Paleozoic Era

Paleozoic Era (542 to 251 million years ago)

The massive supercontinent Pangaea formed during the Paleozoic, and this era also saw the diversification and evolution of many of the animal phyla that are still present today. During the Paleozoic:

• The first fish (chordates) appeared more than \(\text{500}\) million years ago, and it is from this common ancestor that vertebrates, including mammals (and humans) are ultimately descended. Fish developed bony spines and jaws with teeth which increased the size and diversity of the prey they could capture.
• Animals with shells and exoskeletons (e.g the trilobites) were in abundance early in the Paleozoic, but declined towards the end of the era.
• The earliest plants colonised land approximately \(\text{430}\) million years ago, having evolved from the nearby algae growing along lakes and other coastal areas.
• Forests of primitive plants covered the Earth's surface, resulting in increased oxygen levels and decreased carbon dioxide levels in the earth's atmosphere.
• The first insects appeared, and later on some species developed wings.
• Later in the Paleozoic amphibians became common and diverse and started moving onto land.
• Early reptiles (synapsids) colonised land.
• Towards the end of the Paleozoic gymnosperms (seed-bearing plants) replaced much of the earlier plant-types.

The end of this period was marked by a mass extinction event (called the Permian-Triassic extinction event) which eliminated almost all marine life but had a less devastating impact on terrestrial species.

South African fossil record: fossils of early land plants such as clubmosses, lycopods, ancestral gymnosperms and algae were found near Grahamstown and Port Alfred. Fossils of plants belonging to the Glossopteris flora are found in the Karoo. This plant flourished throughout the ancient landmass of Gondwanaland. However, by the end of the Permian period this crop had become extinct. The fossilised remains of these plants are found in silts and in rocks throughout the country, where coal deposits can be found (see figure below). Among the organisms that moved on to land at this time were the ammonoids, which are marine invertebrate animals with spiral-shaped shells, the fossils of which are found in the Makhatini flats in KwaZulu Natal.

Map of coal deposits in SA: often these deposits are the sites of plant and animal fossils as they are created by the same process.

"Living fossils" in South Africa: Cycads have been in existence for over 280 million years. There are several rare species of cycads found exclusively within South Africa. They grow very slowly and live for up to a 1000 years. Because they are such a rare species, there are several restrictions on what can be done to them. In South Africa, unless required for conservation purposes, it is illegal to collect, pluck, destroy, export or possess cycads without a special permit.

Cycads have been in existence for over 280 million years.