|Fossil leaf of T. johnsoni|
Tilia johnsoni is an extinct species of flowering plant in the family Malvaceae that, as a member of the genus Tilia , is related to modern lindens (called "limes" in Britain and "basswoods" in the US). The species is known from fossil leaves found in the early Eocene deposits of northern Washington state, United Statesand a similar aged formation in British Columbia, Canada.
Tilia johnsoni leaf fossils have been identified from two locations in the Eocene Okanagan Highlands, the Klondike Mountain Formation near Republic, Washington and at the Quilchena locality near Merritt, British Columbia. Fossil pollen identified as from the genus Tilia has been identified from a greater range of Okanagan Highland fossil sites, having been found in the Allenby Formation near Princeton, British Columbia, at the Falkland fossil site near Falkland, the McAbee Fossil Beds near Kamloops, the Hat Creek Amber and Driftwood Canyon Provincial Park near Smithers. Of the Okanagan Highlands sites, Tilia microfossils and macrofossils have not been identified from the Horsefly fossil beds near the unincorporated community of Horsefly.
The age for the Okanagan Highland locations is uniformly Early Eocene, with the sites that have current uranium-lead or argon–argon radiometric dates being of Ypresian age and corresponding to the Early Eocene Climatic Optimum (EECO). Modern work on the fossil-bearing strata of the Klondike Mountain Formation via radiometrically dating has given an estimated age in the Late Ypresian stage of the early Eocene, betweenat the youngest, and an oldest age estimate of , given based on detrital zircon isotopic data published in 2021. The Quilchena locality is dated to , and is reconstructed as the warmest and wettest of the Early Eocene upland sites from the Okanagan Highlands of British Columbia and northern Washington State.
Tilia johnsoni was described from a single type specimen, a leaf, the holotype being UW 39712, in the paleobotanical collections of Burke Museum, and its counterpart UCMP 9291 in the University of California Museum of Paleontology in California. Working from this specimen, collected in the Republic, Washington area in the early 1980s, the fossil was studied by Jack A. Wolfe of the University of California and Wesley C. Wehr of the Burke Museum.They published their 1987 type description for the species in a United States Geological Survey monograph on the North Eastern Washington dicot fossils. The specific epithet johnsoni is a patronym recognizing the help provided to Wolfe and Wehr by a young Kirk Johnson, now director of the Smithsonian's National Museum of Natural History. Wolfe and Wehr noted that, at the time of publication, T. johnsoni was the oldest macrofossil occurrence for the genus to be described,; older microfossil records of pollen date near to the Paleocene – Eocene boundary, and fruits of an extinct Tilia relative are known from the Eocene of England.
The type leaf of Tilia johnsoni is palmate in venation with an overall orbicular shape, cordate blade base and acute blade tip. The central primary vein is flanked by three pairs of lateral primary veins and the margin of the leaf has evenly spaced, distinctly shaped teeth with rounded sinuses separating them. The inner most set of lateral primary veins run parallel to the median secondary veins, broadly curving upwards and with three secondary veins branching off the exterior side. The branched secondaries run parallel to the next lateral primary vein. The tertiary veins run perpendicular to the secondary veins with an even spacing, while the quaternary veins are orthogonal to the tertiaries forming reticulated pattern of pentagonal and quadrangular spaces.
Formations of the Okanagan Highlands formations represent upland lake systems that were surrounded by a warm temperate ecosystem with nearby volcanism 0.7–1.2 km (0.43–0.75 mi) higher than the coastal forests. This is consistent with the paleoelevation estimates for the lake systems, which range between 1.1–2.9 km (1,100–2,900 m), which is similar to the modern elevation 0.8 km (0.50 mi), but higher.dating from during and just after the early Eocene climatic optimum. The highlands likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable. The paleoforest surrounding the lakes have been described as precursors to the modern temperate broadleaf and mixed forests of Eastern North America and Eastern Asia. Based on the fossil biotas the lakes were higher and cooler then the coeval coastal forests preserved in the Puget Group and Chuckanut Formation of Western Washington, which are described as lowland tropical forest ecosystems. Estimates of the paleoelevation range between
Estimates of the mean annual temperature have been derived from climate leaf analysis multivariate program (CLAMP) analysis of the Republic paleoflora, and leaf margin analysis (LMA) of both paleofloras. The CLAMP results after multiple linear regressions for Republic gave a mean annual temperature of approximately 8.0 °C (46.4 °F), with the LMA giving 9.2 ± 2.0 °C (48.6 ± 3.6 °F). LMA results from Quilchena returned the higher 14.6 ± 4.8 °C (58.3 ± 8.6 °F), slightly higher than seen at Republic, and CLAMP analysis gave an overall mean annual temperature of 13.3 ± 2.1 °C (55.9 ± 3.8 °F). A bioclimatic-based estimate based on modern relatives of the taxa found at each site suggested mean annual temperatures around 13.5 ± 2.2 °C (56.3 ± 4.0 °F) for Republic and 14.7 ± 2.1 °C (58.5 ± 3.8 °F) for Quilchena. These are lower than the mean annual temperature estimates given for the coastal Puget Group, which is estimated to have been between 15–18.6 °C (59.0–65.5 °F). The bioclimactic analysis for Republic and Falkland suggest mean annual precipitation amounts of 115 ± 39 cm (45 ± 15 in) and 121 ± 39 cm (48 ± 15 in) respectively.
