Promastax
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.
History and classification
The holotype fossil of Promastax archaicus was collected by Lawrence Lambe from outcrops of the Horsefly Shales at the horsefly Mine on 20 July 1906, and then subsequently described by Anton Handlirsch in 1910. The type description was published in his Canadian fossil Insects. 5. Insects from the Tertiary lake deposits of the southern interior of British Columbia, along with a number of other Okanagan Highlands insect species. Handlirsch did not include the etymological derivation of genus or species names in the volume.Handlirsch initially grouped Promastax into the orthopteran superfamily Acridioidea without making a more precise placement. He noted a gross similarity with the Acridinae subfamily as then defined, but that it differed in the venation of the wing apex. The short cubital region he likened to "Mastacinae" genera, but again noted the significant differences within the venation of Promastax archaicus as reason not to place the genus there. The genus was not discussed in any depth again until Kevan and Wighton described a series of orthopteroid fossils from the Paleocene Paskapoo Formation in central Alberta. Along with the monotypic Promastacoides, Promastax was referred by Kevan and Wighton to a new family Promastacidae which they placed in the superfamily Eumastacoidea. Kevan and Wighton identified Promastacoides as a very primitive member of Eumastacoidea and together with Promastax shared a close relationship to the family "Eruciidae". However Promastacoides was subsequently identified as a Susumaniinae stick insect leaving the family Promastacidae with only Promastax. The quality of the characters defined for the erection of Promastacidae were noted as few and of poor quality by Schubnel et al., and they stated that the family should be revised.
Distribution and paleoenvironment
Promastax archaicus lived in the forests surrounding the Horsefly Shales lake system during the Early Eocene Climatic Optimum. The horsefly shales have not been radiometrically dated, but based on shared floral and faunal taxa found in other Early Eocene, Ypresian, age Okanagan Highlands sites, Horsefly is assumed to be contemporaneous. The lake was subject to season summer algal bloom of the diatom Eoseira wilsonii, with the polysaccharide slime grown by E. wilsonii suggested to have enhanced the preservation quality of organisms that were coated with slime films before entombment in the lake bottom.The greater Eocene Okanagan 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 Okanagan Highlands 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 higher than the coastal forests. This is consistent with the paleoelevation estimates for the lake systems, which range between, which is similar to the modern elevation, but higher. Estimates of the mean annual temperature have been derived from leaf margin analysis (LMA) of the Horsefly shales with the LMA returning a mean annual temperature of approximately. The estimated cold month mean temperature during the winter is placed at approximately. These estimates are lower than the mean annual temperature estimates given for the coastal Puget Group, which is estimated to have been between. The bioclimatic analysis for Horsefly suggests a mean annual precipitation amount of.
The Okanagan Highlands fossil sites, which includes the Eocene formations between the Driftwood Shales near Smithers, British Columbia in the north and the Klondike Mountain Formation surrounding Republic, Washington to the south have been described collectively 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 such a large transect of lakes recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines. The warm temperate highland floras in association with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents. This is due to the more seasonally equitable conditions of the Early Eocene, resulting in much lower seasonal temperature shifts. However, the highlands have been compared to the upland ecological islands in the Virunga Mountains within the Albertine Rift of the African rift valley.