Evidence-of-Evolution Worksheet.pdf - Evidence of Evolution ... - Free Printable

Let’s go step by step to answer each question on the worksheet.

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Question 1: Which animal is most closely related to whales?

Look at the “Fossils” table. It shows how limb bones changed over time in different animals — from Pakicetus (oldest) to modern Whale.

Now look at the “Living Animals” row below the fossils. You’ll see that Hippos have leg bones that are very similar in shape and structure to the early whale ancestors like Ambulocetus or Rodhocetus. Also, scientists know from DNA and fossil evidence that hippos are the closest living relatives to whales.

✔ So, the answer is: Hippos

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Question 2: Explain why scientists believe that land-dwelling mammals might be the ancestors of whales.

Look again at the fossil sequence:

- Pakicetus → had legs and walked on land
- Ambulocetus → could walk AND swim
- Rodhocetus → mostly swam, but still had small hind legs
- Basilosaurus → almost fully aquatic, tiny back legs
- Modern Whale → no visible back legs, lives only in water

This shows a clear change over time: from land-walking → swimming → fully ocean-living.

Also, even today, some whales have tiny leftover hip bones inside their bodies — which don’t help them swim, but show they came from animals that once walked on land.

✔ So, scientists think whales evolved from land mammals because:
- Fossils show gradual changes from land to sea.
- Whales still have hidden leg bones from their land ancestors.

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Question 3: Make up the biggest change you can think of between the earliest known land-dwelling mammal ancestor and the modern whale.

The earliest ancestor shown is Pakicetus — it looked kind of like a dog or wolf, with four legs, lived near water, ate meat.

Modern whales are huge, live entirely in water, breathe through blowholes, have flippers instead of arms, and no back legs.

So one BIG change:
→ From walking on four legs on land → to having no back legs and using tail flukes to swim in the ocean.

Another big change:
→ From breathing air through nose/mouth on land → to breathing through a blowhole on top of head while floating in water.

✔ Pick one major change — for example:
They went from walking on land with four legs to swimming in the ocean with no back legs and a powerful tail.

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Question 4: What is the biggest change that happened after the first whales appeared in the environment?

After the first whales (like Pakicetus or Ambulocetus), the next ones (Rodhocetus, Basilosaurus) started spending more time in water.

Biggest change AFTER first whales appeared:
→ They lost their back legs completely (or reduced them to tiny useless bones).
→ Their front legs turned into flippers.
→ Their tails became flat and horizontal for swimming.
→ Their nostrils moved to the top of the head (became blowholes).

✔ One clear answer:
Their body shape changed so they could swim better — legs became flippers, tail became a flipper, and nostrils moved to the top of the head.

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Final Answer:

1. Hippos
2. Scientists believe land-dwelling mammals are ancestors of whales because fossils show a gradual change from land-walking to ocean-swimming, and modern whales still have tiny leftover leg bones.
3. The biggest change is going from walking on four legs on land to swimming in the ocean with no back legs and a strong tail.
4. After the first whales appeared, their bodies changed to become better swimmers — legs turned into flippers, tail became a flipper, and nostrils moved to the top of the head.