Glossopteris

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Glossopteris (Greek glossa, meaning "tongue", because the leaves were tongue-shaped) is the largest and best-known genus of the extincthi order of seed ferns known as Glossopteridales. Long considered a fern after its discovery in 1824, it was later assigned to the gymnosperms. The genus is placed in the division Pteridospermatophyta.

Glossopteris was a woody, seed-bearing shrub or tree, 4-6 m in height. They had a softwood interior that resembles conifers of the family Araucariaceae. Seeds and pollen-containing organs were borne in clusters at the tips of slender stalks attached to the leaves. Still, some species may have borne seeds in cone-like structures. They are believed to have grown in very wet soil conditions, similar to the modern Bald Cypress. The leaves could exceed 30 cm in length.

The Glossopteridales arose during the Permian on the great southern continent of Gondwana. These plants went on to become a dominant part of the southern flora through the rest of the Permian and early Triassic periods, though they dwindled to extinction by the end of the Triassic.

Glossopteris tapered upwards like a Christmas tree. Instead of needles, they had large, broad lance- or tongue-shaped leaves that fell to the ground at the end of summer. It is unknown if the leaves turned colors, but it seems likely. The fossilized tree rings in the Glossopteris trees reveal that they grew steadily each summer and abruptly stopped for winter.

More than 70 fossil species of this genus have been recognized in India alone, with additional species from South America, Australia, Africa, and Antarctica. Only a few fossils from the northern hemisphere have been considered as members of this group, but these are not identified with great certainty.

Glossopteris fossils are surprisingly homogeneous and are distributed throughout the southern hemisphere. Twenty species of leaves found in Antarctica are common in the rocks of similar geologic age in India, located north of the equator and half a world away. Seeds, much too large to be windborne, could not have blown across thousands of miles of open sea, nor could they have floated across vast oceans. Facts such as these led the Austrian geologist Eduard Suess to deduce that there had once been a land bridge between these areas. He named this large land mass Gondwanaland (named after the district in India where the plant Glossopteris was found). These same facts would also lend support to Alfred Wegener's Continental drift theory.

[edit] References

• Davis, Paul and Kenrick, Paul; Fossil Plants. Smithsonian Books (in association with the Natural History Museum of London), Washington, D.C. (2004). ISBN 1-58834-156-9