Celliforma rozeni, a new ichnospecies of bee (Hymenoptera: Anthophila) brood cell from the Eocene of Wyoming

Abstract

Trace fossils of bee brood cells provide direct evidence of nesting behavior in deep time and are particularly valuable where body fossils of bees are rare or absent. The ichnogenus Celliforma Brown represents the principal ichnotaxonomic framework for interpreting fossil brood cells of solitary ground-nesting bees, yet ichnotaxonomic resolution within this group depends critically on the recognition of discrete, behaviorally meaningful constructional characters rather than preservational variation. Here we describe Celliforma rozeni Knecht & Buchmann, isp. nov., from the Early Eocene Wagon Bed Formation of Wyoming, USA. This new ichnospecies is diagnosed by a consistently expressed dextral spiral apical closure composed of seven to eight turns, a feature that exceeds the four to five turns characteristic of the type ichnospecies C. spirifer and falls outside the known range of variation for previously described taxa. The description is based on a holotype and multiple paratypes housed in the Museum of Comparative Zoology, Harvard University, and examined alongside more than 100 additional specimens from the Jerome Rozen Bee Nests Collection (American Museum of Natural History) and private collections. Comparisons of spiral turn number and cell dimensions (apex-base height, maximum width), alongside comparative ichnotaxonomic analysis, support the recognition of C. rozeni as a distinct ichnospecies. A revised key to all five valid ichnospecies of Celliforma is provided. In extant solitary bees, brood-cell closure architecture, including spiral turn number, reflects species-specific and inherited motor programs rather than ontogenetic or environmental variation. Accordingly, C. rozeni is interpreted as a distinct behavioral ichnotaxon, likely representing a separate tracemaker lineage within early Cenozoic ground-nesting bees. The recognition of C. rozeni expands the documented behavioral diversity of Eocene solitary bees and adds resolution to the fossil record of pollinators. The coexistence of multiple Celliforma ichnospecies within Wagon Bed paleosols suggests behavioral differentiation and niche partitioning among ground-nesting bees by the early Cenozoic, underscoring the utility of fine-scale brood-cell architecture for reconstructing pollinator community structure in deep time.