Key to Pheidole crassicornis group

This worker key is based on:

This compact assemblage of medium-sized species is an apparent monophyletic offshoot from a common ancestor with the fallax group, or else a derivative phylad within it. It shares the same basic head and body form, as well as the same general pattern of rugoreticulate sculpturing, as members of the fallax group. Its distinguishing features are the flattened basal portion of the antennal scape and consistently broad occiput of the minor worker (a slight deviation in the latter character occurs in Pheidole erethizon and Pheidole guerrerana). All of the known crassicornis-group species are Nearctic, ranging among themselves variously from the southeastern United States to the southern reaches of the Mexican Plateau. (Two Neotropical species, Pheidole claviscapa, placed in the fallax group, and Pheidole laticornis, placed in the diligens group, also have broadened scapes but are excluded from the crassicornis group because their minor workers have narrowed occiputs with well-developed posterior nuchal collars. Three other species placed here in the crassicornis, namely erethizon, Pheidole fariasana, guerrerana, and Pheidole spathicornis, may belong phylogenetically in the fallax group, as evidenced by the head shape and sculpture of the major caste. In other words, the basal flattening of the scape may be a trait subject to easy convergence.

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 * Occiput of major and minor smooth, carinulate, or foveolate, not rugoreticulate . . . . . 2