Mesozoic Era

Cretaceous Period (146 MYA - 65 MYA)
Earth during the Cretaceous Period
Earth during the Cretaceous Period


Three Major points

  1. Numerous evolutionary radiations occurred during the Cretaceous.
  2. A major extinction occurred at the end of the period.
  3. 85% of all species died in the End-Cretaceous (K-T) extinction

Life and animals

  • This period gives us some of the most beloved dinosaurs of modern days.
  • The Cretaceous period saw marked the first time flowering plants began to appear.
  • Oldest knows ants and butterflies begin to appear.
  • Reptiles were largest marine carnivores.
  • Decline of the brachiopods (may be related to diversification of predators)
  • Modern types of crabs appeared
  • The Tyrannosaurus lives during this period.
  • In the ocean all the large reptilian swimmers (mosasaurs, plesiosaurs and giant turtles) all disappeared.

Localities, Global setting and the environment
  • High sea levels worldwide.
  • Continents began to move toward their present configuration.
  • Atlantic Ocean widened.
  • Gondwanaland breaks up.
  • Temperatures on earth were much warmer. No glaciers.

The K-T Extinction

  • Second largest mass extinction in Earths history.
  • Most of the large vertebrates on earth died out. This includes the sea, air and land.
  • Most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians were primarily unaffected by the End-Cretaceous mass extinction.
  • Main theory that explain the K-T extinction: asteroid collided with earth.

Asteroid collides with earth

  • This large impact would cause the earth to be engulfed in a large dust cloud. This would cause sunlight to be blocked.
  • Acid rain could be produced.
  • Location of crater is said to be located in the east coast of Yucatan, Mexico.



Jurassic Period (208 MYA - 146 MYA)

Earth during the Jurassic Period
Earth during the Jurassic Period

At the beginning of the Jurassic Period, the super-continent Pangaea continued to break away. What was a hot and dry climate now gave Pangaea a humid and drippy subtropical feel.

external image jurassic-landscape.jpg

In the Ocean:
external image plesiosaurus_lebensbild+-+Carl+Buell.jpg

The oceans were filling up with more life, and at the top of the ocean were the Plesiosaurs along with giant marine crocodiles, sharks, and rays.

Download now
Download now

Life in the ocean was diverse, going from fishlike ichtyosaurs and squidlike cephalopods to coral reefs, sponges and snails to the free floating plankton.

On Land:

The Jurassic Period was known as the Age oft the Ruling Reptiles. Because of the green and lush vegetation most dinosaurs were HUGE!

Brachiosaurus- 52ft tall, 85ft long
Brachiosaurus- 52ft tall, 85ft long
Ceratosaurus and Stegosaurus (20 ft tall)
Ceratosaurus and Stegosaurus (20 ft tall)

Camarasaurus (66ft long) & Allosaurus  (36ft long)
Camarasaurus (66ft long) & Allosaurus (36ft long)

Diplodocus (88 ft long)
Diplodocus (88 ft long)

The Sky:


In the Late Jurassic Period, the earliest known bird took to the skies. It is believed that the Archaeopteryx evolved from an early coelurosaurian dinosaur.

Rhamphorhynchus  (Pterosaur)
Rhamphorhynchus (Pterosaur)

However, the skies were not empty, the Archaepteryx had to compete for airspace with ptersosaurs, the flying reptiles that had been buzzing the skies since the Late Triassic Period

There was also many insects, this included leafhoppers and beetles.

While the dinosaurs roamed the earth, many of Earth's earliest mammals scurried around their feet, not knowing that they would dominate the earth once the dinosaurs get wiped out during the end of the Cretaceous Period.



Triassic Period (245 MYA - 208 MYA)
Earth during the Triassic Period
Earth during the Triassic Period
The Triassic period is the first phase of the Mesozoic era. The Triassic Period is known as "the beginning of the dinosaurs."

Climate and Geology

The supercontinent, Pangaea, at the start of the Triassic period had a hot and dry climate. Desert terrains covered most of the land as mountains formed.


No dinosaurs were present until late in the Triassic period. New species arose, such as, reptiles, amphibians, frogs, turtles, lizards and crocodiles. The first mammals appeared like the Eozostrodon. Also, Pterosaurs, flying reptiles, were introduced.
external image papo_ptero.JPG

Image: Computer rendering of fleeing nothosaurs
Image: Computer rendering of fleeing nothosaurs

How did it end?

The Triassic period ended with a mass extinction and volcanic eruptions which caused the super continent, Pangaea, to drift apart. After the extinction and land shifting, new niches were formed. This allowed for the development of dinosaurs…