The lost Australian Civilization. I am guessing Old Australia, the East Coast, was settled by ancestors of today's Pacific Islanders. These would have been Denisovians, people of Phillipino (or Olmec) appearance, Chinese, Long Ears (an unknown race of redheads from Asia), etc, etc, etc. There was also an African-looking people living in the Pilbara/Kimberley, responsible for the Bradshaw Art.
This video in which I talk perhaps a little too quickly, describes the lost stone circle complexes of Australia. Almost all were destroyed by farmers, unfortunately.