The paleofauna of the Eocene Okanagan Highlands consists of Early Eocene arthropods, vertebrates, plus rare nematodes and molluscs found in geological formations of the northwestern North American Eocene Okanagan Highlands. The highlands lake bed series' as a whole are considered one of the great Canadian Lagerstätten. The paleofauna represents that of a late Ypresian upland temperate ecosystem immediately after the Paleocene-Eocene thermal maximum, and before the increased cooling of the middle and late Eocene to Oligocene. The fossiliferous deposits of the region were noted as early as 1873, with small amounts of systematic work happening in the 1880-90s on British Columbian sites, and 1920-30s for Washington sites. Focus and more detailed descriptive work on the Okanagan Highlands site started in the last 1970's. Most of the highlands sites are preserved as compression-impression fossils in "shales", but also includes a rare permineralized biota and an amber biota.
Extent The 1,000 km (620 mi) series of lacustrine deposits are located across the Central British Columbia, Canada southeast to northern central Washington state, United States. grouped informally into "Northern", "Central", and "Southern" sites. The Northern sites consist of unnamed Ootsa Group formations which outcrop as the "Driftwood shales" near Smithers, British Columbia, the "Horsefly shales", of an unnamed formation and unnamed group which outcrop around Horsefly, British Columbia, and possibly sites now considered lost in the Quesnel, British Columbia area, The Central sites represent Kamloops Group formations with the McAbee Fossil Beds, Tranquille River site and Falkland site, all in the Tranquille Formation, the Quichena site and Stump Lake site in the Coldwater Beds and outcrops of the Chu Chua Formation near Barriere, British Columbia. The Southern sites include the Princeton Group Allenby Formation sites surrounding Princeton, British Columbia, such as "Nine Mile Creek", "One Mile Creek", "Pleasant Valley", "Thomas Ranch", "Vermilian Bluffs", and "Whipsaw Creek". The Penticton Groups Kettle River, Marama and Marron Formations in the Boundary District along the Canada-United States border are closely correlated with the Klondike Mountain Formation across the border. The most southerly of the Okanagan Highlands lakes, the Klondike Mountain Formation in Northern Ferry County, Washington include the "Boot Hill site", "Corner Lot site", "Gold Mountain site", "Knob Hill site", and "Mount Elizabeth site". There is debate as to the affiliation of the, potentially lost, Quesnel sites with the Greater Okanagan Highlands. Archibald et al. (2018) in a monograph of the Highlands Hymenoptera families included them as part of the series. However the certainty for the placement was questioned earlier by Eberle et al. (2017) and Archibald and Cannings (2022) who opted to tentatively exclude Quesnel from the highlands while discussing the history of field collecting in the region.
Paleofauna
The Okanagan highlands represent a snapshot of lake, wetlands, and montane forest animal life which existed approximately 15 million years ago after the Cretaceous–Paleogene extinction event. The temperate upland lakes hosted insects, fish, birds, and mammals with the notably well preserved megafossils often retaining insect colour patterns, gnat wing membrane hairs, and whole bird feathers. In some cases the fine detail preservation of soft parts allows for the preservation of internal anatomy. Archibald and Makarkin (2006) suggested the disjunct distribution of genera between the Danish western Limfjord coasts Fur Formation and the Okanagan highlands may have been enabled by rising crust elevations in the northern Atlantic region and subsequent increase in landmass during the Late Paleocene which linked Northern Europe with Greenland until at least the Early Eocene. Several land bridge routes may have acted as migration corridors for biotic interchange, the northern De Geer land bridge from Fennoscandia to North America via northern Greenland, and the southern Thulean land bridge from northern Britain though the Faroe Islands and then Greenland and North America. Several insect genera share disjunct distributions between the highlands and Limfjord including the mecopteran Cimbrophlebia, the giant lacewing Palaeopsychops, the green lacewing Protochrysa, the bull dog ant Ypresiomyrma. The Hat Creek Amber deposits in the central region provide evidence for small and microbiotic elements of the Okanagan Highlands forests though entombed organisms such at terrestrial nematodes and microwasps that otherwise would likely not be preserved in the lake environments. The highlands as a whole have been described as one of the "Great Canadian Lagerstätten" based on the diversity, quality and unique nature of the biotas that are preserved. The highlands temperate biome, preserved across a large transect of lakes, recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines. David Grimaldi et al. (2018) during discussion of inclusions in Alaskan Chickaloon amber, noted the Okanagan Highlands record of latitudinal extinctions, specifically the modern southern hemisphere endemic groups Eomeropidae mecopterans and Myrmeciinae bulldog ants.
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