Act. 99: A Whale of a Tale Challenge How are modern and fossil skeletons used to investigate evolution?

KeyVocabulary:Fossil RecordNatural Selection

Getting Started…Are whales mammals or fish?

How do you think whales evolved: do you think some mammals evolved from land to sea or that a type of fish evolved to have mammalian traits?

What type of evidence could help you answer this question?

Read the Introduction on page 48

Doing the Activity:1. Read “The Fossil Exhibit” on page 49

2. Follow the procedure on pages 49-50. Make sure you copy the data table into your

notebooks in step #1

Comparing Skeletons Similarities Differences

Group 1 Skeletons:

__A, M____________Group 2 Skeletons :

__B, D, O________Group 1 skeletons compared with Group 2 skeletons.

What can be inferred about the evolution of whales based on the physical characteristics?How can we decide which was the ancestor

of modern whales, Skeleton D or Skeleton B?

Evolution of whales has involved the extinction of some groups

and the formation of

others by branching - speciation

The evolution of aquatic traits in

this lineage of

mammals took about 20 million

years

How are whales and cows related then??

Whales and cows share a common ancestor

known as paraxonions. It is similar to a cousin

relationship!

Is there a trend in this evolutionary tree toward evolving to live in water?

Not only whales evolved from the

common ancestors on this evolutionary tree, but also cows, sheep,

pigs, and hippopotamuses

Analysis #1aSkeletal changes in the evolution of whales”

External hind limbs are lost and the bones either greatly reduced or lost entirely;

The skull changes size and shapeForelimbs turn into finsTail elongates due to loss of the pelvis and

external hind limbsThe tail vertebrae become thicker and largerThe enlarged neck vertebrae shrink (indicating

reduced need)

Analysis #1bInferences about changes in habitat because of skeletal changes:

These skeletal changes indicate a transition from predominantly land-dwelling animals to ones that lived partly in shallow water, and eventually to animals with an exclusively aquatic habitat.

Analysis #3Comparing skeletons can show similarities

and differences among species.

The numbers of these similarities and differences allow scientists to infer relationships among different animals/groups of organisms

If you have enough fossils, an evolutionary tree can be made.

Analysis #5Student answers will vary with their opinions

GREAT TRANSFORMATIONS

HomeworkAnalysis Question # 2Use Natural Selection to describe how/why ONE of these changes occurred.

Changes: Teeth, Rib Cage, Length, Limbs, Vertebrate, Skull shape/size etc.