To be or not to be, that is the question for the nature and proper name for a pair of anterior skull bones in species of the Rhinella granulosa group (Anura: Bufonidae)

Herein we reevaluate the homology and proper name of a set of skull bones in bufonid toads of the Rhinella granulosa species group. Since 2000 these bones have been called prenasals, but a recent publication proposed these bones to be hypertrophied septomaxillae. The first suggestion that these elements represented a new bone in the skull of these toads appeared in the early 1970's, but a formal description and naming did not appear until 1982. We gathered new observations, based primarily on μCT images, of 6 of the 12 known species in the group and present a reinterpretation and alternative description. Although dealing with a single bone present in the skull of a small group of South American toads, for which evidence of monophyly is abundant, may seem unimportant, the relevance of such description may go beyond systematics. Inferring well-based morphological homologies of structures is fundamental for an appropriate understanding of the roles of such structure in the evolution of the group and, consequently, function. In these toads, the area anterior to the nares comprises two bones that, early in development, fuse to the paired septomaxilla, forming an element that protrudes anteriorly to form the distinctive rostral profile of these species. Here we present a redescription of these bones, reevaluate their uniqueness for this group of toads, and discuss the most appropriate name for this element.