10-31 Lecture Notes

7/30/2019 10-31 Lecture Notes

1/14

s oryo

e

easege ou no es rom as mewe n s e

slideson

sympatric

speciation

Todays

questions:

. owcanwes u yevo u on s rea es s

.W y

scorro orat ng

ev ence

rom

n epen ent

sourcesofdataimportant?


2/14

Thebasicformofthetetrapod limb:

Hypot es s:t etetrapo m evo ve rom

Four legged, for land mammals.

the lobes of the lobe

finned fish.


3/14

Fossillimbsfromlobefinned

fishandearlytetrapods

Whichhave

the

basic

tetrapod

limbpattern?

W c ave g ts owmany

Whichswam?Crawled?

Walked?


4/14

Phylogenyof

early

tetrapods,basedon

.

Dothesedatasupport

thehypothesis?

Whyor

why

not?


5/14


6/14

Specieswithlobedfinsarefoundinolderstrata(rockbeds)

thanspecieswithlimbs.Dothesedatasupportorconflict

withthefinstolimbshypothesis?Explain.Support because you expect the fins to show up first and be older since

it's an ancestral (basal) trait.


7/14

2.Radiometric

dating

established

the

absolute

ages

of

the

fossilbearingrocks

1. Ratioof

parent

to

daughter

isotope

when

rock

formed

(e.g.initially,volcanicrockshavenoargon40;itisagas

thatbubblesoutofmagma)

2.Decayrate(e.g.rateatwhichpotassium40decaysto

argon40)measuredinhalflives

3.Currentratioofparenttodaughterisotope(e.g.


8/14

onakeyassumption.What

isit?

Specieswithlobedfinsarefoundinrockswitholder

absoluteagesthanspecieswithlimbs.Dothesedata

That the isotopes behaviorsdoesn't change over time?

The data is relative.


9/14

3.Associated

fossils

and

the

nature

of

the

host

rock

supportthehypothesisofanaquatictosemiaquaticto

Rockslaiddowninaquaticenvironmentsaredifferent

t anroc s ai owninterrestria environments;

Findfossils

of

a uatic

versus

terrestrial

or anisms

(algae,landplants)


10/14

4.Comparative

morphology

supports

the

hypothesis

of

homologyinlimbelements

. v v

Studygenesandallelesinvolvedintheoriginofkey

synapomorphies morphologicalinnovations


11/14

The phylogeny in your notes was estimated from skull characters, not

fin or limb characters, why is this important?

-Otherwise the argument it's circular.

-We use skull to have another independent source to help support our

thinking.


12/14

7.Comparisons

with

extant

taxa:

Modernlobefinnedfish(coelacanths)donotusetheir

finsto

crawl.

But

when

they

swim,

they

move

their

fins

inthesamepatternastetrapods movetheirlimbs

whenwalking.

Modernlungfish

can

breathe

air

and

use

their

fins

to

crawlacrossdryingpondsurfaces

Dothesedatasu ortorconflictwiththefinstolimbs

hypothesis?Explain

your

reasoning.

If the lobe-finned fish were able to have a walking motion, it might suggest

that they are able to develop traits. The fins could be used in a walking

motion, so that means they could have been on land and selected for limbs

more fit for walking.


13/14

Whichof

these

seven

sources

of

evidence

do

you

find

mostconvincing,andwhy?

Wh

doscientists

stress

the

im ortance

of

data

that

are

independentandcorroborating?

There is no one piece of evidence that is the most convincing, it's the

entire body of evidence that's convincing.

So it's more reliable. It helps prevent circular reasoning.


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10-31 Lecture Notes