whales: walking into activity the past - national...

Virus and the Whale: Exploring Evolution in Creatures Small and Large

7

Activ

ity

165

Whales with knees and toes? Incredible as it seems, whales once walked on legs and lived on land. Millions of years of biological change have erased the whale’s legs from its body. But a faint trace remains. Hidden inside the streamlined body of many modern whales are tiny hip and leg bones. The story of how the whale—marvel of the oceans—evolved from a four-legged mammal is an amazing one. So far, it provides one of the best examples of how organisms change over time. And like whales, the story is still evolving. Just about everything to do with whales was once a big puzzle, even what kind of animal it was. Fish or mammal? Scientists had trouble deciding. From the small dolphin to the enormous grey whale, these animals look and live like fish. They can’t survive out of water—but on the other hand, they can drown in water. Every 15 minutes or so they have to swim to the water’s surface to breathe. Like all mammals, whales are warm-blooded, give birth to babies rather than lay eggs, and nurse their young with milk. They even have a belly button.

WHALES:

Walking Into the Past

Philip Gingerich, paleontologist at the University of Michigan, digs for fossil whales.Photo courtesy University of Michigan Museum of Paleontology.

Copyright © 2006 NSTA. All rights reserved. For more information, go to www.nsta.org/permissions.

Whales: Walking Into the Past

7Ac

tivity

166

So, if whales are mammals, how did they come to live like fish? Could their an-cestors have been land mammals that gradually took to the oceans? When scientists first asked these questions, there was little fossil evidence to provide answers. Until, that is, paleontologist Philip Gingerich discovered a bone in the desert of Pakistan. Many of the great scientific discoveries happen by accident, if the scientist is open to surprises. Philip Gingerich wasn’t looking for whales when he arrived in Paki-stan in 1977 with a team of international scientists. Dr. Gingerich was an expert on extinct land mammals. So he was disappointed to find that the first place he had tar-geted to look for fossils was an ancient seashore. The rocks were filled with fossilized snails and other shellfish—not the best place to find the bones of a land mammal. Like kids in a giant sandbox, Gingerich and his team went to work anyway. After a week of scouring the exposed rocks, they found a few pieces of bone that looked promising: They could make out part of a pelvis and a backbone. Gingerich recalls joking with his team about finding a “walking whale” with hips and legs, but back then it was just a joke. The team assumed that the fossils were bits and pieces of an ancient elephant ancestor, a land mammal that had drifted out to sea after death. But on a December day in 1979, the team found a specimen that was not so easy to explain. Embedded in rock as hard as cement, it was a curious fossil skull. Ging-erich took the skull home to his lab. When the fossil was cleaned up, Gingerich could see that it was no bigger than a wolf ’s skull and had many wolf-like features. The teeth were a mix of canines and molars, and the nostrils were set close to the snout. But at-tached to the skull was a set of tiny thickened ear bones. The only animals on Earth, living or extinct, that have ear bones thickened this way are the whales. Gingerich named the creature Pakicetus (pack-eh-SEA-tus), Whale of Pakistan. It lived about 48.5 million years ago. Based on the land mammal-like features of the skull, Gingerich hypothesized that this whale probably went into the water to

Philip Gingerich searches for ancient whales in the deserts of Pakistan.SMM Lonnie Broden illustration.



