evolutionary patterns, rates, and trends lecture 23

Evolutionary Patterns, Rates, and Trends

Lecture 23

Fossils

• Recognizable evidence of ancient life

– Fossilized hard parts (most

common)

– Trace fossils (indirect evidence)

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Fossils and the Great Flood!Fossils and the Great Flood!

• Fossils of seashells have been found in Fossils of seashells have been found in

rock layers high in the mountainsrock layers high in the mountains

• How did they get there?How did they get there?

• Initial explanation was that they had been Initial explanation was that they had been

deposited during the biblical flooddeposited during the biblical flood

Evidence of Past Life

• It all began really in the 1700s - mining, tunneling, etc.

• Excavations unearthed similar fossil sequences in distant places

• Scholars began to view these findings as evidence of the connection between Earth history and the history of life

Fossilization

• Organism becomes buried in ash or sediments

• Rapid burial and a lack of oxygen aid in preservation

• The organic remains become infused with metal and mineral ions

• The only way we know anything at all about prehistoric life is through fossils.

• Some people refer to specimens of dinosaurs as "dinosaur bones", but in fact, they are not.

• No organic material can remain unchanged for millions of years.

• That is why, the only pieces of the past that survive to be looked upon by human eyes, do so as rocks, or fossils, as they are called when they came from living organisms.

• So really, there are no dinosaur bones left anywhere, just the ones that have been turned to stone.

How do things turn to stone, or become fossilized?

• First of all, a very small amount of prehistoric life got fossilized.

• In order for this phenomenon to take place, conditions had to be exactly right.

• It was just like winning the prehistoric lottery.• Only the hard parts of an organism can

become fossilized, such as teeth, claws, shells, and bones. The soft body parts are usually lost, except for in very special conditions.

• There are many ways for an organism to get preserved, but lets explain the general way in which most fossils form.

• First of all, fossils only occur in sedimentary rock, no others.

• Here is a basic example of what happens when fossilization occurs. – An organism, let's just say, a dinosaur,

dies. – Their flesh and other tissues is probably

eaten by carnivorous animals, leaving just the bones.

• Let's say, just by chance, that this whole ordeal took place in an area with lots of sand, very near to a river.

• Let's also say that the bones were left undisturbed just long enough for the wind to blow sand and sediments over top of them, causing them to lie a little bit underground.

• Over the years, and we mean thousands of years, the sediments slowly pile up over top of the bones, until they are buried far underneath the ground.

• Let's say the river floods or changes it's course too, and the land over the top gets covered in water.

• While this is going on, the minerals in the bones, calciums and hydroxyapatite, get replaced, one by one, with the minerals in the sand.

• Due to the great pressure over top, the lower levels of sediment get pressed together to form sedimentary rock, with the bones still in it.

• Eventually, millions of years pass by, and there is no organic material left in the bones, they are now solid rock, and are buried deep below the surface, incased in sedimentary rocks.

• One day, someone is digging deep into a quarry, and notices these bones, now fossils.

Stratification

• Fossils are found in sedimentary

rock

• This type of rock is formed in layers

• In general, layers closest to the top

were formed most recently

What Do Fossils Tell Us?

• As a result of mutations, natural selection, and drift, each species is a mosaic of ancestral and novel traits

• All species that ever evolved are related to one another by way of descent

Radiometric Dating

after two half-lives

after one half-lives

parent isotope innewly formed rock

Geologic Time Scale

• Boundaries based on abrupt transitions in fossil record

• Correspond to mass extinctions

• Archean eon (oldest interval)

• Proterozoic eon

• Paleozoic era

• Mesozoic era

• Cenozoic era (most recent)

Macroevolution

Macroevolution can be defined simply as evolution above the species level



Microevolution takes place over a number of generations within speciesi. e. the TICK and Anti-tick Shampoo example last lecture

Continental Drift• Idea that the continents were once joined and

have since “drifted” apart

• Initially based on the shapes

• Pangea: theoretical supercontinent



Evidence of Movement

• Evidence cited from glacial deposits and fossils

• Later was discovered that magnetic orientations in ancient rocks do not align with the magnetic poles

• Discovery of seafloor spreading provided a possible mechanism

Plate Tectonics• Earth’s crust is fractured into plates

• Movement of plates is driven by upwelling of molten rock at mid-oceanic ridges

• As seafloor spreads, older rock is forced down into trenches

Forces of Change

island arc oceanic crust oceanic ridge trench continental crust

subducting plate

athenosphere(plastic layer of mantle)

hot spot

lithosphere(solid layer of mantle)

Gondwana

• Supercontinent preceding Pangea

• Same series of glacial deposits, coal seams, and basalt are found in Africa, India, Australia, and South America

• Antarctica contains same fossils as other southern continents

Changing Land Masses

10 mya65 mya260 mya420 mya

Comparative Morphology

• Comparing body forms and structures of

major lineages

• Guiding principle:

– When it comes to introducing change in

morphology, evolution tends to follow the

path of least resistance

Morphological Divergence

• Change from the body form of a common ancestor

• Produces homologous structures that may serve different functions

Morphological Divergence

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STEMREPTILE

PTEROSAUR

CHICKEN

BAT

PORPOISE

PENGUIN

HUMAN

Morphological Convergence

• Individuals of different lineages evolve in similar ways under similar environmental pressures

• Produces analogous structures that serve similar functions

body wall (exoskeleton)

strong membrane (extension of wall)

wing veins

Comparative Development

• Each animal or plant proceeds through a

series of changes in form

• Similarities in these stages may be clues

to evolutionary relationships

• Mutations that disrupt a key stage of

development are selected against

Developmental Changes

• Changes in the onset, rate, or time of

completion of development steps can

cause allometric changes

• Adult forms that retain juvenile

features

Proportional Changes in Skull

Chimpanzee

Human

Kansas State School Board

• For the sake of their children… • Best to leave both politics and religion out of

schools (per the instructions of the founders of the US).

• Teach science in science classes and not religion.

• Don’t be afraid of the scientific facts • Let each family decide what they should

believe

evolutionary patterns, rates, and trends lecture 23

Documents

dinosaur bones

fossils form

fossils of seashells

millions of years

organic material

solid rock

sedimentary rocks

prehistoric life