Seniority is determined by length of terms. If members started on the same day, they are ranked alphabetically by last name
Says I cannot include links because I don't have 20 posts but it was on wikipedia's article listing House members by seniority.
My name is close to the beginning of the alphabet, lucky me. Assuming of course, they decided not to trash protocol and start from z. Personally, I prefer the "pick a number 1-10" method