The Klondike Mountain Formation is an Early Eocene (Ypresian) geological formation located in the northeast central area of Washington state. The formation is comprised of volcanic rocks in the upper unit and volcanic plus lacustrine (lakebed) sedimentation in the lower unit. the formation is named for the type location designated in 1962, Klondike Mountain northeast of Republic, Washington. The formation is a lagerstätte with exceptionally well-preserved plant and insect fossils has been found, along with fossil epithermal hot springs.
The Coldwater Beds are a geologic formation of the Okanagan Highlands in British Columbia, Canada. They preserve fossils dating back to the Ypresian stage of the Eocene period, or Wasatchian in the NALMA classification.
Langeria is an extinct genus of flowering plants in the family Platanaceae containing the solitary species Langeria magnifica. Langeria is known from fossil leaves found in the early Eocene deposits of northern Washington state, United States and similar aged formations in British Columbia, Canada.
Betula leopoldae is an extinct species of birch in the family Betulaceae. The species is known from fossil leaves, catkins, and inflorescences found in the early Eocene deposits of northern Washington state, United States, and similar aged formations in British Columbia, Canada. The species is placed as basal in Betula, either as a stem group species, or an early divergent species.
Pinus latahensis is an extinct species of conifer in the pine family Pinaceae. The species is known from fossil leaves found in the early Eocene deposits of northern Washington state, United States, and southern British Columbia, Canada.
Comptonia columbiana is an extinct species of sweet fern in the flowering plant family Myricaceae. The species is known from fossil leaves found in the early Eocene deposits of central to southern British Columbia, Canada, plus northern Washington state, United States, and, tentatively, the late Eocene of Southern Idaho and Earliest Oligocene of Oregon, United States.
Amia? hesperia is an extinct species of bony fish in the bowfin family, Amiidae. The species is known from fossils found in the early Eocene deposits of northern Washington state in the United States and southeastern British Columbia. The species is one of eight fish species identified in the Eocene Okanagan Highlands paleofauna.
Barghoornia is an extinct genus of flowering plants in the family Burseraceae containing the solitary species Barghoornia oblongifolia. The species is known from fossil leaves found in the early Eocene deposits of northern Washington state, United States.
Acer spitzi is an extinct maple species in the family Sapindaceae described from a single fossil samara. The species is solely known from the Early Eocene sediments exposed in northeast Washington state, United States. It is the only species belonging to the extinct section Spitza.
Carpinus perryae is an extinct species of hornbeam known from fossil fruits found in the Klondike Mountain Formation deposits of northern Washington state, dated to the early Eocene Ypresian stage. Based on described features, C. perryae is the oldest definite species in the genus Carpinus.
Klondikia is an extinct hymenopteran genus in the ant family Formicidae with a single described species Klondikia whiteae. The species is solely known from the Early Eocene sediments exposed in northeast Washington state, United States. The genus is currently not placed into any ant subfamily, being treated as incertae sedis.
Equisetum similkamense is an extinct horsetail species in the family Equisetaceae described from a group of whole plant fossils including rhizomes, stems, and leaves. The species is known from Ypresian sediments exposed in British Columbia, Canada. It is one of several extinct species placed in the living genus Equisetum.
Fagus langevinii is an extinct species of beech in the family Fagaceae. The species is known from fossil fruits, nuts, pollen, and leaves found in the early Eocene deposits of South central British Columbia, and northern Washington state, United States.
Plecia canadensis is an extinct species of Plecia in the fly family Bibionidae. The species is solely known from Early Eocene sediments exposed in central southern British Columbia. The species is one of twenty bibionid species described from the Eocene Okanagan Highlands paleofauna.
The Eocene Okanagan Highlands or Eocene Okanogan Highlands are a series of Early Eocene geological formations which span a 1,000 km (620 mi) transect of British Columbia, Canada, and Washington state, United States. Known for a highly diverse and detailed plant and animal paleobiota the paleolake beds as a whole are considered one of the great Canadian Lagerstätten. The paleobiota represented are of an upland subtropical to temperate ecosystem series 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 1870–1920s on British Columbian sites, and 1920–1930s for Washington sites. Focus and more detailed descriptive work on the Okanagan Highland sites started in the late 1960s.
Ulmus chuchuanus is an extinct species of flowering plant in the family Ulmaceae related to the modern elms. The species is known from fossil leaves and fruits found in early Eocene sites of northern Washington state, United States and central British Columbia, Canada.
Promastax is a genus of "monkey grasshoppers" belonging to the extinct monotypic family Promastacidae and containing the single species Promastax archaicus. The species is dated to the Early Eocenes Ypresian stage and has only been found at the type locality in east central British Columbia.
Alnus parvifolia is an extinct species of flowering plant in the family Betulaceae related to the modern birches. The species is known from fossil leaves and possible fruits found in early Eocene sites of northern Washington state, United States, and central British Columbia, Canada.
Plecia avus is an extinct species of Plecia in the March fly family Bibionidae and is solely known from Early Eocene sediments exposed in central southern British Columbia. The species is one of twenty bibionid species described from the Eocene Okanagan Highlands.
Polystoechotites is an extinct parataxon of lacewings in the moth lacewing family Ithonidae. The taxon is a collective group for fossil polystechotid giant lacewing species whose genus affiliation is uncertain, but which are distinct enough to identify as segregate species. Polystoechotites species are known from Eocene fossils found in North America and is composed of four named species Polystoechotites barksdalae, Polystoechotites falcatus, Polystoechotites lewisi, and Polystoechotites piperatus, plus two unnamed species. Three of the described species are known from fossils recovered from the Eocene Okanagan Highlands of Washington State, while the fourth is from Colorado.