Authors alphabetical list

Imagine you’re sitting in a movie theater. As the film begins, actors’ names flash across the screen. The order of the names is determined by a combination of the actors' contributions to the film and the actors' celebrity status (or contributions to the field of movie-making). When a celebrity stars in a movie, he or she usually gets top billing. But what about when an unknown actor gets the lead role? Or when a celebrity plays a small role? In these situations, the actor may lose out on top billing but be given another place of honor: last billing.
For example, in the original, Marlon Brando and Gene Hackman got top billing for playing Superman’s father and Lex Luthor (respectively) and the then-unknown actor Christopher Reeve received last billing “introducing” him as Superman.
What does this have to do with APA reference style?

The world of scholarly publication is not so different from the movies, at least as far as authorship is concerned. Authors are generally listed in order of contribution to the research, but the last author can also be a contributor of distinction, often the principal investigator. The 6th edition of the Publication Manual recognizes this with the new rule regarding citing sources with more than seven authors in the reference list (section 6.27). The first six authors are listed; all subsequent authors except the last are omitted and replaced with an ellipsis; and then the name of the last author is listed.
Here’s an example of the new reference list style, for a study with 87 authors (yes, 87!):

Terracciano, A., Abdel-Khalek, A. M., Adam, N., Adamovova, L., Ahn, C., Ahn, H.. . . McCrae, R. R. (2005, October 7). National character does not reflect mean personality trait levels in 49 cultures. Science, 310, 96–100. doi:10.1126/science.1117199

In this particular study, after the first author, the authors’ names seem to proceed in alphabetical order . . . until you get to the final author, Robert R. McCrae. Those familiar with the field of personality psychology know that McCrae is one of the leading thinkers in the field (together with Paul T. Costa, Jr., he is responsible for the five-factor personality model).
It won’t always be the case that the last author is someone of distinction, but when it does happen, his or her contributions will be preserved for posterity.