Lesson Plan 4

Evolutionary Trees

Learning Intention:

Understand evolutionary trees and how they show change over time.

Recognise that fossils provide information about organisms that inhabited the Earth millions of years ago.

 

Teachers Notes:

Fossils

–          Fossils are the preserved remains of plants or animals, over 10,000 years old. Body fossils are the preserved remains of a plant or animal’s body. Trace fossils are the remains of the activity of an animal, such as preserved track ways, footprints, fossilized egg shells, and nests.

–          Fossils provide evidence that organisms change over time as they provide a record of how species changed over time.

–          Fossils provide evidence of extinct species which could not adapt to their environment.

–          Fossils provide evidence of the similarities and differences between extinct and living species.

 

Evolutionary Trees

–          Evolutionary trees show that the appearance of new characteristics has caused divergence of species.

–          They create a timeline for the divergence of species and show which species are more closely related.

–          “v” shapes indicate related species with a common ancestor at the bottom of the “v”.

–          Trees can be drawn based on one character, for example the pentadactyl limb..

 

Common Ancestor

–          Humans share many characteristics with close relatives and a few with more distant-related species such as worms.

–          Shared characteristics and fossil records provide evidence for common ancestors.

–          The common ancestor of all species is thought to have been a single cell organism.

–          Evolution however does not specify where this common ancestor came from.

 

Pentadactyl limb

The pentadactyl limb has 5 digits on the hand and foot. It also has a specific pattern of bones. This structure consists of the humerus, the radius and the ulna, metacarpals and then the 5-digit fingers and toes. The pentadactyl limb is common to humans, other mammals (although whales and dolphins have lost their hind limbs), birds, dinosaurs, and other reptiles and amphibians. The pentadactyl limb is common to most tetrapods (4-limbed creatures). It is evidence of humans’ common ancestry with amphibians, reptiles and other mammals.Every pentadactyl limb has the same base structure of five digits but they all look very different and also do very different things. This is all because of evolution.

 

Starter (15 minutes)

Aim: to understand that change over long periods of time can lead to the formation of new animals due to natural selection and that this can be shown using an evolutionary tree.

Start the lesson by asking the class is they are familiar with the concept of a family tree. You can show a picture of one to help explain if there are any child that is not familiar. Explain how, in the same way we display the relationship between family members, we can display the relationship between different species using an evolutionary tree (define evolutionary tree). Explain that an evolutionary tree shows the relatedness of animals over time and can provide us with information about the past, similar to a family tree.

Next give each child a copy of the Evolutionary Tree Worksheet. Explain that you are going to create an evolutionary tree for the animals across the top of the worksheet. Explain that the animals are: two domestic cats (Persian and Siamese), a panther, a lion and a dog. Ask the children which animal they think the Siamese domestic cat is most related to. Prompt the children to match this with the Persian domestic cat as they are both small domestic cats, you may also point out the position of ears, and other facial characteristics which are more similar among the cats, than between the cat and panther. Join them together using a “v” shape (get the children to do this with you). Explain that the “v” shows that they are related. Next ask the children who they think the panther is most related to? Again prompt them to match the panther with the lion due to the larger size, behaviour, etc. Then draw a “v” between the lion and the panther. Next ask the class who they think the panther and lion are most closely related to, the domestic cats or the dog? They should notice that the cats will be more closely related as they have more characteristics in common than with the dog. Join the domestic cats and big cats with a bigger “v”. Explain how they are all related but less related than the domestic cats are to each other. Then finally add on the dog in an extended “v” shape.

Congratulate the class on completing their first evolutionary tree. Outline how it shows time, with the most recent animals (that we can still see today) at the top of the tree; and the older animals which are now extinct at the bottom. Get the children to draw an arrow onto their evolutionary tree to show the direction of time. Then, introduce the idea of common ancestor; stating that the common ancestor is the last ancestor of a group of animals we see today which shares common characteristics with all the animals within the group. Explain how there are lots of different common ancestors on an evolutionary tree. It is important to reiterate to the children how an evolutionary tree shows change over time on a large time scale of millions of years and it shows the divergence of different animals and helps us understand the changes that have occurred since the first animals walked the earth.

(Note: TheEvolutionary tree Resource Sheet shows a picture of the correct evolutionary tree with a time arrow and common ancestors marked on, to help you when teaching).

Main Body (30 minutes)

Aim: to reiterate the fact that change over long periods of time can lead to the formation of new animals due to natural selection and that this can be shown using an evolutionary tree. To understand that an evolutionary tree can be drawn based on a certain characteristic such as the pentadactyl limb.

Show the class images of a reptile (lizard), a bird, a human and a bat on a PowerPoint slide. Discuss with the class how different the four animals are. Then ask if they can see any similarities, do they have anything in common? Yes, they all have bones. They also all have a back bone – that is why all these animals are known as vertebrates. Prompt them to talk about bones. Do they think the bone structures in these animals are similar or different? Explain how you are now going to look at the bones in each animals arm so that you can answer this question.

Give each child the drawings of four bones in the arms/ limbs of each of these species (see bones worksheet – cut them up into four separate sheets). Discuss with the class how the images show the forearm limb from the four different animals – the human, the reptile, the bird and the bat. This limb is named the pentadactyl limb(at this point define pentadactyl limb). It is important that the children realise you are only looking at bone structure. First get them to determine which limb matches which animal.

