(background), Ophiacodon and Varanops'' Some species were quite large, growing to a length of or more, although most species were much smaller. Well-known pelycosaurs include the
genera Dimetrodon,
Sphenacodon,
Edaphosaurus, and
Ophiacodon. Pelycosaur fossils have been found mainly in
Europe and
North America, although some small, late-surviving forms are known from
Russia and
South Africa. Unlike
lepidosaurian reptiles, pelycosaurs might have lacked reptilian epidermal
scales. Fossil evidence from some
varanopids shows that parts of the skin were covered in rows of
osteoderms, presumably overlain by horny
scutes. Parts of the skin
not covered in scutes might have had naked, glandular skin like that found in some mammals. Dermal scutes are also found in a diverse number of extant mammals with conservative body types, such as in the tails of some
rodents,
sengis,
moonrats, the
opossums, and other
marsupials, and as regular dermal armour with underlying bone in the
armadillo. At least two pelycosaur
clades independently evolved a tall
sail, consisting of elongated vertebral spines: the
edaphosaurids and the
sphenacodontids. In life, this may have been covered by skin, and likely functioned as a
thermoregulatory device or as a
mating display. ==Taxonomy==