The integration of ichnofossil and body record in Scarabaeinae (Coleoptera: Scarabaeidae)

M. V. SÁNCHEZ, J. H. LAZA, E. S. BELLOSI, Y J. F. GENISE

Santa Cruz de la Sierra, Bolivia

Congreso; VII Reunión Latinoamericana de Scarabaeidología; 2006

The body fossil record of Scarabaeinae shows that the oldest evidence for Dichotomiina is from the Miocene of Japan, for Canthonina from the Miocene of Kenya, and for Phaneina from the Pleistocene of USA. The ichnofossil record can complete and improve the body fossil record when trace fossils are complex enough to be attributed confidently to particular taxa, as is the case of Scarabaeinae. In sum, the integration of body and ichnofossil records can contribute to the knowledge on the evolutionary history of dung beetles providing more precise minimum ages for the appearance of taxa and behaviors. Fossil brood balls of Scarabaeinae have been known since 1938, and they are very abundant in Cenozoic deposits of southern South America. However, a comprehensive study of these trace fossils, which would enable the possibility of integrating both records, is lacking until now. Seven hundred specimens of fossil brood balls of dung beetles (ichnogenera Coprinisphaera and Quirogaichnus) from Argentinian museums and from our present field research are currently under study. Quirogaichnus, from the Miocene and Pleistocene of Argentina, represents a compound nest resembling those of Canthonina. Different ichnospecies of Coprinisphaera, which are recorded from Argentina (Eocene -Pleistocene), Uruguay (Eocene) and Ecuador (Pleistocene), can be recognized based on the presence and location of the egg chamber. Some fossil balls show a hole that indicates the adult emergence, and no evidence of an egg chamber in the wall, suggesting that it was located inside the provision chamber, like in Canthonina and Dichotomiina. In some of them this hole is open in the middle of a flattened surface. Specimens from which the adult has not emerged preserve remains of the egg chamber showing different morphologies, such as: (1) an inverted cone included in the external, upper, part of the brood ball wall; (2) a cone included in the internal, upper, part of the wall, (3) a spherical chamber included in a mammillated, upper protuberance of the wall, or (4) a secondary and independent smaller chamber connected with the provision chamber by a thin passage. These types of traces are comparable with those constructed by paracoprid Coprini (Dichotomiina and Phanaeina) and Scarabaeini (Canthonina). These data show that the ichnofossil record can predate and complete the body fossil record in about 30-50 m.y. The paleobiological data yielded by these trace fossils are currently under study.