Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. The word "lemur" derives from the word lemures (ghosts or spirits) from Roman mythology and was first used to describe a slender loris due to its nocturnal habits and slow pace, but was later applied to the primates on Madagascar. Although lemurs often are confused with ancestral primates, the anthropoid primates (monkeys, apes, and humans) did not evolve from them; instead, lemurs merely share morphological and behavioral traits with basal primates. Lemurs arrived in Madagascar around 62 to 65 mya by rafting on mats of vegetation at a time when ocean currents favored oceanic dispersal to the island. Since that time, lemurs have evolved to cope with an extremely seasonal environment and their adaptations give them a level of diversity that rivals that of all other primate groups. Until shortly after humans arrived on the island around 2,000 years ago, there were lemurs as large as a male gorilla. Today, there are nearly 100 species of lemurs, and most of those species have been discovered or promoted to full species status since the 1990s; however, lemur taxonomic classification is controversial and depends on which species concept is used. Even the higher-level taxonomy is disputed, with some experts preferring to place most lemurs within the infraorder Lemuriformes, while others prefer Lemuriformes to contain all living strepsirrhines, placing all lemurs in superfamily Lemuroidea and all lorises and galagos in superfamily Lorisoidea.