The early Permian saw the collision of the landmasses of Laurentia and Gondwanaland. This was followed by the fusion of proto Siberia, Angara, to form the vast proto continent, Pangea, surrounded by the ocean of Panthalassa. At the same time, the constituents of modern South and East Asia sheared from eastern Gondwanaland in the early Permian and began to drift west across the Tethys Ocean. The Permian began with an ice age, but the climate gradually warmed and the interior of Pangea desertified, although there were alternating cooler spells. The dominant land fauna were amphibians and, increasingly, reptiles, including the mammalian ancestors, the cynodonts, and the diapsid forerunners of the dinosaurs. Sail-backed reptiles, such as Dimetrodon, typify the fauna of the era; the device was possibly a means of controlling body temperature in the Pangean deserts. Primitive dragonflies and cockroaches were widespread, and, amongst plant forms, conifers supplanted the swamp-loving lycopods of the Carboniferous.