7

Activ

ity

167

feed but came out on land to rest and to give birth. After the unexpected discovery of Pakicetus, Gingerich began to hunt for whales in earnest. Whale fossils are large, and they are relatively easy to find in the desert. Sometimes the wind lends a hand by scouring away the sands and shales, leaving entire skeletons exposed. One valley in Egypt was especially rich in whales. On a series of visits starting in 1983, Gingerich and his team found virtually a whale a day. The final tally came to 379 whales. He found some with hipbones, but Gingerich also hoped to find legs and feet. In 1989 Gingerich was mapping the spine of a well-preserved 50-foot-long skel-eton of Basilosaurus (bah-sill-oh-SOAR-us), a fossil whale that lived about 10 million years after Pakicetus. Two-thirds of the way down the spine he found a small round bone standing vertically. This seemed out of place, and the top was weathered away. When the rest was excavated, the bone proved to be an upper leg bone with the knee joint preserved. No one had ever seen the knee of a whale before. Counting down the spine, this bone was near the 48th vertebra. The whole team went to work brushing sand away from this part of all the Basilosaurus that had been mapped so far. Soon they found, astonishingly, not only more hips and upper legs, but also lower leg bones, anklebones, and finally, one by one, the bones of three tiny toes. These were the first hind limbs and feet ever found with a fossil whale skeleton. Basilosaurus was a huge ocean-going whale, with retracted nostrils forming a blowhole halfway up its four-foot-long skull. Its body was equipped with legs, but they were too small to support the animal’s weight on land. Gingerich predicted that scientists would unearth many more missing links be-tween land and sea whales. He wasn’t disappointed. Some of the most important finds were yet to come. In the 1990s J. G. M. Thewissen and Gingerich discovered two whales that were almost as old as Pakicetus. Both had legs larger than Basilosaurus, even though the skeletons were only 10 to 12 feet long. One was named Ambulocetus natans (am-bue-low-SEA-tus-NAY-tans) and the other Rodhocetus kasranii (row-deh-SEA-tus-kaz-RAN-nee-eye). Like Pakicetus, both of these whales found their food in water and were good swimmers, but both still hitched their way ashore to rest and to give birth. Some crucial parts of the Rodhocetus skeleton were still missing. The hands, feet, and tail were poorly known. But Gingerich persevered, and eventually his team found

Rodhocetus, “the barely walking whale.”John Klausmeyer illustration.



7Ac

tivity

168

a complementary Rodhocetus skeleton with hands and feet intact. He named this one Rodhocetus balochistanensis (bah-low-CHIS-stan-en-sis), after the province in Pakistan where it was found. This discovery brought new surprises. The middle three fingers of each hand retained a tiny hoof. And the anklebones proved to be the kind that belonged only to hoofed mammals known as artiodactyls (arty-oh-DAK-tils). Artiodactyls include cows, goats, pigs, and hippos. Rodhocetus combined features of an aquatic whale with features of a hoofed mammal all in the same skeleton. Scientists doing DNA studies had already claimed that the whale’s closest liv-ing relatives were artiodactyls like the hippopotamus, and here was confirmation. The fossil record and DNA evidence were now saying the same thing. Rodhocetus was like an arrow pointing backward to a hoofed ancestor and forward to an ocean-dwelling dolphin. In this activity you’ll have a chance to meet Rodhocetus, the barely walking whale, excavate and sort some “fossils” of your own, and learn how to read bones like a pa-leontologist to understand the whale’s remarkable transition from land to sea.



7

Activ

ity

169

PART ONESweet excavationDiscovering fossils is not like in the movies where whole skeletons of ancient critters magically reveal themselves in all their magnificence at the flick of a whiskbroom. The process is more like reassembling bits of roadkill that were buried millions of years ago and cemented into rock. Finding fossil bones is just the first step. The bones then have to be carefully dug up, and then packed and shipped back to the lab. There they are cleaned, studied, and assembled. It is slow work. Try your own hand at excavating some fossil “bones” and making sense of your finds. An exciting new discovery of “fossil pretzel bones” has arrived in your lab. Your job is to excavate, sort, and assemble the bones. Then see if you can assemble the parts well enough to identify what kind of pretzel creature these bones belong to.

Work with a partnerEach team will need: Pretzel Species sheet stiff paper or cardboard liquid glue

Either of two options:

1 Fossil Evidence Envelope pretzel broken into 3–4 pieces envelope

2 Cookie Fossil Rocks cookie dough baked with 3–4 pretzel pieces inside big nail or metal nail file

PREP NOTE: This activity can be done in either of the following two ways, depending on the amount of preparation time available:

Fossil Evidence Envelope: To prepare, break a pretzel into about 3–4 parts and place the parts into an en-velope. For more challenge, add extra pretzel parts, remove some, or try work-ing with several shapes of pretzels and mix the parts.

