Holden, Anna , Erwin, Diane M. , Schick, Katherine , Gross, Joyce , Hall, Justin .
Traces in asphalt: New observations of Pleistocene plant – insect interactions from the Rancho La Brea Tar Pits, Los Angeles, California, USA.
The fossil record continues to reveal new information about the intricate interrelationships and usage of plants by phytophagous insects, and the antiquity of these associations. Sites where fossil plants and whole-body insects co-occur are relatively rare; the insect remains typically limited to isolated wings and the number of specimens recovered relatively low. Nontheless, an insect’s presence can be established through study of e.g., insect-induced galls, distinctive feeding traces on leaves and stems, and as we report here leaf-cutter bee nest cells constructed of plants growing near nesting sites. Much of the fossil evidence for these associations however come from the study of two-dimensional traces on fossil leaf compressions. Recent investigation of Rancho La Brea Tar Pit (RLB) collections, arguably the world’s richest late Pleistocene deposit, has yielded an array of identifiable insect mediated trace fossils ranging from ~11,000 – 60,000 radiocarbon years BP. Because the geologically young RLB fossils are original, asphalt-impregnated, and three-dimensional, their complex structural detail allows comparison to extant taxa. Recognized thus far are Juniperus twigs with galleries attributable to the families Curculionidae and Buprestidae (both Coleoptera). Beetles in both families are known to colonize trees weakened by environmental stress such as drought, fire, and intense vegetation competition or water table changes. The distinct curculionid galleries narrow down the makers to three species of Phloeosinus (Scolytinae) and infer the presence of two juniper species. Radiographs of two leaf-cutter bee nest cells reveal intact pupae. The diagnostic circular and oval-shaped leaf cutouts used to line the cells are attributable to the genus Megachile (Hymenoptera: Megachilidae). That at least three different plant species were used in cell construction allows us to investigate plant associations available at time of nest building. Although fossil insect nests have been reported as far back as the Cretaceous, this is the first report of Megachile from the Pleistocene and first record of fossil nests with pupae. In addition, a number of fossil oak galls have been identified and attributed to gallwasps (Hymenoptera: Cynipidae). Cynipids are tiny stingless wasps the majority of which gall specific oak hosts inducing wasp-specific gall morphologies complex enough to be diagnosed to species. The RLB beetle galleries, nest cells, and galls represent new records for the Pleistocene and this region of the southwestern US. The combination of both insect and plant habitat requirements offer a powerful tool for better understanding Rancho La Brea's Pleistocene environment.
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1 - Natural History Museum of Los Angeles County, Department of Entomology, 900 Exposition Boulevard, Los Angeles, CA, 90007, USA
2 - University of California, Museum of Paleontology, 1101 Valley Life Sciences Building, Berkeley, CA, 94720, USA
3 - University of California, Essig Museum of Entomology, 1101 Valley Life Sciences Building, Berkeley, CA, 94720, USA
4 - University of California, Berkeley Natural History Museums, 1101 Valley Life Sciences Building, Berkeley, CA, 94720, USA
5 - Natural History Museum of Los Angeles County, Dinosaur Institute, 900 Exposition Boulevard, Los Angeles, CA, 90007, USA
Rancho La Brea Tar Pits
bee nest cells.
Presentation Type: Poster:Posters for Sections
Location: Grand Salon A - D/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 5:30 PM
Candidate for Awards:None