An interesting timeline, indeed.
I would like to expand upon in slightly more detail some of the adaptions previously mentioned.
Photosynthetic symbiosis: this could take several forms. Outright adaption of the skin to become more light sensitive and reactive, symbiotic adaptions with plant life to enable conversion of light to bio-energy, or a psionic power which accomplishes the same thing.
Light or heat to bio-electrical conversion: in species already winged with transparent membranes or materials, the wings could potentially adapt to convert light directly into bio-electricity. This particular adaption would be unlikely except to insectoid species as their wings already tend to fragment light. Again a unique psionic power might also suffice. Furthermore, as many species can adapt to living near volcanic vents without traditional light at all, there is no reason that Athasian species could not do the same, drawing their nutrients from an ecology surround a vent, possibly even converting heat to bio-energy instead of light.
Parthenogenetic reproduction: common to simpler life forms, however even the occasional complex life form can manage it in extreme or unusual circumstances. Athas qualifies. However, such reproduction seldom leads to generic diversity, even if it manages to sustain and perpetuate the species.
Elemental adaptions: Athas is effectively a combination of the elemental planes of earth and fire. Given the possibilities of psionics, and other methods of elemental bloodlines, having entire groups or even partial species conversion to an elemental nature would be a survival tactic.
Possible hybridization of species: in order to perpetuate and survive, some species might resort to extra-species liaisons. With psionics to smooth the way, it becomes possible at least, though for sentient species there remains the moral and ethical concerns. Dragons, at least those on other worlds, seem to do so with great regularity, if without any cultural or religious explanation being provided.
Symbiotic adaption of species: a more likely evolutionary scenario than hybridization, the physical or societal symbiosis of multiple species is an adaption of great likelihood on Athas. Some have already been mentioned: group minds, simple psionic linkages between disparate species to aid one another, plant-animal symbiosis, and so forth. Symbiosis with more exotic entities is also possible: elementals, ethereal, ghosts, vestiges... Some might even attempt to switch to negative energy to survive, though this last would effectively be much the same as a defiler.