Glossopteris: The Fossil Plant That Helped Reveal Gondwana

Glossopteris was a group of extinct seed plants that dominated the forests of the southern continents during the Permian Period, about 299 to 252 million years ago. Its fossil leaves are found in South America, Africa, India, Australia and Antarctica, lands now separated by thousands of kilometres of ocean. This remarkable distribution made Glossopteris one of the key pieces of evidence that the southern continents were once joined in a single landmass, Gondwana, and later helped convince geologists that continents move.

What Glossopteris was

The name Glossopteris means “tongue fern”, from the Greek glossa (tongue) and pteris (fern). It was given in 1828 by the French botanist Adolphe Brongniart, one of the founders of palaeobotany, because the leaves are tongue- or spoon-shaped. Despite the name, Glossopteris was not a fern but a gymnosperm, a seed-producing plant.

The leaves have a strong central midrib and a fine network of veins, which makes them easy to recognise. Seeds and pollen organs were attached to the leaves in a distinctive way, and botanists still debate how they were arranged. Some researchers have suggested that glossopterids were related to the ancestors of flowering plants, but this remains uncertain.

Many glossopterids were trees. Fossil trunks show annual growth rings, and some probably grew 20 metres or more tall. Their roots, known from fossils called Vertebraria, had a distinctive segmented look and contained air spaces that helped them survive in waterlogged soils. The trees appear to have been deciduous, shedding their leaves seasonally, which suited the long polar winters of the high southern latitudes where many grew.

Forests and coal of the south

During the Permian, Glossopteris forests covered huge areas of Gondwana, the southern part of the supercontinent Pangaea. As the late Paleozoic ice age came to an end, these forests spread across swampy lowlands left by retreating glaciers.

Their remains formed thick coal seams, much as the Carboniferous coal forests had done earlier in the northern tropics. The Permian coalfields of India’s Damodar Valley, the Sydney and Bowen basins of Australia and the Karoo Basin of South Africa are largely built from glossopterid plants. In India the rock sequence containing these coals is called the Gondwana System, and it gave its name to the whole supercontinent.

From Gondwanaland to continental drift

Land bridges

In the 19th century, geologists noticed that the same plant fossils, now called the Glossopteris flora, appeared in India, southern Africa, South America and Australia. The Austrian geologist Eduard Suess proposed the name “Gondwanaland” in the 1880s for a former southern landmass, after the Gondwana region of central India, meaning “forest of the Gonds”.

Suess and most of his contemporaries assumed that the continents had always been in roughly the same places. To explain the shared fossils, they suggested that land bridges had once linked them and later sank beneath the oceans.

Wegener and du Toit

Alfred Wegener, who proposed continental drift in 1912, used the Glossopteris flora as part of his case. He argued that the plants were best explained if the southern continents had been joined together and had since drifted apart, rather than connected by vanished land bridges.

The South African geologist Alexander du Toit made the evidence much stronger. In his book Our Wandering Continents (1937) he showed in detail how rock sequences, glacial deposits and fossils, including Glossopteris, matched across South America and southern Africa. Because the seeds of Glossopteris were relatively large and heavy, it was unlikely that wind or sea currents had carried them across oceans.

Antarctica and Scott’s last expedition

Antarctica provided one of the most dramatic chapters in the Glossopteris story. On the return journey from the South Pole in February 1912, Robert Falcon Scott’s polar party collected rock samples from the Beardmore Glacier area, near Mount Buckley. They carried about 16 kilograms (35 pounds) of specimens to their final camp, where they died in March 1912.

A search party found their tent and the specimens in November 1912. When the rocks reached Britain, the palaeobotanist Albert Seward identified Glossopteris among them. The discovery confirmed that Antarctica had once had a much warmer climate, with forests, and that it shared its flora with the other southern continents.

Later expeditions found many more glossopterid fossils in Antarctica, including fossil forests with tree stumps still in growth position in the Transantarctic Mountains. In the late 1960s, the discovery in Antarctica of the Triassic land reptile Lystrosaurus, already known from southern Africa and India, further supported the idea of a united Gondwana.

Forests near the pole

The Antarctic fossil forests raise a striking question. During the Permian, much of Antarctica lay at high southern latitudes, roughly where it is today, so the trees grew in a world of months-long summer daylight and months-long winter darkness. No forests grow at such latitudes now.

Glossopteris appears to have coped by growing quickly during the bright summers and shedding its leaves before winter. Growth rings in fossil wood, often wide and sharply bounded, record this strong seasonal rhythm. Fossil leaf mats, layers of fallen leaves pressed together, are thought to represent autumn leaf fall. These forests show that the Permian world, after the ice age ended, was warm enough for trees to thrive close to the South Pole.

By the numbers

Extinction

Glossopteris largely vanished at the end of the Permian, about 252 million years ago, during the Permian–Triassic extinction, the largest mass extinction in Earth’s history. Its disappearance is one of the clearest signals of the crisis on land in the southern continents. In the Triassic, the forests of Gondwana were dominated by a different group of seed plants, the seed fern Dicroidium.

Myths and facts

Glossopteris is often described as a fern because of its name. In fact it was a seed plant and reproduced by seeds, not spores.

It is also sometimes said that Glossopteris alone proved continental drift. It was an important clue, but it worked together with many other lines of evidence: the fit of the coastlines, matching rocks and glacial deposits, and other fossils such as Mesosaurus and Lystrosaurus. Proof that continents move came only with plate tectonics in the 1960s.

Timeline

• c. 299 million years ago: The Permian begins and Glossopteris spreads across Gondwana as the ice age wanes.
• c. 252 million years ago: Glossopteris largely disappears in the Permian–Triassic extinction.
• 1828: Adolphe Brongniart names Glossopteris.
• 1880s: Eduard Suess names Gondwanaland, partly on the evidence of the Glossopteris flora.
• 1912, February: Scott’s polar party collects Glossopteris-bearing rocks near the Beardmore Glacier.
• 1912, November: The specimens are found with the bodies of Scott’s party.
• 1937: Alexander du Toit sets out the southern evidence in Our Wandering Continents.
• 1960s: Plate tectonics confirms that the continents of Gondwana drifted apart.

Why it matters

Glossopteris is one of the most famous fossils in the history of geology. Its presence on every southern continent, including frozen Antarctica, helped reveal the former supercontinent of Gondwana and made the case for continental drift. It also built the Permian coal deposits of India, Australia and southern Africa that are still mined today.