Glossopteris fossil seed fern leaves from the Permian of Australia. (field of view 12.4 cm across)

Plants are multicellular, photosynthetic eucaryotes. The oldest known land plant body fossils are Silurian in age. Fossil root traces of land plants are known back in the Ordovician. The Devonian was the key time interval during which land plants flourished and Earth experienced its first “greening” of the land. The earliest land plants were small and simple and probably remained close to bodies of water. By the Late Devonian, land plants had evolved large, tree-sized bodies and the first-ever forests appeared.

Glossopteris is probably the most familiar fossil leaf to non-paleobotanists. The name Glossopteris is Latinized from two Greek words meaning “tongue-fern”, referring to the elongated shape of individual leaves. Glossopteris was not a true fern - it was a seed fern, a group of primitive gymnosperms. Glossopteris has been reconstructed as a large deciduous tree.

The Australian rock shown here has several hematite-stained leaf impressions of Glossopteris browniana Brongniart, 1831 (or Glossopteris indica Schimper, 1874 - I’m not sure which one this is). Glossopteris species taxonomy is notoriously convoluted, with >200 nominal species described worldwide. During the Permian, Glossopteris-dominated forests covered much of the ancient continent of Gondwana (= South America + Africa + Arabia + Antarctica + Madagascar + India + Australia).

Glossopteris has tremendous significance in the history of geology. The modern-day geographic distribution pattern of Glossopteris fossils was a key piece of paleontological evidence that Alfred Wegener (1915) used in formulating his Continental Drift Hypothesis, the precursor idea to the Theory of Plate Tectonics. Plate tectonics theory is the # 1 most significant, all-encompassing theory in all of geology.

Classification: Plantae, Pteridospermophyta, Glossopteridopsida, Glossopteridales, Glossopteridaceae

Stratigraphy: hard deltaic claystone, Illawarra Coal Measures, mid-Kazanian or Midian/Tatarian or Dzhulfian Stage, Upper Permian

Locality: Dunedoo area (possibly Lightning Ridge), Sydney Basin, eastern New South Wales, southeastern Australia

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