Ordovician land plants and fungi from Douglas Dam, Tennessee

Abstract

Ordovician land plants have long been suspected from indirect evidence of fossil spores, plant fragments, carbon isotopic studies, and paleosols, but now can be visualized from plant compressions in a Middle Ordovician (Darriwilian or 460 Ma) sinkhole at Douglas Dam, Tennessee, U. S. A. Five bryophyte clades and two fungal clades are represented: hornwort (Casterlorum crispum, new form genus and species), liverwort (Cestites mirabilis Caster & Brooks), balloonwort (Janegraya sibylla, new form genus and species), peat moss (Dollyphyton boucotii, new form genus and species), harsh moss (Edwardsiphyton ovatum, new form genus and species), endomycorrhiza (Palaeoglomus strotheri, new species) and lichen (Prototaxites honeggeri, new species). The Douglas Dam Lagerstätte is a benchmark assemblage of early plants and fungi on land. Ordovician plant diversity now supports the idea that life on land had increased terrestrial weathering to induce the Great Ordovician Biodiversification Event in the sea and latest Ordovician (Hirnantian) glaciation.

A Subsurface Stepping Stone Hypothesis for the Conquest of Land by Arthropods

“…Finding supporting fossil evidence for our hypothesis is not easy, as Paleozoic arthropod fossils in caves are rare [85,86], and Paleozoic caves are not well preserved [77,78,87]. The lack of fossilization of cave fauna is demonstrated by the isopod suborder Phreatoicoidea, which is currently exclusive to caves, but whose fossils are commonly found in late Carboniferous marine sediments.…”

A eurypterid trackway from the Middle Ordovician of New York State

“…The chasmataspidid Hoplitaspis Lamsdell, Gunderson, and Meyer, 2019 was large enough, but it had a swimming paddle, which should be reflected in the trackway morphology. Putative Chasmataspis Caster and Brooks, 1956 (see Dunlop et al, 2004) trackways (Retallack, 2020, fig. 3a, b) resemble Palmichnium antarcticum with series subparallel to the midline, although their terrestrial capabilities are unknown.…”

Fossil soils: trace fossils of ecosystems on land and windows on the context of evolution

“…Cambrian and Ordovician soils contain abundant liverwort-like spores (p. 164). Retallack (2019b) finally found 460 million year-old fossil liverworts, hornworts, mosses, lichens, and mycorrhizae in Tennessee (p. 164): nonvascular plants had indeed colonized the land.…”