The Fossil History of Australia

Paleozoic Era - Cambrian Period

(from the old Welsh word for Wales)

(590 to 506 million years ago)

This period delights fossil collectors from all over the world.

he Earth became warmer, and Australia was just north of the equator during this time. Organisms with hard shells, invertebrates, developed in large numbers and remains of these are found in abundance today. Towards the end of the Cambrian time, animals with backbones, called vertebrates, also began to appear.

The sea contained all known life during this period, and the most prolific invertebrate species of the Cambrian era is the trilobite, which was normally a small animal up to about 10cm (4in) long, with the largest being around 60 cm (24in). There are many types of trilobite, and these may relate to particular time zones within the Cambrian era. When remains of a known trilobite are found, this information is used to help date that area.

A trilobite is divided into three parts, being the centre lobe and two pleural lobes. It also has three main segments, the cephalon (head section), thorax, and pygidium, (tail section). The flexible thorax had up to 50 segments. As the trilobite matured, it shed its outer shell numerous times, and, with the right conditions, each of these shells could have become fossilized.

There are many varieties of trilobite which are uniquely found in Australia, such as the asthenopsis queenslandica which has a fourteen section thorax.

Another main invertebrate life form was the brachiopod, which was an animal whose soft part was covered by a double shell, also called a valve. These have relatives living today, unlike the archeocyathids, which lived in a cone shaped walls, and which evolved and became extinct within the Cambrian time. Fossils of archeocyathids are found in the Flinders Ranges in South Australia.

Vertebrates appeared during the later part of the Cambrian time. Clues to the development of the vertebrates as fragments of primitive fish with a simple tail fin but no moveable jaw. Fish, as we know them today, did not develop until much later.

The enormous numbers of fossils from this period indicate a huge explosion of life all over the Earth with many new species from this period still to be defined.

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