A fossil-informed pattern of body size increase and local extinction in <i>Basiceros</i> dirt ants (Hymenoptera: Formicidae)

<i>Basiceros</i> dirt ants are morphologically distinct and widely distributed members of Neotropical communities. These ants possess features that aid in leaf litter camouflage and are larger than other closely related lineages with similar cryptic adaptations. Here, we report the first fossil of this genus group, <i>Basiceros enana</i> sp. nov., from Miocene-aged Dominican amber, which reveals a pattern of body size evolution and disjunct biogeography. The fossil evidences the local extinction of <i>Basiceros</i> in the Caribbean, even as living <i>Basiceros</i> are known from Honduras to Southern Brazil. Using combined morphological and molecular datasets of all closely related lineages, we recover the evolutionary trajectory for body size within the group, demonstrating that body size was initially small in these ants and followed by a rapid expansion of body size in the common ancestor of all living species. Results reflect the capacity for early morphological evolution to influence perceived patterns of body size increase through a mosaic of ancestral legacy and continuous enlargement.