Cookie Fossil Rocks:To make each cookie fossil rock, mix pretzel pieces with enough cookie dough to contain them. Bake according to cookie directions. Hard, dry cookies will be difficult to excavate.



7Ac

tivity

170

1 Making Sense of Fossils a Look at the Pretzel Species sheet of some known species of the pretzel

family to get familiar with their body forms. Open your “fossil evidence envelope” or excavate your “cookie fossil rocks” with a tool like a metal nail file. Lay out the pretzel parts.

b You may or may not have parts for a whole animal, but what you do have represents ONE species. Some of the parts may have been eaten by scaven-gers or gotten lost. Assemble the parts in a way that makes sense, using the shapes on the Pretzel Species sheet to help you sort and assemble.

c When you have assembled the parts of the pretzel animal, glue them to a sheet of paper.

d If you don’t have a whole animal, draw in what you think are the missing parts.

2 Consider This Does your pretzel look like one of the known

species or is it a new variety? Describe how your fossil finds compare to the ones on the Pretzel Species sheet.

When scientists discover a new kind of animal, they have the honor of naming the new species. If you think your pretzel bones belong to a new and different pretzel species, make up a name, and write it here.



7

Activ

ity

171

Pretzel Species: These are some members of the Pretzel Family

Pretzel cubicus Pretzel normalist

Pretzel giganticusPretzel stickia

Lind

a Al

lison

illu

stra

tion.



7Ac

tivity

172

PART TWORead some bonesWhen Philip Gingerich found the mystery bones in Pakistan, he knew they were not the bones of a modern animal. Gingerich knew he was digging in a layer of rocks that was about 47 million years old, which gave him a good estimate of about how old the bones were. He also knew from studying the rocks that the bones had been de-posited near a shallow sea. He took the bones back to his lab and after many months of painstaking work, his team cleaned and assembled the skeleton of the animal he named Rodhocetus. Even if a bone was buried for millions of years, a paleontologist can study a fossil bone and learn many things about the animal it came from. By comparing the shapes of fossil bones to modern bones, a lot can be learned about how the fossil animal might have lived and worked.

Work with a partner Each team will need: One Mystery Fossil Bones card (cut separate cards for Fore Limbs, Hind Limbs,

Skull & Teeth, OR Spine, Neck, & Ribs) One matching Some Known Bones sheet (Fore Limbs, Hind Limbs, Skull &

Teeth, OR Spine, Neck, & Ribs) One Sum It Up sheet (Fore Limbs & Hind Limbs OR Skull & Spine) Scissors

1 Bone Reading Study some pictures of mystery fossil bones excavated by Dr. Gingerich in Paki-

stan. See how much information you can “read” from these mystery fossil bones by comparing them to the bones of some modern animals alive today.

Every team should get a Mystery Fossil Bone card and the matching Some Known Bones sheet. Complete the questions in the challenge section of the Some Known Bones sheet.



7

Activ

ity

173

MYS

TERY

FO

SSIL

BO

NES

: SKU

LL &

TEE

TH

MYS

TERY

FO

SSIL

BO

NES

: HIN

D L

IMBS

MYS

TERY

FO

SSIL

BO

NES

: SPI

NE,

NEC

K, &

RIB

S

MYS

TERY

FO

SSIL

BO

NES

: FO

RE L

IMBS

Lind

a Al

lison

illu

stra

tion.



