Lingulide brachiopods and the trace fossil Lingulichnus from the Triassic of western Canada:: Implications for faunal recovery after the end-Permian mass extinction

The environmental distribution of lingulide brachiopods in western Canadian Triassic marine successions, their relationship with other infaunal organisms occupying the same ecospace, and their role in the aftermath of the Permian-Triassic extinction event is summarized. Western Canada is an ideal location to assess lingulide distribution patterns as upper Paleozoic and lower Mesozoic strata are extensively exposed, and lingulides (cf. Lingularia Biernat and Emig) and the trace fossil Lingulichnus Hakes are both common. A distribution comparison of in situ lingulides and Lingulichnus Hakes with concordantly emplaced lingulide shells and shell beds shows clearly that the latter is a poor indicator of true environmental distribution of these infaunal suspension feeders. Lingulides are rare in uppermost Paleozoic strata in the study area. Most occurrences consist of isolated valves or abraded material in erosional lags. Lingulides remain minor components of infaunal Communities during the earliest Triassic (Griesbachian). Although lingulide valves and valve fragments are the dominant body fossil,Observed, trace fossil analysis indicates that lingulides were minor components of earliest Triassic infaunal communities. Lingulides increase in abundance and importance during the Dienerian and Smithian. Shallow and marginal marine trace-fossil assemblages of this age are dominated commonly by Lingulichnus. Lingulide fossils are less abundant but are found in many shallow and marginal marine lithofacies. Lingulides comprise only a minor component of late Smithian through Anisian infaunal communities. Canadian lingulide abundance reached an acme during the latest Middle Triassic (Ladinian). Fossil material is common in many environments, however, in situ lingulides and the trace fossil Lingulichnus occur primarily in tempestites in proximal offshore through lower shoreface settings and in intertidal flat settings. Although quantitatively more abundant in the Middle Triassic, lingulides were proportionally more abundant in Lower Triassic successions. Regardless of relative changes in abundance, the environmental distribution of lingulides did not differ between Early and Middle Triassic successions. Lingulides comprise only a minor component of Upper Triassic infaunal communities. Early Triassic lingulides did not occupy any environmental settings from which they were excluded prior to the Permian-Triassic extinction or after the postextinction recovery interval. Thus, lingulides were not postextinction disaster taxa but rather were ecological opportunists that dominated some Early Triassic shallow and marginal marine successions.