The arrangement of the orders pretty much follows George Gaylord Simpson’s classic “Principles of Classification and a Classification of Mammals” (Simpson, 1945) which was the basic textbook system up until the end of the last century. The apparent alphabetic disorganization is created by un-included (for simplification) of higher levels of classification that represent degrees of relatedness, such as infraclass and subclass which link various orders together. That said this table is now well out of date and I will put updating it on the top of my to do list.