Shared first authorship

In most scientific communities, the order of author names on a publication serves to assign credit and responsibility. Unless authors are presented in alphabetical order, it is assumed that the first author contributes the most and the last author is the driving force, both intellectually and financially, behind the research. Many, but not all, journals individually delineate what it means to be a contributing author and the nature of each author's role. But what does this mean when a paper has co-first authors? How are academic librarians going to handle questions surrounding co-first authorship in an era in which author metrics are important for career advancement and tenure? In this commentary, the authors look at the growing trend of co-first authorship and what this means for database searchers.