The ichnogenus Palmiraichnus Roselli for fossil bee cells

Abstract

The ichnogenus Palmiraichnus was erected by Roselli in 1987 to include his formerly described ich‐nospecies castellanosi, and a new one, minor, herein considered a junior synonym of the former. Shape, lining and closure clearly show that these traces are fossil bee cells. Celliforma, the other ichnogenus for non‐clustered fossil bee cells, includes two ichnospecies, bedfordi (=septata) (n. syn.) and pinturensis, which share with Palmiraichnus castellanosi the presence of antechambers and hardened cell walls. This combination of features is characteristic of certain groups of short‐tongued bees and justifies the inclusion of these ichnospecies in Palmiraichnus. Microscopic structures of cell walls and closures are adopted here for ichnotaxonomic purposes and for comparing fossil with extant cells revealing that they are useful ichnotaxobases with respect to the problematic fossil bee cell ichnotaxonomy. The micro‐structure of the cell walls and closures of the three ichnospecies of Palmiraichnus are compared. The presence of antechambers and particularly of the thickened cell rears suggest a relationship between Palmiraichnus castellanosi and Uruguay, an ichno‐taxon also attributable to bees. However, in Uruguay ichnospecies. cells are grouped in well‐defined clusters, whereas in Palmiraichnus castellanosi, cells occur isolated in paleosols, and no intermediate morphologies are known between the two ichnogenera. P. castellanosi, the focus of our study, is also compared with oxaeid cells revealing similarities in size and wall microstructure and differences in microstructure of closures and cell rears.

Key words:

• Trace fossils
• bee cells
• Palmiraichnus
• Celliforma
• late Cretaceous‐early Tertiary
• Uruguay