You may include up to 20 authors in a reference list entry.
When an article has more than 20 authors, replace the names prior to the final listed author with an ellipsis, but do not omit the final author:
Davis, Y., Smith, J., Caulfield, F., Pullman, H., Carlisle, J., Donahue, S. D., James, F., O’Donnell, K., Singh, J., Johnson, L., Streefkerk, R., McCombes, S., Corrieri, L., Valck, X., Baldwin, F. M., Lorde, J., Wardell, K., Lao, W., Yang, P., . . . O’Brien, T. (2012).