The Mesozoic Era
250 to 65 Million Years Ago
The Mesozoic Era is comprised of three periods:
| Period | MYA1 |
|---|---|
| Cretaceous | 145-65 |
| Jurassic | 200-145 |
| Triassic | 250-200 |
This is perhaps the most famous and familiar era to many people since the Mesozoic is the era of the dinosaurs in all their many fantastic shapes and sizes. At no other time have such enormous creatures roamed the earth and surely no other creatures fire the imaginations of both children and adults worldwide. But the era did not begin so auspiciously. As the Triassic dawned, devastation and death were widespread upon the planet. By the end of the Triassic, the dinosaur era had begun culminating in a menagerie of creatures and plants not seen since the asteroid struck.
Oxygen, Carbon Dioxide and the Atmosphere
- Oxygen levels started out low at the beginning of the Era as
a consequence of the Permian Extinction; however, they plummeted
even lower at the end of the Triassic, instigating another mass
extinction.
- The low oxygen of the Triassic was the lowest ever experienced by Life on Earth.
- Throughout the Jurassic and Cretaceous the levels continued to climb, reaching near-modern levels.
- Carbon dioxide levels,
high at the beginning of the
Triassic, fell quickly, reaching near-modern levels as well.
- From the late Triassic onwards, carbon dioxide continued
to rise, until the Cretaceous when it began a gradual
decline.
- From the late Triassic onwards, carbon dioxide continued
to rise, until the Cretaceous when it began a gradual
decline.
Continents and Oceans
- Pangea, the vast single continent formed in the late
Paleozoic, had begun to break apart early in the
Mesozoice Era.
- By the end of the era, many island continents had formed, including North America, Africa and India.
- The basin of the Atlantic Ocean continued to spread as the continents drifted apart.
- Sea levels were at their lowest levels ever, but by the
Cretaceous the sea levels had risen to the extent that many of
the continents were covered by shallow seas.
Climate
- The arid landscape of the Triassic was eventually replaced by the warm, moist environs of the Jurassic.
- The Cretaceous saw a cooling trend as the glaciers grew once
again at the poles having been absent during the Jurassic.
Nevertheless the Cretaceous remained warmer than today due to
elevated carbon dioxide levels.
- Fossils of dinosaurs can be found at the extreme north
indicating a mild climate.
- Fossils of dinosaurs can be found at the extreme north
indicating a mild climate.
Plant Life
- The sparsity of vegetation in the Early Triassic led to a distinctive lack of coal deposits in the early Mesozoic.
- As carbon dioxide levels climbed, the plants rebounded.
- Some of the Paleozoic species survived and continued on in the Mesozoic, adapting to the changing conditions and reinventing themselves.
- The angiosperms (flowering plants) arrived during this era
and revolutionized everything from the landscape, to the
available habitats for insects, mammals and reptiles, and most
importantly, their diet.
- By the end of the era, they constituted about 90% of all plant types.
Animal Life
- Dinosaurs first appeared in the late Triassic and would come to dominate the remaining periods.
- Mammals
first appeared in the late Triassic, though they remained small
throughout the Mesozoic.
- Some of the significant developments in the mammalian
realm was the appearance of three new reproductive methods.
Even today, the mammalian world is divided into three groups
based on these reproductive methods that emerged in the
Cretaceous:
- Placental mammals
- Marsupials
- Monotremes
- Some of the significant developments in the mammalian
realm was the appearance of three new reproductive methods.
Even today, the mammalian world is divided into three groups
based on these reproductive methods that emerged in the
Cretaceous:
-
Pterosaurs formed another significant branch of life,
appearing in the late Triassic along with their dinosaur
relatives.
- Forming into a variety of species, the continued to grow in size until some species reached gigantic proportions by the Cretaceous.
- Along with the pterosaurs, were the early birds, their best-known representative being Archeopteryx.
- The oceans teemed with life as huge creatures darted through
its waters, including mosasaurs, icthyosaurs, giant turtles and
plesiosaurs.
- Coral reefs flourished in the warm waters, covering enormous stretches of ocean shallows.
- Insects continued to diversify, adapting to new plants and
environments.
- With the appearance of the angiosperms, the insect way of life was revolutionized by the need for pollinization.
- Grasshoppers, flies, ants, bees and wasps are just a few of the new types of insects to appear during this era.
Extinction Events
- The three main extinction events occurred during the Mesozoic era:
the asteroid impact bringing the Era to a close and issuing in a
new way of life.
- Triassic
- Jurassic
- Cretaceous (asteroid impact)
- Triassic
1. MYA = Millions of Years Ago.
