Structural, physiological, and stable carbon isotopic evidence that the enigmatic Paleozoic fossil Prototaxites formed from rolled liverwort mats

Linda E. Graham, Martha E. Cook, David T. Hanson, Kathleen Pigg, James M. Graham

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

New structural, nutritional, and stable carbon isotope data may resolve a long-standing mystery-the biological affinities of the fossil Prototaxites, the largest organism on land during the Late Silurian to Late Devonian (420-370 Ma). The tree trunk-shaped specimens, of varying dimensions but consistent tubular anatomy, first formed prior to vascular plant dominance. Hence, Prototaxites has been proposed to represent giant algae, fungi, or lichens, despite incompatible biochemical and anatomical observations. Our comparative analyses instead indicate that Prototaxites formed from partially degraded, wind-, gravity-, or water-rolled mats of mixotrophic liverworts having fungal and cyanobacterial associates, much like the modern liverwort genus Marchantia. We propose that the fossil body is largely derived from abundant, highly degradation-resistant, tubular rhizoids of marchantioid liverworts, intermixed with tubular microbial elements. Our concept explains previously puzzling fossil features and is consistent with evidence for liverworts and microbial associates in Ordovician-Devonian deposits, extensive ancient and modern marchantioid mats, and modern associations of liverworts with cyanobacteria and diverse types of fungi. Our interpretation indicates that liverworts were important components of Devonian ecosystems, that some macrofossils and microfossils previously attributed to "nematophytes" actually represent remains of ancient liverworts, and that mixotrophy and microbial associations were features of early land plants.

Original languageEnglish (US)
Pages (from-to)268-275
Number of pages8
JournalAmerican Journal of Botany
Volume97
Issue number2
DOIs
StatePublished - Feb 1 2010

Keywords

  • C isotope
  • Liverwort
  • Marchantia
  • Marchantioid
  • Mixotrophy
  • Prototaxites
  • Rhizoid

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics
  • Plant Science

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