Continent world ultimately persisted with these being regarded as separate continents. From the late 18th century, some geographers started to regard North America and South America as two parts of the world, making five parts in total. Overall though, the fourfold division prevailed well into the 19th century. Europeans discovered Australia in 1606, but for some time it was taken as part of Asia. By the late 18th century, some geographers considered it a continent in its own right, making it the sixth (or fifth for those still taking America as a single continent). In 1813, Samuel Butler wrote of Australia
Smallest organisms montane environments. There is relatively little data on size variation among individuals, growth from metamorphosis to adulthood or size variation among populations in these species. Additional studies and the discovery of further minute frog species are likely to change the rank order of this list. The dwarf gecko ("Sphaerodactylus ariasae") and the Virgin Islands dwarf sphaero ("S. parthenopion"), two geckos in the genus "Sphaerodactylus", are the world's smallest known reptile species and smallest lizard, with a snout-vent length of . A few "Brookesia" chameleons from Madagascar are equally small, with a reported snout-vent length of 15–18 millimetres for male dwarf