7Ac

tivity

174

DO

LPH

IN (S

WIM

MER

)

WO

LF (R

UN

NER

)

MO

NKE

Y (C

LIM

BER)

N

ostr

ils o

n to

p of

sku

ll

Eyes

pos

itio

ned

on t

he s

ides

CHA

LLE

NG

E:

FIN

D

THE

MO

DER

N

SKU

LL

AN

D T

EETH

MO

ST L

IKE

THE

MYS

TERY

FO

SSIL

BO

NES

.

1. Ge

t th

e ca

rd “

Mys

tery

Fos

sil

Bone

s: S

kull

and

Teet

h.”

2. C

ompa

re t

he m

yste

ry s

kull

and

teet

h to

the

bon

es o

f m

oder

n an

imal

s sh

own

on t

his

page

.

3. W

hich

sku

ll an

d te

eth

do y

ou

thin

k ar

e m

ost

like

the

Mys

tery

Fo

ssil

Bone

s?

____

____

____

____

____

____

4. L

ist

the

clue

s th

at h

elpe

d yo

u de

cide

:

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

5. B

ased

on

the

bone

clu

es, w

hat

type

of

crit

ter

did

the

Mys

tery

Fo

ssil

Bone

s be

long

to?

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

An a

nim

al‛s

skul

l ac

ts li

ke a

har

d ha

t to

prot

ect i

ts b

rain

. Sh

arp

teet

h ar

e su

ited

for t

earin

g in

to fl

esh;

fl at

teet

h ar

e be

tter

for

grin

ding

plan

t foo

ds.

Anim

als w

ith la

rge

eye

sock

ets p

oint

ing

ahea

d ha

ve g

ood

forw

ard

visio

n wh

ile

eyes

to th

e sid

es a

re b

ette

r for

seei

ng a

ll ar

ound

.

W

olve

s us

e th

eir

forw

ard-

poin

ting

eye

s an

d no

se

for

hunt

ing.

Sha

rp t

eeth

sta

b an

d ho

ld p

rey.

Mon

keys

use

thei

r kee

n ey

es a

nd n

ose

for fi

ndi

ng f

ood.

Th

ey u

se t

heir

div

erse

tee

th t

o ea

t a

mix

ed d

iet.

D

olph

ins

brea

the

at t

he w

ater

‛s su

rfac

e fr

om

nost

rils

on

top

of t

heir

hea

d.

Not

e ho

w th

e sh

apes

of

the

bone

s gi

ve c

lues

to

an

anim

al‛s

lifes

tyle

. Pegg

ed t

eeth

g

rip

fi sh

Larg

e ey

es

in f

ront

Nos

trils

fron

t

Poin

ted

teet

hFl

at t

eeth

Larg

eey

es in

fro

ntSk

ull r

idge

an

chor

s st

rong

jaw

mus

cles

Bone

-cr

acki

ng

mol

ars

Shar

p te

eth

tear

mea

t

Nos

trils

fron

t

SKU

LL &

TEE

TH:

Som

e Kn

own

Bone

s

Lind

a Al

lison

illu

stra

tion.



7

Activ

ity

175

FORE

LIM

BS: S

ome

Know

n Bo

nes

Sho

ulde

rjo

int

mov

esm

ainl

y fo

rwar

dan

d ba

ck

Com

pact

fe

et,

shor

t to

es

Long

leg

bone

s

Runs

on

tips

of

toes

DO

LPH

IN (S

WIM

MER

)

WO

LF (R

UN

NER

)

MO

NKE

Y (C

LIM

BER)

Ani

mal

s of

ten

use

thei

r fo

re li

mbs

or

fron

t le

gs f

or

spec

ializ

ed jo

bs li

ke d

iggi

ng, p

addl

ing,

and

gra

bbin

g,

Thei

r b

ack

legs

are

mai

nly

used

for

loco

mot

ion.

N

otic

e ho

w di

ffer

ent

anim

als

use

thei

r fo

re li

mbs

in

diff

eren

t wa

ys:

W

olve

s ru

n on

the

ir lo

ng le

gs a

nd c

ompa

ct f

eet.

