. Nokis have short limbs, feet with naked soles and well-developed pads; forefeet with four digits (first one is rudimentary), three plantar pads at bases of digits and two on palm; hindfeet with five toes, three plantar pads at bases of toes and one on palm; and all digits with short claws. Incisors are smooth and opisthodont; cheekteeth are rooted and hypsodont, with a very simplified crown pattern; dental formulais I 1/1, C 0/0,P1/1,M 3/3 (3) = 20. The Noki has a large almost U-shaped stomach without proventriculus, a large cecum strongly subdivided, and proximal colon with colon separating mechanism. Renal anatomy of Nokis suggests that kidneys are efficiently adapted to concentrate urine, but even if they have low water requirements, captive Nokis cannot survive water deprivation for more than c.3 weeks on a diet of air-dried seed.

Habitat. Arid and semiarid mountainous areas and isolated rock hills (kopjes), or small mountains that rise abruptly from surrounding plains (inselbergs). Nokis depend on availabilities of shelter and nesting sites, and they live in rocky crevices, canyons, mountain slopes, and rocky drainages that provide shelter (nature of the rock itself is not a limiting factor). Piled up boulders frequently provide nesting sites for Nokis.

Food and Feeding. The Nokiis herbivorous. It feeds on a wide variety of plants, but it prefers fresh leaves and stems,fruits, and flowers when available. It is an opportunistic feeder, and although not very selective, it does prefer some plants to others. It favors grass leaves and bases of grass stems that have higher water content than tops. It seems to avoid grass seed heads, which is quite surprising in view of their higher energy content compared with leaves and stems. Upper parts of kopjes, where Nokis often live, are devoid of plant cover, which forces them to go down rocky hills to find food. They always remain near rocks forsafety. They bring food to their sheltersto eat it, but they do not store or cache food. Enlarged cecum and coprophagy favor post-gastric fermentation. Nokis obtain water from the plant matter they eat, but they drink free water if given the opportunity. Despite kidneys well adapted to excrete highly concentrated urine, Nokis cannot survive long without water.

Breeding. Breeding takes place mainly in spring in winter-rainfall areas and in autumn in summer-rainfall areas, probably related to sprouting of plants following rains. The Noki is monogamous; gestation is relatively long as in other hystricomorph rodents (c.3 months). One litter is produced annually, with a mean size of two young. As in most hystricomorph rodents, young Nokis are precocial at birth, with eyes and ears open and fully furred and with the ability to run and jump after ¢.10 minutes from birth. Females have 2-3 pairs of nipples; two pairs are dorso-laterally located so they can feed their young while hiding in very narrow crevices. Young are nursed for 2-5 minutes, several times a day, and they are weaned at c.3 weeks old. Weights of young at birth are 10-5-20 g. At ¢.3 weeks old, average weight is c.45 g, and at c¢.3 months old, itis c.115 g. Adulthood is reached near the age of c.9 months and a mass of ¢.150 g.

Activity patterns. The Nokiis a diurnal and particularly active early in the morning and late in the afternoon. Nokis sunbathe, forage, rest in shadows, and engage in other activities such as grooming or watching for threats. Nokis forage near their shelters, and they always try to minimize exposure to the sun and predators. They run toward food, eating or collecting it rapidly before quickly returning to safety of the rocks. When not foraging, they sunbathe on hot rocks and move between sunny and shady places to regulate their body temperatures. When disturbed, they run fast to hide. Nokis dust-bathe near their shelters; they loosen soil by scratching it with their front feet and then roll on it several times. Social grooming happens at any time during the day, but self-grooming takes place in the morning. Nokis defend territories. At least one Noki watches surroundings from the top of rocks to detect potential predators and conspecific intruders. Nokis emit alarm calls if they see a predator.

Movements, Home range and Social organization. Nokis usually live in small family groups that can be close to other family groups, forming some type of colony. Males are intolerant with other males, whereas females tolerate each other and intruding males. Home ranges of males and females contract greatly after birth of young, particularly during the first week when one parent always stays with young. Nokis are monogamous and form strong social bonds, with low levels of intergenerational aggression. Mate guarding seems to be important in evolution of social monogamy of Nokis. During the first week, males spent nearly as much time with young as do females; males spend increasingly less time with young as they grow older. Both parents are very protective with their offspring.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Noki is largely confined to a narrow band from South Africa crossing all of Namibia. It does not extend into Angola out of the desert or scrublands areas of the sunny south-west. It is restricted in Namibia to the western one-half of the country (except for the coast), not extending eastward into the Kalahari. In South Africa, the Nokiis limited to the desert and semi-desert zones of the westernmost end of the country, not adventuring into dry steppes of the interior or those of the Kalahari in the north. Nokis are not declining at rates to be included in a threatened conservation category.

General Bibliography. Barbiére & Marivaux (2015), Coetzee (2002, 2013), De Graaff (1997), George (1981b), George & Crowther (1981), Griffin & Coetzee (2008), Huchon & Douzery (2001), Huchon et al. (2007), ICZN (1999), Lavocat (1973), Macdonald (2009), Mein & Pickford (2006), Mess & Ade (2005), Monadjem et al. (2015), Nedbal et al. (1996), Nowak (1999c¢), Pickford et al. (1994), Rathbun & Rathbun (2005, 2006a, 2006b), Roberts (1951), Scott (1990), Sénégas (2004), Shortridge (1934a), Skinner & Chimimba (2005), Smith (1831, 1834, 1849), Tullberg (1899), Van der Merwe (2004a), Winkler et al. (2010), Withers (1979), Withers et al. (1980), Wood (1955), Woods & Kilpatrick (2005).

Figures

Noki

Distribution. From 16° S and 12° E in SW Angola S through W Namibia to 30° S and 18° E in NW South Africa.