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The Glossoperids belong to the family Glossopteridaceae of which no members survive today. Fossils date back to the Permian
(290-248 Ma) and have been located in Australia, South America, Africa, India and Antarctica which indicates that they were a dominant feature of the Gondwanan flora.
There were three key genera in the Glossopterid flora:
Glossopteris: Leaves have a midrib (stranded structure of a number of veins running down the middle of the leaf) and a pattern of meshes on the lamina.
Gangamopteris: Median groove in the leaf but no midrib, the rest as above.
Palæovittaria: No midrib, and only a few cross-connections between lamina veins.
Though there are more genera than these; these are the three most common. Over 200 species of Glossopterids have been described. Since leaf fossils of Glossopterids are seldom attached to any stem, they are hard to classify and placing them into one of the above three groups is often the most simple method.
An
impression fossil of Glossopteris showing a
litter of leaves
It is believed that the Glossopterids grew to about 10 metres in height. Their leaves were arranged in whorls around the stems, and the plants were deciduous which accounts for the large number of fossilised leaves. The height estimation comes from analyses of fossilised wood, which shows similarity to modern-day
Araucaria species.
Glossopterid
leaves featured cross-connections in its venation which is called anastomosing venation and is seen in modern-day dicotyledons. Glossopterid leaves range in size from 1 metre by 1 metre (in the case of
Glossopteris ampla) to much smaller sizes. Their shapes also vary from near-linear to broad-ovate to tongue-shaped. The petioles (leaf-stalks) vary in length, with some species not having any at all.
A fossil of the leaf of a
Glossopterid. [Image: FossilMuseum.net]
Scars along the branches of Glossopterids show where the previous year's leaves were attached. Some of the earliest Glossopterid leaves to appear in the fossil record were found at Bacchus Marsh, Victoria, Australia. The fossils were found in rocks formed by glaciers of the late Carboniferous and early Permian Ice Age and the species were
Gangamopteris angustifolia and G.
cyclopteroides.
It is not clear what Glossopterids descended from, but palaeobotanists suspect that they were derived from an aphlebiate
seed fern of the Carboniferous which lost the pinnate stage of its foliage.
The reproduction of the Glossopterids is important in the evolutionary story, and this is covered next...
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