Massive volcanic eruptions at the Permian would have created massive selection pressure to survive in a world full of ash, with reduced oxygen available, and with a devastated landscape containing much less food. Many species would have lacked these abilities and gone extinct. The formation of Pangea would have greatly reduced coastline/shallow salt water habitat, eliminating area and ecological niches
Work Step by Step
Review the chapter and think about what leads to extinction of organisms. Then try to match it up with ecological shifts (volcanoes) and loss of habitat (Pangea forms) as mentioned in the question.