Major Paleozoic land plant evolutionary bio-events

Abstract

Adaptive radiations and extinctions affecting tracheophytes, the only group of land plants with a well-documented fossil record, occur during time intervals distinct from those affecting marine invertibrates. This distinctive pattern is recognizable at both Era and Period levels. Discordance between tracheophyte appearance, diversification and extinction and contemporary marine bio-events has been reflected in the recognition of ‘planetary’ floras (Palaeophytic, Mesophytic, Cenophytic), the counterparts of marine invertibrate-based Eras of the Planerozoic (Paleozoic, Mesozoic, Cenozoic). Some have recognized significant levels of land-plant evolution, Epochs, within these planetary floras. With the discovery in the past 20 years of a major group of Middle Ordovician/Lower Silurian post-algal/pre-tracheophytic land plants, the concept of the Palaeophytic and its Epochs must be redefined. Here, the redefined Palaeophytic extends from the mid-Permian downward into the mid-Ordovician and three ‘evolutionary land floras’ are recognized: Eoembryophytic (mid-Ordovician to pre-latest Early Silurian); Eotracheophytic (latest Early Silurian through early Gedinnian); and Eutracheophytic (late Gedinnian to mid-Permian). The Silurian/Devonian boundary stressed in prevous Palaeophytic subdivisions is considered of limited importance as a major benchmark in land plant evolution. A newly defined Era, the Epeirophytic, a continental counterpart of Kryshtofovich's marine Thalassophytic, is recognized with an upper boundary at the mid-Ordovician and extending down indefinitely into the Precambrian. One major evolutionary flora, the Phycomycophytic, first recognized by Kryshtofovich for the Thalassophytic, is recognized for the continental habitat as well.