The POD is that Homo Erectus somehow reaches Australia and the native megafauna have time to adapt to hominoid hunting. Then when the Europeans arrive they discover some truly terrifying animals :0 There was a species of Marsupial Lion called Thyalcoleo Carnifex which 101-130 kg in weight, with a bite comparable to an African Lion. Not to mention a giant monitor lizard at least as big as a Komodo dragon calle Megalania and a Anaconda sized snake called Wonambi.
Or at least reindtroduce the Komodo Dragon back like suggested here in this wonderful article:
The Komodo Dragon: Even Deadlier Than You Thought
by theitinerantnaturalist
"The name "Komodo dragon" is a bit of misnomer. While this lizard found only in the Lesser Sundas today (specifically the islands of Komodo, Rinca, Padar, Gili Motang, and Flores), this limited distribution is artificial, a mere shadow of the glory that this empire of dragons used to hold. Komodo dragons evolved in Australia, and from there colonized Indonesia. And it was far from alone. From the same common ancestor arose an entire radiation of giant monitor lizards, and the Komodo dragon was merely the first of many to come. Later came the even larger Megalania (Varanus priscus), a titan weighing well over half a ton that ruled Australia, and the Timorean Dragon (Varanus sp.), a lizard larger than the Komodo dragon that reigned supreme on its namesake island. As the ice ages came and went, the Komodo dragon used the land bridges created by lower sea levels to island-hop its way all the way to Sundaland, the part of Indonesia that currently is partly flooded and contains Sumatra, Java and Bali. Here they came into contact with modern tigers, but it appears that the reptiles were competent enough to hold their own, as they coexisted as apex predators. But the good times did not last. Around 300,000 years ago, Sundaland became flooded, killing off the Timorean Dragon and the Asian population of the Komodo dragon. Megalania and other populations of Komodo dragons, however, adapted well to environmental changes.
Their demise would be caused not by natural events, but by our own species. The final blow came when humans arrived in Australia. By hunting the prey species eaten by giant lizards, and altering the ecosystems in general through use of fire, they managed to eat Megalania out of house and home, causing its extinction. This event also killed off every Australian land animal over 250 pounds in weight, and likely led to the Komodo dragon' demise there, leading to eastern Indonesia becoming the last remnant of the dragon dynasty. The Komodo dragons there got lucky: the island of Flores was home to a small hominid species (Homo floresiensis), so they had time to adapt to hominid incursions while the rest of their species were struck without warning. Personally I think it would be great to de-extinct megalania and reintroduce it and the Komodo dragon to Australia: Australian ecosystems need them still. You would expect, from their formerly widespread range, that Komodo dragons can live in an array of habitats. You'd be right. On their island homes they do well both in closed rain forests and open savannahs, as well as scrubby areas, thickets and rocky terrain."
Link to the full article.Very long fun and informative.