I received my PhD from the American Museum of Natural History. I am also a Research Associate at the Natural History Museum of Denmark (Department of Coleoptera), Florida State Collection of Arthropods, The Museum of Entomology, Rancho La Brea Tar Pits and Museum (RLB), as well as the Entomology Section at the Natural History Museum of LA County.
• I focused on the use of insects for paleonvironmental reconstructions, namely insects from the Rancho La Brea Tar Pits (RLB) as paleoclimate indicators for southern California. I applied advances in radiocarbon dating of Quaternary insects in tandem with a novel, higher-resolution climate extraction method to:
• Continue to revise and refine a reconstruction of RLB’s paleoenvironment, and in particular, paleoclimate.
• Establish prevailing conditions in vicinity of RLB during the Quaternary extinction event.
• Help answer questions such as: “To what degree can we predict the possible future climate of California from analogous, prehistoric data?” and “How have the flora and fauna responded to climatic changes over time before and after anthropogenic impacts?”
Ultimately, RLB served as a model system to develop and apply novel methods to study Quaternary insect fauna to global study sites. These developments enrich various lines of research applicable to both paleontologists and neontologists such as biogeography, endemism, ecology, and climate change. Furthermore, these innovations may rejuvenate the discipline of Quaternary entomology as a discipline.
RESEARCH PROJECTS
INSECTS AS PALEOENVIRONMENTAL INDICATORS
Insects are generally adapted to highly specific environmental conditions. Consequently, environmentally sensitive insects can provide useful insights into local ecological conditions. While fossil insects have been well studied at numerous Quaternary and Tertiary sites the world over, they require further exploration at RLB. Fortunately, the life-history and present day climate-restricted geographic distributions for all of the species selected for this study are well documented. Predatory and scavenging species, in particular, which do not rely on a specific food source (e.g., obligate plant host) can migrate independent of flora into suitable habitat as environmental conditions change.
The opportunity to use insects as paleoenvironmental indicators (when confidently identified and with provenance established) exists because most Quaternary, and even many Tertiary, insect species are extant. It is surely plausible to assume that they would have occurred and thrived under the same conditions that they do today. Further, ecological associations of insect species can be traced back for millions of years in some cases, strongly supporting the inference that the ecological requirements of insects identified from the Late Pleistocene in RLB have not changed up to the present. Notably, apart from two scarab beetles that may have specialized on the dung of large and now-extinct mammals, all RLB fossil insects have been identified as extant species.
ACCELERATED MASS SPECTROMETRY RADIOCARBON DATING OF QUATERNARY INSECTS
I use advances in reliable radiocarbon dating (Holden and Southon, 2016) to date a high density of insect fossils for multiple research purposes, namely paleoenvironmental reconstructions. This raises the significance of RLB as a study site because:
• Despite its enduring significance as one of North America’s premier Late Pleistocene localities, there remain critical gaps in our understanding of its biotic history and paleoenvironment. These in turn affect inferences concerning climate, habitat, entrapment events, shifting biological communities, and whether RLB has any significance for understanding larger events, such as the timing and agency of the megafaunal extinctions.
• While RLB is justly famous for its diversity of vertebrates and birds, these species are often insensitive environmental indicators because they are highly mobile or migratory. Other, much more meaningful taxa for purposes of paleoenvironmental reconstruction, such as insects, are under-examined, or have not been collected and interpreted according to modern methods.
• Rigorously studied and dated Late Quaternary paleoenvironmental reconstructions from RLB and the greater Los Angeles Basin are scarce. My research indicates: 1) Quaternary insect remains can be located with great accuracy in radiocarbon time, and 2) well-dated and documented climate indicator beetle species are sensitive proxies for environmental change in the Los Angeles Basin and are valuable for regional comparisons.
Successful methods to radiocarbon dating of Quaternary insects has also revealed wide dating spreads for some deposits, emphasize the lack of biostratigraphy for RLB, challenge inferences based on presumed stratigraphy and/or limited radiocarbon dates, and show the necessity to radiocarbon date each taxon independently.
DIGITAL COLLECTIONS
Please visit my Flickr account (https://www.flickr.com/photos/annarholden/albums) to view albums of insects used for various research projects. Specimens are from RLB, as well as the McKittrick tar pits, both southern California. New material is continuously uploaded and in need of identification. Your help is appreciated!
