The species is dated to the Early Eocenes Ypresian stage and has only been found at the type locality in east central British Columbia.

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.

[1] The genus was not discussed in any depth again until Kevan and Wighton (1981) described a series of orthopteroid fossils from the Paleocene Paskapoo Formation in central Alberta.

[2] Kevan and Wighton identified Promastacoides as a very primitive member of Eumastacoidea and together with Promastax shared a close relationship to the family "Eruciidae".

[5] Promastax archaicus lived in the forests surrounding the Horsefly Shales[1][2] lake system during the Early Eocene Climatic Optimum.

[8] 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 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.

[10] The warm temperate highland floras in association with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents.