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Open University
S193_1 12 Hours
Introductory
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Course Description
The Palaeozoic Era was a very important time in
the history of life. Using evidence from fossils, we start by looking at
the Cambrian explosion, when many forms of animal life first appeared
about 545 million years ago. Then we move on to study creatures living
in the Ordovician seas, including the extinct trilobites. Next, we'll
investigate the invasion of land by plants and invertebrates that
occurred in the Silurian Period, and look at life in Silurian seas.
You'll also learn about the Devonian Period, when vertebrates first
moved onto land. The unit finishes with a brief outline of vertebrate
evolution.
This unit is modified from the Open
University Level 1 course S193; Fossils and the History of Life.
For this part of that course, students are also given two replicas of
Palaeozoic fossils to develop the skill of making and recording
observations on three-dimensional specimens. Reference to studying these
replicas is omitted from here.
After studying this unit you
should be able to:
- describe some key events
in the evolution of life during the Palaeozoic Era, such as the first
appearance of major groups of invertebrates and vertebrates, and the
invasion of the land;
- identify some
common types of fossil organisms that were living in Palaeozoic seas,
and comment on their likely environment and geological age;
- make inferences from fossils about the biology and
mode of life of some Palaeozoic organisms.
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Introduction
 Introduction
Resource- The Palaeozoic Era was a very
important time in the history of life. Using evidence from fossils, we
start by looking at the Cambrian explosion, when many forms of animal
life first appeared about 545...
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1 The Cambrian explosion
- 1.1 A burst of evolution Resource
- One of the most important events
in the history of life began about 545 million years (Ma) ago, i.e. some
four billion years after the origin of the Earth, and over 3.3 billion
years after the origin of...
- 1.2 The Burgess Shale Resource
- High in the Canadian Rockies is
exposed a deposit of middle Cambrian age, about 530 Ma old, called the
Burgess Shale. It contains the fossils of animals that lived on a muddy
sea floor, and which were...
- 1.3 An overview of animal phyla Resource
- We have already met quite a few
different animal phyla, and it's useful to get an overview of all the
ones commonly found in the fossil record and their mode of life before
studying some in more detail....
- 1.4 The origin of the vertebrates Resource
- Vertebrates such as ourselves are
by definition animals with a backbone (or vertebral column, paired
limbs, a skull and various other structures. Until recently vertebrates
were thought to extend back...
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2 The Ordovician seas
- 2 The Ordovician seas Resource
- Collecting seashells on an
Ordovician beach would have been a rather curious experience. Whilst
most shells were made of similar materials to those found on a modern
beach, the detailed form of many would...
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3 The Silurian Period and the invasion of the
land
- 3 The Silurian Period and the
invasion of the land Resource
- What global event had reduced
global sea level at the end of Ordovician times, drastically affecting
shallow marine organisms, and leaving the diversity of early Silurian
life severely curtailed?
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4 Life in the Silurian sea
- 4.1 Trilobites Resource
- As we've seen, the Cambrian
explosion left the seas teeming with a huge variety of animals. In the
following activity you will study some of the marine life at one
particular time in the Palaeozoic Era...
- 4.2 Crinoids
Resource
- Figure 7 shows the fossilised
remains of a type of echinoderm called a crinoid (‘cry-noyed’). Although
crinoids occur today, they were far more common in the Palaeozoic and
Mesozoic Eras. Most crinoids...
- 4.3 Corals
Resource
- Corals are especially abundant in
the Wenlock Limestone.
- 4.4 Other Wenlock Limestone fossils Resource
- Among the other fossils common in
the Wenlock Limestone are brachiopods (Figure 12a and b), gastropods
(Figure 12c) and bryozoans (Figure 12d). You may need to reread Section
1.3 to remind yourself about...
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5 The Devonian Period
- 5 The Devonian Period Resource
- Environmental change is known to
have a significant impact on the evolution of life. For example,
widening oceans generate barriers between populations and promote
increasing genetic divergence between...
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6 Vertebrates move onto land
- 6.1 A difficult evolutionary
transition Resource
- As we saw in Section 3, the move
out of water on to land was a particularly difficult evolutionary
transition, requiring many adaptations.
- 6.2 An outline of vertebrate
evolution Resource
- Let's now place the early
evolution of tetrapods in perspective by taking an overview of the whole
of vertebrate evolution.
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References and Acknowledgements
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