| |
|
|
|
- 7 Humans in Africa
Cretaceous Period
Geologic - The continents, while not in their current positions on the Earth, are shaped much as they are today. South America and Africa separate, and the Atlantic ocean widens. A circum-equatorial sea, Tethys, forms between the continents of the Northern and Southern Hemisphere. The westward movement of North America forms the ancestral Rocky Mountains and the ancestral Sierra Nevada. Sea levels rise, submerging about 30% of the Earth's present land surface.
The global climate is generally warm. The poles are free of ice.
Biologic - Dinosaurs during this time included muttaburrasaurus, quetsalcoatlus, ankylosaurus. Dinosaurs died out towards the end of this period.The first snakes and modern mammals appeared.
Dinosaurs and other large reptiles peak as the dominant vertebrate life form on Earth. Dinosaurs extend their range throughout every continent. Horned dinosaurs are common, while armored
ankylosaurs and spiky nodosaurs are rare.
In the shallow seas, invertebrates live in great diversity. Ammonites are a dominant group. Gastropods,
corals, sea urchins flourish.
The early flowering plants (angiosperms), modern trees, and many modern types of insects evolve.
Near the end of the Cretaceous Period, several mass extinctions occur, including the extinction of five major reptilian groups: dinosaurs, pterosaurs, ichthyosaurs, pleisosaurs, and mosasaurs. Extinctions also occur among ammonites, corals, and other marine invertebrates. |
|