Paleozoic and Mesozoic Eras: Key Events and Extinctions

Paleozoic Era

541-252 million years ago; includes Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian

Mesozoic Era

252-66 million years ago; includes Triassic, Jurassic, and Cretaceous

Pangea

Supercontinent formed during the late Paleozoic

Panthalassic Ocean

Massive ocean covering more than 50% of Earth's surface during the Permian

Carboniferous Period

Period known for coal swamps, lycopod forests, and giant insects

Permian Period

Last period of the Paleozoic; ended with the largest mass extinction

Lycopod forests

Coal-forming swamp forests during the Carboniferous

Coal formation

Trees buried in low oxygen swamp environments and compressed into coal over time

Gymnosperms

Seed-producing plants with cones

Amniotic egg

Egg adapted for land reproduction

Why were amniotic eggs important?

Allowed animals to reproduce on land without returning to water

Giant insects

Occurred during the Carboniferous due to high atmospheric oxygen

Meganeura

Giant dragonfly-like insect with a 68 cm wingspan

Amphibians in Paleozoic

Large because there were few land predators and oxygen was high

Sharks in late Paleozoic

Diversified and became important predators in food webs

Crinoids

Marine organisms that reached peak diversity in the late Paleozoic

Alleghenian orogeny

Mountain building event during the Permian

Antler Mountains

Ancient mountains that formed parts of Nevada and Idaho

Snowball Earth

Hypothesis that Earth nearly froze over during late Carboniferous

Permo

Triassic extinction - Largest mass extinction; "The Great Dying"

The Great Dying

Permo-Triassic extinction that killed about 96% of species

Asteroid impact extinction mechanism

Dust blocks sunlight, wildfires release CO2, acid rain, climate change

Evidence for asteroid impact

Iridium anomaly, shocked quartz, crater, fern spore spike

Iridium anomaly

High iridium concentrations linked to asteroid impacts

Shocked quartz

Quartz deformed by intense pressure from impacts

Fern spore spike

Large increase in fern spores after extinction events

Volcanism extinction mechanism

CO2, ash, and gases alter climate

Large Igneous Province (LIP)

Massive volcanic region producing huge lava flows

Deccan Traps

Large volcanic province in India linked to K-Pg extinction

Sea level regression

Falling sea levels exposing continental shelves

Plate tectonics extinction mechanism

Changes climate, sea level, and habitats

Climate change extinction mechanism

Global warming or cooling causing environmental stress

Gamma ray burst hypothesis

Hypothetical extinction cause involving radiation destroying ozone

"Murder on the Orient Express" hypothesis

Multiple causes contributed to mass extinction

Triassic Period

Earliest period of the Mesozoic

Jurassic Period

Middle period of the Mesozoic

Cretaceous Period

Last period of the Mesozoic

Pangea breakup

Began during the Triassic and led to modern continents

Laurasia

Northern landmass formed after Pangea split

Gondwanaland

Southern landmass formed after Pangea split

Atlantic Ocean formation

Created by rifting between North America and Africa

Terrane accretion

Process where crustal fragments attach to continents

Sonomia

Terrane accreted to western North America

Golconda

Terrane accreted to western North America

Franciscan

Terrane associated with western North America

Ammonoids

Marine organisms that recovered after the P-T extinction

Hexacorals

Simple corals similar to modern coral

Conodonts

Extinct eel-like organisms with tooth-like structures

Brachiopods

Marine organisms with two shells

Stalked crinoids

Crinoids attached to seafloor by stalks

Placodonts

Triassic marine reptiles

Nothosaurs

Triassic marine reptiles

Cycads

Mesozoic seed plants

Ginkgoes

Ancient seed plants still alive today

Conifers

Gymnosperms related to pine trees

Lystrosaurus

Common Triassic land animal after the P-T extinction

Why is Lystrosaurus important?

It dominated ecosystems after the P-T extinction

Therapsids

Group leading to mammals

Morganucodon

Early mammal-like animal

Angiosperms

Flowering plants

Relationship between bees and angiosperms

Symbiotic pollination relationship

Rudists

Reef-building clam/oyster organisms in the Cretaceous

Belemnites

Squid-like marine cephalopods

Teleost fish

Advanced bony fish

Mosasaurs

Marine reptiles related to snakes

Plesiosaurs

Long-necked marine reptiles

Ichthyosaurs

Dolphin-like marine reptiles

Pterosaurs

Flying reptiles but NOT dinosaurs

Dinosaurs

Archosaurs with erect posture

Definition of dinosaur

Common ancestor of Triceratops and modern birds plus descendants

Diagnosis of dinosaur

Characteristics used to identify dinosaurs

Erect locomotion

Legs positioned underneath body

Sprawling locomotion

Legs positioned to the sides of body

Synapsids

Amniotes with one skull opening behind eye; includes mammals

Diapsids

Amniotes with two skull openings; includes reptiles and dinosaurs

Archosaurs

Group including crocodiles, dinosaurs, pterosaurs, and birds

Monophyletic group

Group containing ancestor and all descendants

Definition vs diagnosis

Definition = evolutionary relationship; diagnosis = identifying traits

Mammals in Mesozoic

Small early forms similar to monotremes

Cretaceous

Paleogene extinction - Extinction that killed non-avian dinosaurs

Evidence for K

Pg asteroid - Chicxulub crater, iridium anomaly, shocked quartz

Chicxulub crater

Asteroid impact crater linked to K-Pg extinction

Why did inland Permian regions become dry?

Large supercontinent limited ocean moisture inland

Why were giant insects possible?

High oxygen concentrations allowed more oxygen delivery

Why was erect posture useful?

Improved movement and efficiency on land

Mass extinction

Event causing widespread global species loss

Superposition

Oldest rock layers are at the bottom

Original horizontality

Sediments originally deposited flat

Cross

cutting relationships - Features cutting through rocks are younger

Faunal succession

Fossils appear in predictable order

Carbon cycle

Processes adding and removing CO2 from atmosphere

Mechanisms that add CO2

Volcanism, respiration, burning fossil fuels

Mechanisms that remove CO2

Photosynthesis, weathering, ocean absorption

Triassic climate

Intense weather due to giant supercontinent

Why could species move easily across Pangea?

Few mountain barriers and connected landmass

Mass extinction recovery

Ferns and fungi often recover first after extinctions