The timing of land plant origins
Until now, the first fossil evidence of land plants was from the Devonian era 420 million years ago. However, molecular phylogenetic evidence has suggested an earlier origin in the Cambrian. Strother and Foster describe an assemblage of fossil spores from Ordivician deposits in Australia dating to approximately 480 million years ago (see the Perspective by Gensel). These spores are of intermediate morphology between confirmed land plant spores and earlier forms of uncertain relationship. This finding may help to resolve discrepancies between molecular and fossil data for the timing of land plant origins.
Science, abj2927, this issue p. 792; see also abl5297, p. 736
Abstract
Molecular time trees indicating that embryophytes originated around 500 million years ago (Ma) during the Cambrian are at odds with the record of fossil plants, which first appear in the mid-Silurian almost 80 million years later. This time gap has been attributed to a missing fossil plant record, but that attribution belies the case for fossil spores. Here, we describe a Tremadocian (Early Ordovician, about 480 Ma) assemblage with elements of both Cambrian and younger embryophyte spores that provides a new level of evolutionary continuity between embryophytes and their algal ancestors. This finding suggests that the molecular phylogenetic signal retains a latent evolutionary history of the acquisition of the embryophytic developmental genome, a history that perhaps began during Ediacaran-Cambrian time but was not completed until the mid-Silurian (about 430 Ma).