How do the ashtanga poses differ from those of other yoga systems?
Well, there aren’t really any “ashtanga poses”. Sometimes students coming from tamer class styles assume that some of the arm balances or other things they haven’t been exposed to are unique to ashtanga but (with a few weird exceptions in the advanced series work) all the poses are also present in other yoga systems. Sometimes the names of the poses differ and frequently there are minor variations not shared by, say, Iyengar or anusara style yogis. What is unique to ashtanga is the routining of the various series, the pace of the practice, and the various vinyasa sequences used to enter and exit the poses.