Chapter 3: Fossils and the diversity of lifefaculty.chas.uni.edu/~groves/EHCh03lecture.pdf · Earth History, Ch. 3 1 Chapter 3: Fossils and the diversity of life • Art objects •

Earth History, Ch. 3 1

Chapter 3:

Fossils and the diversity of life

• Art objects

• Incredible variety

– From “nanno” scale (0.001 mm) to gigantic

– From bacteria to T. rex and everything in between

• Objects of scientific study

– Age dating

– Environmental indicators

– Objective record of evolution


Fossils and the diversity of life

• Our knowledge of past life is derived

mostly from fossils

• Fossil = the preserved remains or traces of a

once living organism

– Usually thousands or millions of years old (if it

still smells, it ain’t a fossil)


Fossil preservation

• “Hard parts” are easily preserved

– Bones, teeth, shells or other skeletal material

• Soft tissue is rarely preserved

– This requires a burial environment in which there is no

oxygen for bacteria

• Permineralization is the filling in of void spaces

with minerals

– Spaces within plant cells can be filled with chert to

form petrified wood


Fossil preservation (continued)

• A mold is a three-dimensional negative imprint of an organic structure (e.g., press your fist into clay)

• A cast is a filled-in mold—it’s an exact replica of the original structure, but without the original composition

• An impression is a two-dimensional imprint, like a very shallow mold (e.g., imprint of a leaf in mud)

• A trace fossil is the preserved evidence of animal activity (e.g., tracks, trails, burrows)


Completeness of the fossil record

Death

Scaveng-

ingDecay

of soft

tissues

Decreasin

g p

robab

ility

100%

?%

Continuous removal of “potential” fossils

The probability of preservation depends on the anatomy and habitat of the

organism—marine organisms with hard parts are most likely to be preserved

Abrasion

And

transport

BurialFinal

Preser-

vation


Taxonomy = the science of classification

and evolutionary relationships among groups

• Groups of organisms are called taxa

(singular, taxon)

• “Natural clusters” of taxa are called clades

– A clade is a group of taxa that share a single

common ancestor


• The taxonomic hierarchy has seven levels

Kingdom (e.g., Animalia)

Phylum (e.g., Chordata)

Class (e.g., Mammalia)

Order (e.g., Primates)

Family (e.g., Hominidae)

Genus (e.g., Homo)

Species (e.g., sapiens)

Taxonomic hierarchy

Incre

asi

ng i

nclu

sive

ness


Clades

Morphology continuum Morphology continuum

tim

e


How are evolutionary

relationships known?

• “Cladistics” is the science of inferring

genealogical relationships among groups of

organisms

• “Cladogram” is a diagram that depicts

inferred genealogical relationships


Cladistics

• All living things are

related (like cousins)

• Any two taxa share a

common ancestor

ASSUMPTIONS

memy

cousins

grandpagrandma

mysister

myparents


Cladistics

Branch tips are taxabeing investigated

Node representscommon ancestor


Cladistics

When more than two taxa are being considered,there are multiple possible branching arrangements

Two taxa are considered to be closely related if they share derived traits that are not present in the third taxon


Cladogram of vertebrates

inve

rtebr

ates

Jawle

ss fi

sh

Shark

s, ra

ys

amphi

bian

s

Bony

fish

mam

mal

s

Turtle

s, c

rocs

birds

origin of vertebral columnVertebrata

origin of jaws with teeth; paired appendagesGnathostomata

origin of bony skeleton

Osteichthyes

Tetrapodaorigin of limbs

Amniota

Reptilia

origin of amniotic egg

origin of skull fenestrae


The Six Kingdoms


Prokaryotes vs. Eukaryotes

• Prokaryotes lack a well defined cell

nucleus and intracellular organelles

• Eukaryotes possess cell nucleus and

specialized organelles


Prokaryotes

• Archaeobacteria are the most primitive life

forms, probably ancestral to all other life

forms—some can tolerate extremely high

temperatures and hostile chemical

environments; others can live in the absence

of oxygen

• Eubacteria are slightly more advanced—

some are capable of photosynthesis


Stromatolites(built by Eubacteria)

Bacterial filaments

Modern stromatolites

Precambrian stromatolites


Protists

• Single-celled or simple

multicellular organisms,

including:

– Algae

– Dinoflagellates

– Diatoms

– Calcareous nannoplankton

– Radiolarians

– Foraminifera

The preserved microfossilsof protists are extremelyuseful for dating sedimentaryrocks.


Protists

dinoflagellate

Calcareous

nannoplanktondiatoms


Protists

Planktonic foram

Radiolarians


Fungi

• Fungi are primitive organisms that typically absord their food from dead plants and animals

– Mushrooms

– Yeasts

• Fungal spores are readily preserved—when they occur in great concentrations they may signal a catastrophic event


Plants

• Non-vascular plants lack conductive tissue and reproduce by means of spores

– Mosses

• Vascular plants possess conductive tissue and reproduce by means of spores or seeds

– Ferns

– Gymnosperms (e.g., conifers)

– Angiosperms (flowering plants)

• Because their tissues are relatively tough, vascular plants have a superb fossil record!!


Plants

Psilotum, the

simplest living

vascular plant


Animals

• Sponges are primitive animals whose cells

are not organized into tissues

• Cnidarians have simple tissues—an inner

and outer body layer

– Jellyfish

– corals


Sponges


Cnidarians

(corals, jellyfish)


Coelomates are more advanced

animals that possess a body cavity

• Segmented worms

• Arthropods (jointed appendages)

– Trilobites (extinct)

– Crustaceans (crabs, shrimp, lobsters)

– Insects (you know ‘em)


Segmented worms; Arthopods


Coelomates (continued)

• Mollusks

– Cephalopods (octopus, squid, Nautilus)

– Gastropods (snails)

– Bivalves (clams, oysters, mussels)

• Brachiopods

– Lampshells

• Bryozoans

– “Moss animals”


Mollusks


Bryozoa


Brachiopods


Coelomates (continued)

• Echinoderms

– Starfish

– Sea urchins

– Crinoids (“sea lillies”)

• Chordates

– Fish

– Amphibians

– Reptiles

– Birds

– Mammals


Echinoderms

Sea urchin

Crinoid

(“sea lily”)


Chordates

Amphioxus


Chordates

Documents

Chapter 3: Fossils and the diversity of lifefaculty.chas.uni.edu/~groves/EHCh03lecture.pdf · Earth History, Ch. 3 1 Chapter 3: Fossils and the diversity of life • Art objects •