Australia used to be a lush jungle and also used to be connected with Antarctica which was also a lush jungle. Moving south messed up the Antarctica side of course, melting glaciers added enough water to turn the big continent into separate islands of Antarctica, Australia, New Guinea, Tasmania, New Zealand and such. One thing that is missing in the animals of Australia is small burrowing animals like ground squirrels (called gophers here in Canada). Australia still has some mole-like marsupials and the giant-sized burrowing wombat but no common squirrel-sized burrowing animal. I figure that deserts are created mostly from ground water levels dropping far enough to not be keeping the ground moist enough for trees. Once the trees are gone, the land gets full sun and dries up fast. The trees also create the humid air to make new clouds that move further inland to keep that ocean-sourced water moving across the continent they are passing over. Only a couple hundred years ago, Argentina (south-east part of South America) used to have much more rain forest like the Amazon basin has but farmers cleared the land to grow crops. Very quickly the land dried up enough to only support cattle and sheep grazing. Now it is even too dry for that in many places. I propose that small burrowing animals in high numbers are needed to keep the water table high by letting rain water soak into the ground. Beavers can also help keep the water from flowing away or the land can be flat like the Amazon basin making water flow slowly and flooding the land often for months. The biggest change that people fear from global warming is sea level rising and flooding 95% of the world's urban areas. The second fear is crop land drying up. Wet soil holds a lot of water so it might be a convenient arrangement to reclaim deserts by raising the water table using beaver-like dams and encouraging ground squirrels and similar animals in grass lands that are too dry for big trees.