Silurian to Triassic plant and hexapod clades and their associations: new data, a review, and interpretations

Abstract

A preliminary evaluation of hexapod herbivore damage from selected compression and permineralized biotas from the 220 million-year Late Silurian to Late Triassic interval has revealed many previously unknown patterns of hexapod herbivore use of vascular plants as well as detritivore and predator associations. Data was collected from 48 distinctive hexapod herbivore damage types (DTs) from 21 mostly compression biotas, but with special emphasis on the Rhynie Chert (Early Devonian, ~ 408 Ma), Calhoun Coal (Late Pennsylvanian, ~ 303 Ma) and Molteno Formation (Late Triassic, ~ 226 Ma). These data indicate a two-phase herbivore colonization of land; later expansion of hexapod functional feeding groups (FFGs) initially in the Late Pennsylvanian wetland environments of equatorial Euramerica, and subsequently in Early Permian fluvial systems in the rest of Euramerica, Gondwana, and Cathaysia; the devastating end-Permian extinction; and subsequent rebound of those same FFGs during the ensuing Triassic. Modern-aspect herbivore, detritivore, and predator FFGs are present in Late Pennsylvanian canopied forests, and the full spectrum of all terrestrial FFGs are in place during the Late Triassic. Freshwater FFGs are delayed when compared to the terrestrial record, originating during the Permian, experiencing expansion during the Triassic, and reaching modern levels of all major trophic types during the Late Jurassic. A major conclusion is the omnipresence of convergence in FFGs throughout this interval and the spatiotemporally changing and ephemeral nature of plant hosts and their hexapod herbivore taxa