An overview of hymenopteran cocoons as a tool to interpret ichnospecies of Fictovichnus (Pallichnidae) and other fossil cocoons of wasps

GENISE, J. F.; SARZETTI, L. C; MOLINA, A.; SARZETTI, L. C; MOLINA, A.; DINGHI, P,A.; DINGHI, P,A.; GENISE, J. F.

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Año: 2019 vol. 34 p. 562 - 574

0883-1351

Hymenopteran cocoons are complex structures constructed from silk by larvae and exhibit a wide rangeof morphologies, compositions, and textures. The recognition of the most relevant characters of modern cocoons isimportant for the accurate identification of trace fossils attributed to wasps, which are included in the ichnogenusFictovichnus. Characters assessed in this study are length, equatorial diameter, diameters near the extremes, shape,color, texture, surface morphology, and occurrence (isolated or clustered). We mapped these characters onto ahymenopteran phylogeny, revealing that the distribution of most of them has no evident phylogenetic signal. In manycases, there is more than one character state in a single family, whereas others appear distributed among severalgroups. Ellipsoidal and ovoid cocoons, showing membranous texture are the most basal and common characters.Bilobated, subconical and fusiform shapes, clustering, nipple and pores seem to be autapomorphies for certain groups.Crabronidae, Pompilidae, Scolioidea and Thynnoidea construct hard coriaceous cocoons, which may show distinctivesurface morphologies and would have the highest preservation potential in paleosols. Data presented herein show thatboth Fictovichnus sciuttoi and Fictovichnus aragon were correctly attributed to Crabronidae or Pompilidae, althoughScolioidea and Thynnoidea cannot be ruled out because of the shape and coriaceous texture of their cocoons.According to the low phylogenetic signal of Hymenoptera cocoons found herein, it would be impossible to refine theaffinities of these ichnospecies to particular taxa. The simple morphology of Fictovichnus gobiensis precludes adefinitive attribution, either to wasps or to coleopterans, even after the new data presented herein.