Once they have decided which bone pictures belong to which animal, ask the children to colour in the bones that look similar with the same colour (i.e. colour all the humorous bones pink). The children should do this for all the bones in the forelimbs. As they do this walk around the class and make sure they are colouring in the correct bones. Especially make sure that the children notice that on the bird the longer bones at the end are fingers not a copy of the ulna and radius or extended wrist bones (as shown below). As they are colouring prompt the children to look for similarities between the bone size and shapes and encourage them to start thinking about which animals are more related than others.

bones image for plan

 

 

Once the children have coloured in all the bones talk through this as a class to check everyone has got it right (the correct colouring can be seen above).

Now explain how this time, rather than looking at the animals directly, you are going to build an evolutionary tree based on the specific characteristic of the pentadactyl limb. Start by asking the children which bone structure is most closely related to the humans bone structure. You will probably need to prompt them to look at the shape of the bones (whether they are long and narrow as in the bat and the human or fat and shorter as in the bird and reptile) and the gap in between the ulna and radius which is smaller in the human and the bat in comparison to the bird and the reptile. Once they have determined it is the bat then draw a “v” shape between the bat and the human. Next ask them whether they think the reptile is more closely related to the bird or the human again prompting them to look at the same properties. Once they have determined it is more closely related to the bird then draw another “v”. Remind them that the “v” shows the animals are related. Next join the two v’s together emphasising how they are all related due to the presence of the pentadactyl limb. Congratulate the class on completing their second evolutionary tree.

Note: the fingers are the latest thing to evolve, they have probably evolved since the final divergence of each animal. Therefore when looking at how the four animals are related you need to focus on the bones in the arm (there is a copy of the correct tree in the evolutionary tree resource sheet).

Also be careful as some characteristics can look the same but not be derived from a common ancestor. For example the wings of a bird and a bat have the same function and might be considered similar. However, a look at the bone structure reveals their distinct evolutionary paths. This indicates that they do not come from a common ancestor who had wings, but that both evolved wings for flight independently.

 

As before ask the children to draw a time arrow onto their evolutionary tree to show the direction of time and which animals are most recent and which are most distant. Also reiterate the idea of the common ancestor reminding the class that the common ancestor is the last ancestor of a group of animals which shares common characteristics with all the animals within the group. Ask them to draw circles where the common ancestors are found on the tree.

Now, as a class discuss what the common ancestor between the bird and the lizard may look like, what characteristics may it have? Ask the children if they think there is any way we can know what this animal looked like… they may say fossils. If they do then ask them what they know about fossils encouraging them to lead the discussion. If not then start the discussion yourself. Regardless of their answer, make sure you include the following points in your discussion:

– Fossils are the remains of ancient animals and plants, the traces or impressions of living things from past ages, or the traces of their activities.

– Fossils can be bones, whole animals (such as insects in amber or frozen mammals) or footprints. Fossils have been found on every continent on Earth.

– Fossils found deeper in the ground are older. Explain how fossils are found in the ground by palaeontologists. That fossils provide evidence for animals that are not here today and help us determine what those animals may have looked like. You may want to use this link to show how fossils are formed: http://www.nhm.ac.uk/nature-online/earth/fossils/fossil-folklore/how_are_fossils.htm .

Show an image of a feathered dinosaur or an archaeopteryx. If you can, try and get hold of a real fossil or replica fossil of the feathered dinosaur. Ask the children where in the tree they just build this organism should go? Prompt the children by asking them what characteristics it has, does it have feathers? What about the feet, claws and its facial shape? What creatures does it remind you off? Hopefully they will tell you that it looks like a bird (feathers, wings) and a reptile (face and feet/claws). Therefore you can discuss how it is the common ancestor of the birds and the reptiles. Ask them to draw an arrow and label to show where this common ancestor is on their evolutionary tree (shown on evolutionary tree resource sheet). If you have time discuss why it may not have survived leading to the evolution of the reptile and bird. For example it looks too heavy to fly easily and also too big to run/scurry around the forest ground so therefore it was more advantageous to evolve to be a specialist at one or the other rather than both.

Plenary (10 minutes)

Aim: to reinforce the understanding of fossils and how they are the remains/traces or impressions of living things.

Cut out the cards on the snap cards worksheet. In pairs the children should turn all the cards face down and then take it in turns to turn over two cards. If the fossil and the image of the animal matches then the child wins those cards otherwise they are turned back and it is their partners turn. If the children can state what the animal is they get a bonus point.

Homework

Explain to the children that they have found a fossil of the feathered dinosaur and they need to write a newspaper article explaining: what a fossil is, where the fossil was found, what characteristics it has and what they think it might be. They need to include a picture of the fossil either printed or hand drawn.

Lesson Assessment

1)    An evolutionary tree shows the change of animals over time. True or false

2)    You find a common ancestor at the bottom of each “v” shape. True or false

3)    Evolutionary trees cannot be based on characteristics such as the pentadactyl limb. True or false

4)    Fossils tell us about animals that have become extinct. True or false

5)    Name an example of a fossil. What two animals is it the common ancestor for?

 

Answers: 1) True 2) True 3) False 4) True 5) Feathered Dinosaur – birds and reptiles

 

Extra Material:

–          This is a really nice activity which describes how to make fossils for the children to see in the classroom: http://www.nps.gov/brca/forteachers/paleoact4.htm

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