St

rong

sho

ulde

rs s

uppo

rt t

heir

bod

y we

ight

.

M

onke

ys s

wing

thr

ough

tre

es w

ith

thei

r lo

ng

arm

s an

d gr

aspi

ng h

ands

.

Dol

phin

s sw

im u

sing

the

ir fl

ippe

rs a

s pa

ddle

s.

Not

e ho

w th

e sh

apes

of

the

bone

s gi

ve c

lues

to

an

anim

al‛s

lifes

tyle

.

CHA

LLE

NG

E:

FIN

D T

HE

MO

DER

N F

ORE

LI

MBS

MO

ST L

IKE

THE

MYS

TERY

FO

SSIL

BO

NES

.

1. Ge

t th

e ca

rd “M

yste

ry F

ossi

l Bo

nes:

For

e Li

mbs

.”

2. C

ompa

re t

he m

yste

ry f

ore

limbs

to

the

bone

s of

mod

ern

anim

als

show

n on

thi

s pa

ge.

3.

Whi

ch f

ore

limbs

do

you

thin

k ar

e m

ost

like

the

Mys

tery

Fos

sil

Bone

s?

____

____

____

____

____

____

_

4. L

ist

the

clue

s th

at h

elpe

d yo

u de

cide

:

____

____

____

____

____

____

_

____

____

____

____

____

____

_

____

____

____

____

____

____

_

____

____

____

____

____

____

_

5. B

ased

on

the

bone

clu

es, w

hat

type

of

crit

ter

did

the

Mys

tery

Fo

ssil

Bone

s be

long

to?

____

____

____

____

____

____

_

____

____

____

____

____

____

_

____

____

____

____

____

____

_

Lar

ge, s

tron

gsh

ould

ers

Shor

t, h

eavy

fo

re li

mbs

Flat

, sti

ff fl

ippe

rs

Stro

ng e

dge

of t

hefli

pper

cut

s in

to t

he w

ater

Larg

e sh

ould

ers

Opp

osab

le

thum

b Lo

ng

fore

lim

bs

Flex

ible

wri

st

Long

han

d an

d fin

gers

Lind

a Al

lison

illu

stra

tion.



7Ac

tivity

176

HIN

D L

IMBS

: Som

e Kn

own

Bone

s

CHA

LLE

NG

E:

FIN

D T

HE

MO

DER

N H

IND

LI

MBS

MO

ST L

IKE

THE

MYS

TERY

FO

SSIL

BO

NES

.

1. Ge

t th

e ca

rd “M

yste

ry F

ossi

l Bo

nes:

Hin

d Li

mbs

.”

2. C

ompa

re t

he m

yste

ry h

ind

limbs

to

the

bone

s of

mod

ern

anim

als

show

n on

thi

s pa

ge.

3.

Whi

ch h

ind

limbs

do

you

thin

k ar

e m

ost

like

the

Mys

tery

Fos

sil

Bone

s?

____

____

____

____

____

____

4. L

ist

the

clue

s th

at h

elpe

d yo

u de

cide

:

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

5. B

ased

on

the

bone

clu

es, w

hat

type

of

crit

ter

did

the

Mys

tery

Fo

ssil

Bone

s be

long

to?

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

DO

LPH

IN (S

WIM

MER

)

WO

LF (R

UN

NER

)

MO

NKE

Y (C

LIM

BER)

Ani

mal

s us

e th

eir

hind

lim

bs o

r le

gs m

ostl

y fo

r lo

-co

mot

ion.

The

ir f

ront

legs

are

oft

en u

sed

for

mor

e sp

ecia

lized

jobs

like

dig

ging

, pad

dlin

g, o

r gr

abbi

ng.

N

otic

e ho

w di

ffer

ent

anim

als

use

thei

r hi

nd li

mbs

:

Wol

ves

run

on t

heir

long

legs

and

com

pact

fee

t.

Stro

ng h

ips

supp

ort

thei

r bo

dy w

eigh

t.

