Fossil palm beetles refine upland winter temperatures in the Early Eocene Climatic Optimum

Abstract

Eocene climate and associated biotic patterns provide an analog system to understand their modern interactions. The relationship between mean annual temperatures and winter temperaturestemperature seasonality-may be an important factor in this dynamic. Fossils of frost-intolerant palms imply low Eocene temperature seasonality into high latitudes, constraining average winter temperatures there to >8°C. However, their presence in a paleocommunity may be obscured by taphonomic and identification factors for macrofossils and pollen. We circumvented these problems by establishing the presence of obligate palm-feeding beetles (Chrysomelidae: Pachymerina) at three localities (a fourth, tentatively) in microthermal to lower mesothermal Early Eocene upland communities in Washington and British Columbia. This provides support for warmer winter Eocene climates extending northward into cooler Canadian uplands.palm bruchines | paleoclimate | Okanagan Highlands | palm pollen

Dispersal of thermophilic beetles across the intercontinental Arctic forest belt during the early Eocene

“…Far more frequently, at least as reported in the literature, extant boreotropical relicts show divergences into New and Old World lineages before (Paleocene 25 ) and after (late Eocene 26 – 28 ) the early Eocene, and their distributions are probably constrained by mild winter temperatures, as in the palms 29 . At the Eocene-Oligocene boundary, winter temperatures decreased, were more different from summer temperatures and became less constant between years 2 , coincident with New-Old World divergences in swallowtail butterflies 26 , tropical ferns 28 and the plums ( Prunus ) 27 ; the former dispersing southward at this time, possibly with frost-intolerant host plants that were gradually replaced by a more temperate flora.…”

A review of paleobotanical studies of the Early Eocene Okanagan (Okanogan) Highlands floras of British Columbia, Canada, and Washington, USA

“…The McAbee fossil beds are also known for their abundant and well-preserved insect fossils (Douglas and Stockey 1996;Archibald et al 2010Archibald et al , 2013Archibald et al , 2014Archibald and Bradler 2015).…”

“…The region of the Eocene Okanagan Highlands is significant because its rich flora and insect and fish faunas document the biota of higher elevation sites around the time of the Early Eocene Climatic Optimum, about 52-50 Ma Zachos et al 2008;Archibald et al 2011Archibald et al , 2014Smith et al 2010Smith et al , 2012. Coastal assemblages of similar age include many tropical to subtropical elements that grew under warm climates (Rouse 1962;Mustard and Rouse 1994).…”

Diptera of the middle Eocene Kishenehn Formation. I. Documentation of diversity at the family level

“…There are 54 additional taxa with family rank that are extinct (Nagatomi and Yang, 1998;Poinar, 2010;Pape et al, 2011;Zhang et al, 2011;Zhang, 2012). In North America, the Eocene Florissant, Green River and Okanagan/Republic Lager-stätten have, to date, produced described species in 36, 26 and 15 families, respectively (Table 2) (Rice, 1959;Wilson, 1977Wilson, , 1978Douglas and Stockey, 1996;Wehr andBarksdale, 1996, 1998;Meyer, 2003;Archibald, 2007;Archibald et al, 2010Archibald et al, , 2013Archibald et al, , 2014aArchibald et al, , 2014b. For reference, Baltic amber has produced described species in 81 dipteran families, only one of which, Hoffeinsmyiidae, is extinct (Michelsen, 2009;EDNA, 2017).…”