that they, too, exhibited female social dominance, possibly exhibiting the same levels of agonism (aggressive competition) seen in extant lemurs. Like other lemurs, they had smaller brains than comparably sized anthropoids. Most species also had a unique strepsirrhine dental trait, called a toothcomb, which is used for grooming. Even tooth development and weaning was rapid compared to similarly sized anthropoids, suggesting faster sexual maturity of their offspring. Most subfossil lemurs also had high retinal summation (sensitivity to low light), resulting in poor day vision (low visual acuity) compared to anthropoids. This has been demonstrated by the ratio between their relatively small orbits (eye sockets) and the relative size of their optic canal, which is comparable to that of other lemurs, not diurnal anthropoids. These traits are shared among both living and extinct lemurs, but are uncommon among primates in general. Two prevailing hypotheses to explain these unique adaptations are the energy frugality hypothesis by Patricia Wright (1999) and the evolutionary disequilibrium hypothesis by Carel van Schaik and Peter M. Kappeler (1996). The energy frugality hypothesis expanded on Alison Jolly's energy conservation hypotheses by claiming that most lemur traits not only help conserve energy, but also maximize the use of highly limited resources, enabling them to live in severely seasonal environments with low productivity. The evolutionary disequilibrium hypothesis postulated that living lemurs are in the process of evolving to fill open ecological niches left by the recently extinct subfossil lemurs. For example, small nocturnal prosimians are typically nocturnal and monogamous, while the larger living lemurs are generally active both day and night (cathemeral) and live in small groups (gregarious). Cathemerality and increased gregariousness might indicate that the larger living lemurs are evolving to fill the role of the giant lemurs, which were thought to be diurnal (day-living) and more monkey-like in behavior. Since most giant subfossil lemurs have been shown to share many of the unique traits of their living counterparts, and not those of monkeys, Godfrey et al. (2003) argued that the energy frugality hypothesis seems to best explain both living and extinct lemur adaptations. Despite the similarities, subfossil lemurs had several distinct differences from their lemur relatives. In addition to being larger, the subfossil lemurs were more dependent on leaves and seeds in their diet, rather than fruit. They utilized slow climbing, hanging, and terrestrial quadrupedalism for locomotion, rather than vertical clinging and leaping and arboreal quadrupedalism. Also, all