The prehistoric landbridge came down from the Malay peninsula through modern Indonesia and across the Timor Sea. Tasmania was at that time also a part of the landmass and
Bass Strait (between Melbourne and Devonport) was dry.
I have actually exhausted my knowledge of the background and history of prehistoric Australian Indigenes. I am a modern historian by interest. This is the stuff I picked up in my readings relating to the treatment of Aboriginals by white folks, a truly contentious subject here as no doubt it is with you.
Your earlier guess Gafftaper about the creation of Oceania being a geographer rather than geologer driven concept is probably correct. I had not heard that clims went as far as the Alaskan islands though although I knew that the inclusion of Hawaii was an issue.
The racial mix throughout Oceania is stunning, Indonesia and the Phillipines seem to have a basic racial mix related very closely to SE Asia while Papua New Guinea and the Timorese are yet another group also apparently unrelated to the Australian Aboriginal. The Maori of New Zealand are Polynesian and related to the residents of Tahiti Samoa Tonga and Hawaii but I am not sure where the Fijians fit in all this, they seem to be a different group.
I've run out again.