M

onke

ys s

wing

thr

ough

tre

e br

anch

es w

ith

thei

r lo

ng le

gs a

nd g

rasp

ing

feet

.

D

olph

ins

swim

thr

ough

wat

er w

ith

thei

r

stre

amlin

ed b

odie

s. T

hey

lack

legs

.

Not

e ho

w th

e sh

apes

of

the

bone

s gi

ve c

lues

to

an

anim

al‛s

lifes

tyle

.

Stro

ng h

ip b

ones

Thum

bs

on f

eet

Long

flex

ible

to

es

Hip

join

t ha

sa

wide

ran

geof

mot

ion

Stro

ng,

weig

ht-

bear

ing

hips

Com

pact

feet

,sh

ort

toes

Hip

join

t m

oves

mai

nly

forw

ard

and

back

Long

leg

bone

s

Runs

on

tips

of

toes

Dol

phin

s ha

ve n

o hi

nd le

gs o

n th

e ou

tsid

e, b

ut

thei

r sk

elet

ons

have

tin

y, u

sele

ss le

g bo

nes

calle

d ve

stig

es.

v

esti

ge le

g bo

ne

Lind

a Al

lison

illu

stra

tion.



7

Activ

ity

177

An

anim

al‛s

spin

e ac

ts a

s a

rod

from

whi

ch t

he

othe

r bo

nes

are

hung

. It

is m

ade

of s

ecti

ons

calle

d ve

rteb

rae

that

for

m a

str

ong,

flex

ible

sup

port

and

pr

ovid

e an

chor

s fo

r th

e m

uscl

es. R

ibs

form

a c

age

to p

rote

ct h

eart

and

lung

s. N

otic

e ho

w di

ffer

ent

anim

als

use

the

spin

e in

dif

fere

nt w

ays:

W

olve

s us

e th

eir

long

nec

ks t

o m

ove

the

head

fo

r be

tter

sig

ht, s

mel

l, an

d he

arin

g.

Mon

keys

tra

vel t

hrou

gh t

rees

usi

ng t

heir

long

ta

ils f

or g

rabb

ing

and

bala

ncin

g. T

heir

flex

ible

ne

cks

aid

thei

r ke

en v

isio

n.

D

olph

ins

swim

usi

ng t

heir

pow

erfu

l tai

ls in

an

up

and

dow

n m

otio

n to

pus

h th

roug

h th

e wa

ter.

Not

e ho

w th

e sh

apes

of

the

bone

s gi

ve c

lues

to

an a

nim

al‛s

lifes

tyle

.

SPIN

E, N

ECK,

& R

IBS:

Som

e Kn

own

Bone

sCH

ALL

EN

GE

: FI

ND

TH

E M

OD

ERN

SPI

NE,

N

ECK

& RI

BS M

OST

LIK

E TH

E M

YSTE

RY F

OSS

IL B

ON

ES.

1. Ge

t th

e ca

rd “M

yste

ry F

ossi

l Bo

nes:

Spi

ne, N

eck,

& R

ibs.

”

2. C

ompa

re th

e m

yste

ry sp

ine,

ne

ck, &

ribs

to th

e bo

nes o

f m

oder

n an

imals

show

n on

this

page

.

3. W

hich

spi

ne, n

eck,

& r

ibs

do y

ou t

hink

are

mos

t lik

e th

e M

yste

ry F

ossi

l Bon

es?

____

____

____

____

____

____

4. L

ist

the

clue

s th

at h

elpe

d yo

u de

cide

:

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

5. B

ased

on

the

bone

clu

es, w

hat

type

of

crit

ter

did

the

Mys

tery

Fo

ssil

Bone

s be

long

to?

