Naked mole-rats Heterocephalus glaber are highly social hystricomorph rodents endemic to the arid regions of East Africa. Living entirely underground, they excavate an extensive system of tunnels with their continuously growing extra-buccal incisors. The majority of the burrow is composed of foraging tunnels, constructed in search of the underground roots and tubers that form their staple diet. Subterranean foraging imposes risks associated with not finding food, and a high energetic cost, and in addition could be limited by the rate of wear of the incisor teeth. The aim of this study was to determine eruption rates for mandibular incisors in naked mole-rats to investigate whether they showed evidence of faster eruption as an adaptation to their subterranean niche and mode of digging. Impeded eruption rates (when the teeth were left in normal occlusion) were initially determined over a period of 1 week in a group of 12 naked mole-rats kept in laboratory conditions. Unimpeded eruption rates were then monitored in the same animals by cutting one mandibular incisor free of occlusion thrice weekly, and measuring growth over a 2-week period. Mean daily impeded eruption rates were c. 228.7±17.5 μm, while mean daily unimpeded rates were higher at c. 624.7±10.4 μm. While impeded eruption rates under laboratory conditions may be an underestimate of the rates occurring in the wild, unimpeded rates (usually about twice the impeded rate) indicate the maximum potential eruption rates of the teeth and are independent of functional activity. These data are not dissimilar from those determined for laboratory rodents and lagomorphs suggesting that the naked mole-rat does not display unusual patterns of eruptive behaviour. Tooth wear resulting from their subterranean lifestyle may be offset as a limiting factor by the social behaviour of the naked mole-rat, where digging activity is distributed among a large workforce during favourable burrowing conditions.

Tooth succession was followed in captive greater cane rats Thryonomys swinderianus of known ages with the aid of regular radiographs. The incisors and single premolar tooth (dP 4/4) in each quadrant are persistent deciduous teeth that are not replaced by permanent teeth. Tooth succession is relatively slow, with eruption of the lower cheek teeth in advance of the upper ones. During the first 5 months of post-natal development, three cheek teeth per quadrant become functional. Another 5 months elapse before the fourth cheek tooth erupts. The same slow growth can be seen in the increase in mass, which only doubles 5 months after puberty (5 months).