Since the planet is designed to support our kind of life, look to analogous regions of our own planet. The Serengeti plain was mentioned as a possible source.
Species from the same general area will share many of the same characterisitcs. Australia, for example, has kangaroos, but they aren't the only marsupials to be found there. We didn't have just one kind of dinosaur, we had hundreds. At the same time, the fact that there are only two land masses will lessen the diversity of life on the planet, as isolated pockets are required to support pockets of diversity.
The weather pattern inside the continent will be very cold winters and hot summers. The volcano's existence will imply very fertile ground around it, which would support large grasslands, and large herds of animals.
There are many possible paths for evolution to take in an environment like this. An example is the Brittle Star, a starfish whose entire skin is light-sensitive and is used in place of eyes.
One of the major qualities of ecologocal niches is that they don't abruptly transit from one to another. Rainforest doesn't abruptly end and the desert begin. There's a scrub forest, then grasslands, and then the desert.