During the Mesozoic, when the Earth became much warmer, 251 to 140 Ma, the Australian landmass was covered with riverine plains. Humid conditions allowed the formation of peatlands, particularly in the east. Dinosaurs, reptiles and primitive mammals were present in Australia. Between 140 and 99 Ma sea levels rose and much of the continent was covered. In the same period (between 120 - 105 Ma) there was more volcanism in eastern Australia, leading to uplift creating the Tasman Sea to the southeast and the Coral Sea to the north.