Sort and compare: Trilobite evolution evidence

In this activity, your class will use images of trilobite fossils to explore how fossils preserve information about ancient life.

They will sort the fossils into orders (closely related groups) by observing characteristics and comparing them to see how trilobites changed over time.

This is a good activity to start exploring the topic of evolution with your class.

  • Key Stage: KS2 Year 6 (ages 10-11)
  • Time required: 20 minutes
  • Resource type: sorting activity, image bank
  • Theme: Evolution and inheritance (National Curriculum Year 6)

Learning outcomes

  • Learners will understand that fossils preserve information about living things which lived millions of years ago.
  • Learners will understand that living things have changed over time based on fossil evidence.

Running the activity

1. Download the PowerPoint presentation (PPT 5.9 MB) above. Using the first slide, introduce trilobites and establish what orders are (a group of more closely related animals).

2. Learners then make observations in order to sort nine trilobite images into three groups, based on the shapes of their bodies. You could run this activity:

a) in groups, if you print out and cut out the nine trilobite image (slides six, seven and eight) for each group
b) as a whole class on the screen

  • Are there any similarities in the overall shape of the trilobites?
  • Are there similarities in detailed features like eyes or spines?

Use the descriptions of the characteristics of each order (slide five) to help:

Redlichiida – These early trilobites tend to be very flat and have crescent shaped eyes. The third segment from the head often has large spines extending out to the side.

Phacopida – The name of this order means ‘lens face’, after their large compound eyes (eyes with many lenses). The lenses are visible as small bumps and packed together in a raised c-shape.

Asaphida – Trilobites in this order can have head and tail regions of similar size. Their heads are often smoother than other groups of trilobites.

3. Once the fossils have been grouped, learners choose one order and identify the similarities and differences between the fossils.

  • What are some similarities in shape or details of body parts?

4. Take one order of trilobites and arrange according to their age.

  • Have any characteristics changed over time?

Learners can reinforce their knowledge that fossils preserve information about the ways living things have changed by summarising the similarities shared by an order of trilobites, and describing how a characteristic has changed over time.

  • Printer and paper if you wish to print out the trilobite images.

Background science

Trilobites once were extremely common marine creatures, with palaeontologists recognizing nearly 4,000 genera of trilobites, grouped into around 10 orders.

Trilobites lived in all the Earth’s oceans for hundreds of millions of years. They also had tough exoskeletons which made them more likely to fossilise. This has preserved a detailed record of trilobite diversity. In many cases, enough fossils have been found to track changes in a type of trilobite over millions of years.

The detailed fossil record of trilobites shows how species gradually evolved, slowly changing form as they adapted to changing environments. In some cases, trilobites changed form only to slowly go back to the earlier shape. These cases illustrate how variation is a random process. Some variations in form become disadvantages to survival or reproduction. Over time pressure from natural selection pushes these populations back towards the earlier form.

Trilobites can be found in the fossil records from 521mya (million years ago) to 252mya. Despite their success over such a long time, the fossil record indicates that their numbers and diversity steadily declined for more than 100 million years.

Palaeontologists are still working out what led to this decline, but it is likely a combination of increasing predator diversity and environmental change, and trilobites were affected by several mass extinction events. A more recent study suggests that trilobites’ moulting habits may have also contributed to their eventual extinction.

While they did not evolve from trilobites, the closest living relatives today are horseshoe crabs.   

Suggested extension activities and differentiation

Get comfortable with trilobites
Somelearners might benefit from using the labelled line drawing as a guide to label the body parts of a trilobite fossil, before sorting all the images.

Simplify
Some learners might benefit from beginning with examining the fossils from just one order of trilobites and circling similarities. They can examine an image from one of the other orders and identify differences in key characteristics. Use the labelled trilobite diagram to help students describe differences.

Understanding relationships
To help learners understand the relationship between the trilobite fossils it may be useful to revisit how scientists group living things. All living things are grouped into three domains . Each domain of life is then divided into kingdoms, phyla, classes, orders, families, genera, then species. Trilobites are a class within the arthropod phylum.

Changing characteristics and adaptation
Trilobites have been extinct for millions of years. This means no one has been able to observe the behaviour of a live trilobite and there are many details scientists don’t know for certain. Fossil evidence gives scientists information they can use to come up with theories.

Learners can theorize how changes in a characteristic might have helped trilobites to survive or reproduce. Thinking about similar characteristics in modern animals can help with ideas. Learners should explain their theory and the evidence behind it to others. Drawing illustrations of the trilobites in action can help them explain their theory to other students.

Index fossils
Some fossils are so common that scientists can use them to figure out the age of other fossils or archaeological remains found in the same rock layer. Investigate how scientists use gradual changes in common types of fossil to work out the ages of rocks and fossils.

KS2 National Curriculum, Year 6 programme of study

Working scientifically

  • Identifying scientific evidence that has been used to support or refute ideas or arguments.
  • Use relevant scientific language and illustrations to discuss, communicate and justify their scientific ideas.

Evolution and inheritance

  • Recognise that living things have changed over time and that fossils provide information about living things that inhabited the Earth millions of years ago.
  • Building on what they learned about in year 3, pupils find out more about how living things on earth have changed over time.

Related activities and resources

External Sites