Evidence of Evolution- Whales

Evidence of Evolution- Whales

​We are going to see a combination of evidences used to help see the the evolution of whales.

Cetaceans

Cetaceans (sih-TAY-shuns) are a group of animals made up of about 90 different species, including porpoises, dolphins, and whales. Like fish, Cetaceans spend their whole lives in the water. But, like mammals, they need to come to the surface to breathe air.

For a long time, scientists didn't know to classify cetaceans as mammals or as fish. But upon further investigation, even though they look very similar to fish, they share much more in common with mammals.

Multiple Choice

Which of the following would be a type of cetacean?

• A Shark

• A Dolphin

• A Dog

• A Goldfish

Multiple Choice

Which of the following diagrams best shows the relationship between cetaceans, fish, and mammals?

Did you know??

A lot of animal classification is determined by the dentition, or tooth structure of the animal! Take a look at the two teeth structures to the right. Mammals tend to have two roots on their teeth, whereas reptiles tend to have one root.

Examine the unknown tooth in comparison to the mammalian and the reptilian tooth. Do you think the animal this tooth came from was a mammal or a reptile?

Multiple Choice

Examine the unknown tooth in comparison to the mammalian and the reptilian tooth. Do you think the animal this tooth came from was a mammal or a reptile?

• It looks like this tooth came from a mammal

• It looks like this tooth came from a reptile.

Using Fossil Evidence

This is the fossil of an animal called Zeuglodon. It was previously thought to be a dinosaur, but in 1839, it was actually discovered to be an ancient whale! The root of the Zeuglodon teeth had two roots, like most land mammals. Reptiles, including dinosaurs, have teeth with one root. The Zeuglodon fossil looked different from any living whale, showing that whale species have changed over time.

Here is a close up of Zeuglodon!

Multiple Choice

What evidence about the Zeuglodon led scientists to conclusion it was an ancient whale and not an ancient dinosaur?

• The number of vertebrate

• It had two roots on the teeth

• It had a tiny pelvis and femur

• It had fur instead of scales

Skeleton Comparisons

The orca spends its life entirely in the water. It can be found in all of the world’s oceans. It grows to be about 20 feet (6 meters) long, and it hunts fish, seals, and other animals for food. You can see that Zeuglodon shares a lot of characteristics with modern orca.

Multiple Choice

There are more fossils of ancient whales besides the Zeuglodon. They show the many changes whales have undergone. These fossils that shows changes from one way of life to another are called:

• homologous structures

• vestigial structures

• transitional fossils

• strata

Let's take a look at some of the Transitional Fossils that show the changes that happened to ancient whales as they evolved into modern whales.

It's so cool.

Dorudon With flippers and tiny hindlimbs, Durodon wouldn’t have been able to move on land. Its fossils, which are an estimated 36–40 million years old, have been found in coastal areas around the world.

Rodhocetus probably spent time both in the water and on land. It probably moved speedily through water but quite awkwardly on land. Its fossils, which are about 46-47 million years old, have been found in modern-day Pakistan.

Ambulocetus means “walking whale.” Ambulocetus probably moved comfortably both in the water and on land. Its fossils,

which are about 49 million years old, have been found in modern-day Pakistan.

Pakicetus probably moved swiftly on land and spent most of its time there. However, molecular test results suggest that it ate mainly fish and other animals that lived in the water. Its fossils, which are about 50 million years old, have been found in modern-day Pakistan.

Open Ended

Summarize how the fossil cetacean ancestors changed over time.

Embryology

This is a dolphin embryo. It shows you how dolphins develop in utero over time. Pay attention to how their nostrils and how their hindlimbs change while developing.

Pay attention to how their nostrils and how their hindlimbs change in dolphin embryos while developing.

Multiple Choice

True or False: The nostrils of cetaceans start developing at the front of their faces, and then migrate to the top of their skulls. This is very similar to how nostril placement changed in ancient whale fossils to modern whales.

• True

• False

Molecular Biology Evidence

Whales make milk to feed their babies. Caseins are nutritional proteins that are found in milk. In the mid-1990s, one group of researchers decided to investigate which mammals are most closely related to whales by looking at the amino acids (monomers) sequences of casein proteins (polymer).

Multiple Choice

Which of the following statements helps summarize the reasoning of how the study of molecular biology helps establish evolutionary relationships:

• The more similar the molecules are, the most closely related the organisms are

• The more different the molecules are, the more closely related the organisms are

Casein Sequences

On the next slide, you will see the amino acid sequences of various mammals compared to whales. Based on the similarities and differences of the amino acid comparisons, determine which mammal is most closely related to whales and which is least closely related to whales.

Based on the similarities and differences of the amino acid comparisons, determine which mammal is most closely related to whales and which is least closely related to whales.

Multiple Choice

Which animal is most closely related to whales?

• Pig

• Cow

• Hippopotamus

• Camel

• Goat

Multiple Choice

Which animal is least closely related to whales?

• Hippopotamus

• Camel

• Goat

• Water buffalo

• Mouse