Sponge: Set up Cornell Notes on pg. 51

Topic: 5.4 Evolution: Evidence for Evolution: Fossil Record

Essential Question: Explain why the fossil record is one of the key pieces of evidence for the theory of evolution.

BIOZONE: 238-251 due 11/05

5.4 Evolution: Evidence for Evolution

Key Vocabulary:Fossil RecordHomologous StructuresEmbryology

Explain why the fossil record is one of the key pieces of evidence for the theory of evolution.

BIOZONE: 238-251 due 11/05

Pg. 50 Fossil Record

Homologous Structures

Embryology

On Your own: Draw your own picture of each

Evidence for Evolution (2m4s)

Assessment Statement

• 5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures

Evidence for EvolutionMajor pieces of evidence for evolution

• Artificial Selection• Fossil Record• Homologous Anatomical Structures• Embryology

Fossil Record• The fossil record gives scientists clues about what life was like millions of

years ago• Paleontologists collect and classify fossils in an organized fashion• The fossil record has provided convincing evidence for Earth’s evolutionary

past

FEMURPELVIS

Analyze this picture of a baleen whale. Using the idea of evolution by means of natural selection, tell me why this whale has a pelvis and a femur.

PELVIS

FEMUR

Baleen Whale(Present day)

Dorudon(40 m.y.a.)

Baleen Whale(Present day)

Ambulocetus(50 m.y.a.)

Dorudon(40 m.y.a.)

Baleen Whale(Present day)

Pakicetus(52 m.y.a.)

Ambulocetus(50 m.y.a.)

Dorudon(40 m.y.a.)

Baleen Whale(Present day)

Diacodexis(55 m.y.a.)

Pakicetus(52 m.y.a.)

Ambulocetus(50 m.y.a.)

Dorudon(40 m.y.a.)

Baleen Whale(Present day)

• Hippos are the closest living relatives of whales, but they are not the ancestors of whales

• Rhinos are not “ancestors” of pigs

• They share a common ancestor somewhere back in time

• This shows that cows/sheep are closer relatives to pigs than to rhinos or modern whales

Fossil Record• Overall, life which existed more than 500 million years ago was very different

from life today• Although Earth has had extensive oceans for most of its existence, fish fossils

have only been found in rocks 500 million years old or younger• less than 15% of the history of life

Fossil Record• Although most of the top predators today are

mammals such as bear, orcas, big cats, wolves, etc; none of them existed at the time of the dinosaurs or before

• Apart from organisms such as certain types of sharks, cockroaches or ferns, many living organisms today have no identical form in the fossil record

• The modern great white shark has been around from between 11-16 million years!

• Humans (homo sapiens) 50,000-100,000 years ago

• Cockroaches have roamed the planet for as long as 350,000,000 years with little change

Megalodon partial fossil

Great White Skeleton

*sizes not to scale

Fossil Record• One conclusion that can be drawn from

observing fossils is that life on Earth is CONSTANTLY changing

• Most of the changes have been over huge timescales

• Hundreds of thousands – millions of years

• The fossil record is FAR from complete

Homologous Anatomical Structures• Homologous anatomical structures: which are structures that are similar in

form and function but which are found in seemingly dissimilar species

Homologous Anatomical Structures• One of the most striking examples:

• Five-fingered limb found in animals such as humans, whales, and bats• Called pentadactyl limbs

• Penta= five• Dactyl= fingers

Homologous Anatomical Structures• When we compare a whale’s front fin to the forearm of a human or to a bat’s

wing we find the following bones• Humerus• Radius• Ulna • Carpals

Homologous Anatomical Structures• Although the shape and number of bones may vary, the general format is the

same, DEPITE THE FACT THAT THE FUNCTIONS OF THE LIMBS MAY BE VERY DIFFERENT

What are the different functions of the limbs from different animals?

Homologous Anatomical Structures• Darwin explained that homologous structures were not just a coincidence

but they are evidence that the organisms in question have a COMMON ANCESTOR

Homologous Anatomical Structures• They are of differing sizes and in morphology• BUT, the basic shape and position of the limb bones are the same• THIS WOULD SUGGEST THAT ALL FIVE-FINGERED ORGANISMS HAVE A

COMMON ANCESTOR

Common Ancestors: Mammalia

Common Ancestors: Mammalia

Humans and chimpanzees

Common Ancestors: Mammalia

Humans and Squirrels

Common Ancestors: Mammalia

Humans and Elephants

Common Ancestors: Mammalia

Humans and Duck-billed platypus

EmbryologyEmbryology: The study of embryos• The similar features of embryos in very different organisms suggests

evolution from a distant common ancestor

e

Anatomy of an embryo

Larva

Adult barnacleAdult crab

– identical larvae, but different adult body forms– similar embryos, but look and behave very differently

Darwin studied the embryos of crabs and barnacles:Embryology

Look for the similarities of the embryosEmbryology

Embryology