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

DO

LPH

IN (S

WIM

MER

)

WO

LF (R

UN

NER

)

Flex

ible

gr

aspi

ng tail

Long

flex

ible

nec

k

Long

ba

lanc

ing

tail

MO

NKE

Y (C

LIM

BER)

Str

eam

lined

bod

y sh

ape

Long

pow

erfu

l tai

l

Shor

t, s

tabl

e ne

ck

Long

flex

ible

nec

k

Dee

p na

rrow

che

st

Lind

a Al

lison

illu

stra

tion.



7Ac

tivity

178

2 Share Your Findings Scientists seldom find complete skeletons. To learn more, they often must share

information from other skeletons and from other dig sites.

a Partner with another group so Fore and Hind Limbs teams work together and Skull and Spine teams work together.

b Discuss your findings with partner group, and summarize them on one of the Sum It Up charts. See if you can come to an agreement about how your mystery animal moved, what it ate, and its habitat.

Sum It Up: Fore limbs and hind limbs

TEAMANALYSIS: Note your ideas about type of animal and its lifestyle

Fore Limbs

Hind Limbs

Both Teams Which of the three modern animals might have a body part similar to this?

Summarize:How mystery animal moved, what it ate, and its habitat



7

Activ

ity

179

Sum It Up: Skull and spine

TEAMANALYSIS: Note your ideas about type of animal and its lifestyle

Skull & Teeth

Spine, Neck, & Ribs

Both Teams Which of the three modern animals might have a body part similar to this?

Summarize:How mystery animal moved, what it ate, and its habitat

3 Consider This Philip Gingerich named the mystery bones Rodhocetus, the barely walking whale.

This whale was found in an ancient shallow water habitat. After analyzing the bones, Dr. Gingerich believes that this animal lived both in and out of the water, and it was a meat eater that breathed air. How does your team’s conclusion agree or disagree with Gingerich’s analysis?



7Ac

tivity

180

PART THREECreature featuresWhen a new fossil skeleton is discovered, one of the first questions a scientist asks is what animal or family of animals it is similar to. Even a partial skeleton allows a pa-leontologist to identify features that match with other animals. By identifying similar features, scientists can sort which animals are closer relatives and where an animal fits into the overall scheme of living things. In the case of extinct animals, scientists can attempt to sort out if they are the ancestors of living animals, and how they evolved over time. Take the next few minutes to consider the assembled Rodhocetus skeleton. Com-pare it to the skeleton of a modern dolphin (a type of small whale) and a modern shark. These two aquatic animals are similar in size but belong to different families. Check out the creature’s features. Then decide if Rodhocetus is more closely related to a shark than to a dolphin.

Work with a partnerEach team will need: Creature Features: Comparing Anatomy sheet

1 Comparing Skeletons Compare the three skeletons on the Creature Features sheet.

Would you say the modern whale or the modern shark is a closer relative of Rodhocetus? List the clues you noticed that helped you decide.



7

Activ

ity

181

RODH

OCE

TUS

SHA

RK

DO

LPH

IN

Lind

a Al

lison

illu

stra

tion.

Cre

ature

Feat

ure

s: C

om

pari

ng A

nato

my



7Ac

tivity

182

2 Consider This Dr. Gingerich’s original article about Rodhocetus did not include information

about its tail. At that time, no tail for the fossil had been discovered. Try to predict what kind of tail belongs on this ancient whale. Consider the informa-tion given below. Then draw the tail on the partial Rodhocetus skeleton on the Creature Features: Comparing Anatomy sheet. Explain why you think this is the likely tail for this animal.

Fish and sharks have a finned tail that propels them forward by moving in a side-to-side fashion. Dolphins, like all whales, have a fluked tail that moves in an up-and-down motion.

Lind

a Al

lison

illu

stra

tion.



7

Activ

ity

183

PART FOURBe a science reporterWrite a short news story about whales. Tell your readers about new fossil discover-ies from Pakistan that suggest whales are related to animals that once lived on land. Based on what you have learned, explain how you think a whale could have an ances-tor that lived on land.

P.S. Don’t forget the headline.


whales: walking into activity the past - national...

Documents