LECTURE 7: Mesozoic Era248 mya – 65 mya

Periods of the Mesozoic Era

• Triassic – 248 mya-206 mya

• Jurassic– 206 mya-146 mya

• Cretaceous– 146 mya-65 mya

What Significant Events Occurred During the Mesozoic Era?

(248 mya- 65 mya) • Age of Dinosaurs

– Largest animals to have ever walked the earth– Gave rise to birds: today’s only living dinosaurs

• Age of Reptiles– Some started to fly, others went into the sea– First crocodiles, snakes and turtles

• First Mammals• First Birds• First Angiosperms

– Flowering plants

What Plants Survived the 3rd Mass Extinction?

• Less impact on plants than on animals

• Only around 20% of plant species died out

• Instead, the landscape continued to change gradually– Hardy seed-bearing plants replaced spore-

bearing plants as drier environments replaced swampy wetlands during the Mesozoic Era

Why did Plants Survive the Permian Extinction?

• Plants are hardier than animals

• A simple lifestyle – Plants’ basic needs—water, carbon dioxide, and a

few essential nutrients—are always present

• Built-in protection– When confronted with environmental challenges,

plants have their own protective gear. Seeds, for example, can lie dormant for long periods of time until conditions improve

• Part of a fern frond Thaumatopteris braunianaTriassic

• Ferns and other spore-bearing plants were still part of the landscape at the beginning of the Mesozoic Era

But they were not as abundant, diverse, or widespread as seed-bearing plants, such as conifers

• Conifer branches with leavesPagiophyllum

• Triassic Spore-bearing plants such as ferns need wet conditions for sperm to swim to the egg.

But seed-bearing plants such as conifers can thrive in drier habitats because their sperm is transported inside a pollen grain

What Animals Survived the Permian Extinction?

• Only one species out of five tetrapods survived• Every tetrapod to have lived since, including

you, can be traced back to these few survivors• Synapsids, bounced back more quickly than

reptiles or other tetrapods – Mammals descended from these tetrapod

survivors– The most common synapsid fossils found from the

beginning of the Triassic Period are: • Cynodonts

– Mammal-like teeth and may have had hair and whiskers

• Dicynodonts (most Common Triassic Synapsids)– Non-mammalian 2 tusks (Testudines- turtles)

• Cynodont synapsid skull Dadacon isaloi

• Dicynodont synapsid Lystrosaurus

a group of plant-eating synapsids united by their sharp, turtle-like beaks

What Existed in the Triassic Sea?

• Large Giant, Predatory Reptiles

• Sauropterygian– Augustasaurus hagdorni

Early sauropterygians had webbed hands and feet. Over millions of years, hands, feet, and limbs evolved into solid, broad paddles.

Moving its paddles up and down as a bird moves its wings, sauropterygians would swim or “fly” through the water much like today’s sea turtles and penguins do

What was the First Mammal?

• Megazostrodon and Morganucodon - 210 mya– Hair – “Toolkit” of different shaped teeth for different tasks– Small (10-12 cm)

• Early Jurassic MammalMorganucodon oelheri

With large eyes and a long snout, this little mammal may have been a nocturnal hunter with good vision and an acute sense of smell.

What are Archosaurs?

• Appear in the Triassic Period

• Diapsids

• Includes descendents, extinct, and living species: – Dinosaurs (including Birds)– Crocodiles– Pterosaurs

What were the First Dinosaurs?

• Eoraptor lunensis– Small, Bipedal – Carnivore

• Herrerasaurus ischigualastensis

What Happened at the End of the Triassic 200 mya?

• Mass Extinction #4• Caused By Continental Shift/Pangaea Starting to

break apart• On land, volcanic activity led to global warming

– many reptiles:all large crurotarsans (non-dinosaurian archosaurs)

– many of the large amphibians were wiped out • At sea, sea levels dropped, eliminating habitat

for marine animals– 50% of all marine life

• This event vacated ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period

• Pangaea pulls apart

Earth’s continents are constantly—slowly—on the move.

Pangaea assembled completely during the Triassic Period before beginning to break apart in the Jurassic Period

Triassic ReptilesWent Extinct at the End of the Triassic

• Phytosaur reptile Machaeroprosopus andersoni

With their long snouts and sharp teeth, phytosaurs looked, and perhaps behaved, like today’s crocodiles—although they are not closely related

• (Nostrils behind eyes- Crocs nostrils on tip of snout)

What New Predators Existed in Jurassic Seas?

• Ichthyosaur reptileStenopterygius quadriscissus

• One group of marine reptiles, the ichthyosaurs, changed dramatically as they evolved.

They started off looking basically like reptiles with flippers. But over time they became much

more dolphin-like, their form changing as their lifestyle changed

What are Angiosperms?

• Flowering Plants- 140 mya

• Seeds enclosed in Fruits– Archaeanthus

linnenbergeri

– Greek angos, meaning “vessel,” and sperma, meaning “seed”

• Maple and legume (angiosperm) leaves Acer cretaceum

• Gleditsiophyllum aristatum

This leaf on the top belonged to a maple tree. The one on the bottom belonged to a legume, a relative of pea and

bean plants

DINOSAUR DIVERSITY

• 2 Orders

– Saurischia (Lizard- Hipped)

• Theropods –Bipedal carnivores/Bird Ancestors

• Sauropods –Quadripedal herbivores (LARGEST

ANIMALS EVER)

– Ornithischia (Bird-Hipped)

• Mostly Quadrupedal Herbivores

Sauropods

• Brachiosaurus• Argentinosaurus

(largest dinosaur)

Therapods

• First Dinosaurs – Herrerasaurus and Eoraptor

• Tyrannasaurus rex• Deinonychus

Are Birds Dinosaurs?

• Yes!• A group of theropod

dinosaurs called dromaeosaurs (raptors)are among birds’ very closest relatives

• Dromaeosaur skeletons share many things in common with those of birds. Some are easier to see than others

What was the First Bird?

• Archaeopteryx – True Flyer

What happened at the End of the Cretaceous?

• Mass Extinction #5• Wiped out more

than 50% of life on Earth—including all dinosaurs except birds

• Cause is debated– Asteroid– Volcanic Activity