Mesozoic.

The

Mesozoic

Era.

The Mesozoic Era spans 183 million years, beginning with the Triassic period 248 million years ago, and finishing with the end of the Cretaceous period 65 million years ago.
Period 65 Million years

Cretaceous

The Cretaceous period, which begins 144 million years ago and spans 79 million years. It is the closing period of the Mesozoic era, and is also the longest period of that era.

During the Cretaceous period reptiles still ruled the land. Giant Sauropod dinosaurs, such as Rebbachisaurus, continue to survive although they become rare in some regions.
Plated dinosaurs, such as Kentrosaurus, barely survive from the Jurassic period, but armoured dinosaurs, which developed massive armour plates and spines, and horned dinosaurs, such as Triceratops which reached a length of 8 metres (26 feet), both flourish.
The largest know land dwelling carnivore, the well known dinosaur Tyrannosaurus which reached a length of 12 metres (40 feet), lived during the end of the Cretaceous period.
Flying reptiles, including the Pterosaurs such as Pteranodon, soar in the skies.

Amphibians are represented only by existing groups such as frogs and salamanders. Lizards become common, including the giant aquatic predatory Mosasaurs.
Also in the seas reptiles such as turtles are to be found, including the giant Archelon. Plesiosaurs continue to prosper, but Ichthyosaurs decline early in the Cretaceous period.
Sponges, Bivalves and Echinoids are abundant, while Ammonites and Belemnites both begin to decline in numbers. Crustaceans such as lobsters become common.
Modern teleost fishes become widespread towards the end of the period, and modern sharks appear during this time. Rays and skates were also present in the Cretaceous seas.

Flowering plants, or Angiosperms, first appear.

The end of the Cretaceous period heralds a time of mass extinction for many groups of animals.
The dinosaurs, marine reptiles such as the Plesiosaurs, Ichthyosaurs and Mosasaurs, and the flying reptiles including the Pterosaurs all become extinct by the end of the Cretaceous period, along with invertebrates such as the Ammonites and Belemnites.

The name Cretaceous is derived from Creta, the Latin word for chalk, extensive deposits of which were laid down in Europe and parts of North America during this period.

Tyrannosaurus.

Tyrannosaurus

Pteranodon.

Pteranodon

Triceratops.

Triceratops

Kentrosaurus.

Kentrosaurus

Rebbachisaurus.

Rebbachisaurus

Mosasaurs.

Mosasaurs

Archelon.

Archelon

144 Million years

Jurassic

The Jurassic period begins 213 million years ago and spans 69 million years. It is the second of the three Mesozoic periods.

On the land dinosaurs thrive and they begin to attain enormous sizes towards the end of the Jurassic period. The largest of these dinosaurs were the Sauropods, including Diplodocus and the massive Brachiosaurus which reached a length of 25 metres (80 feet) and is estimated to have weighed up to 100 tonnes.
Dinosaurs from early in the Jurassic period include Scelidosaurus, which reached a length of 4 metres (13 feet). Later in the period more specialized forms of plated dinosaur appeared, such as Stegosaurus, which attained a length of up up 9 metres (30 feet).
Giant carnivorous dinosaurs, such as Megalosaurus, become widespread from the middle of the Jurassic period onwards.

The first bird, the famous Archaeopteryx, appears in the upper Jurassic, and mammal-like reptiles become extinct during this period. The forests contain plants such as ferns, cycads, tree ferns and towering conifers.

In the seas marine reptiles such as Ichthyosaurs and Plesiosaurs become common, while invertebrate life is dominated by the Ammonites and Belemnites.
Sponges, Crinoids, Echinoids are also common, and Crustaceans such as the first crabs make their appearance. Brachiopods begin to decline, while Bivalves become more numerous.

The Jurassic period is named after the Jura Mountains on the border of France and Switzerland, where strata of this age is very well presented.

Archaeopteryx.

Archaeopteryx

Stegosaurus.

Stegosaurus

Scelidosaurus.

Scelidosaurus

Ichthyosaurs.

Ichthyosaurs

Ammonites.

Ammonites

213 Million years

Triassic

The Triassic period begins 248 million years ago and spans 35 million years. It is the first period of the "Age of the Reptiles" - the Mesozoic era.

During the Triassic period reptiles flourished with new groups appearing including crocodiles, turtles, Phytosaurs, such as Rutiodon, the mollusc-eating Placodonts, such as Placodus, Pterosaurs, Plesiosaurs, Ichthyosaurs, Nothosaurs, such as Nothosaurus, and the Protorosaurs, such as the the long necked Tanystropheus.
Mammal-like reptiles, such as Lysrosaurus, continued to survive from the Permian period.
Early dinosaurs appeared by the middle of the Triassic period, and the first true mammals, such as the small Megazostrodon, had evolved by the end of the period.

Plants such as ferns, cycads, and seed-ferns all flourished.

In the seas the first hexacorals appeared, along with the first Belemnites. The Ammonites evolved from their early ammonoid ancestors the Ceratites at the end of the Triassic period.

The Triassic is named after the threefold series of strata from this period, the Bunter, Muschelkalk and Rhaetic, which occur in southern Germany.

Cycads.

Cycads

Megazostrodon.

Megazostrodon

Lystrosaurus.

Lystrosaurus

Placodus.

Placodus

Tanystropheus.

Tanystropheus

Rutiodon.

Rutiodon

Nothosaurus.

Nothosaurus

248 Million years

 

Caenozoic. Mesozoic. Palaeozoic.

 

Return to the Geological Time Line.