FACT
Hard shells fossilise
more readily than
soft bodied
organisms, as they
are better at
resisting decay, take
significantly longer
to break down, and
have a greater
chance of surviving
burial under layers
of sediment. For this
reason, hard-shelled
organisms such as
trilobites dominate
the fossil record.
Sometimes by pure
luck, geologists find
beautiful fossils of
soft bodied
creatures. A good
place for
discovering softer
bodied organisms is
the Burgess Shale
site.
Paleozoic era (542 to 251 million years ago) DUMMY
Themassive 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 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 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, ances-
tral gymnosperms and algae were found near Grahamstown and Port Alfred. Fossils of plants
belonging to theGlossopterisflora 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 (Figure 11.8). Among the
organisms that moved on to land at this time were the ammonoids, which are marine inver-
tebrate animals with spiral-shaped shells, the fossils of which are found in the Makhatini flats
in KwaZulu Natal.326 11.3. Life’s History