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Timeline 201.3 to 145 Million Years Ago Jurassic – Land of Giants

Jurassic landscape
Gerhard Boeggemann This painting illustrates a typical Jurassic scene based on fossils found in what is now Lower Saxony in Germany. The largest dinosaur is a brachiosaurus, accompanied by several iguanadons and two composthagnus. Notice the tiny archaeopteryx perched on the deadwood to the lower right?

The Jurassic Period began 201.3 million years ago following the evolution of the first dinosaurs in the last era of the Triassic. However, now was the time when the reign of the dinosaurs would truly reach its golden age. The Jurassic was a time when the largest and most magnificent animals that have ever existed roamed the Earth.

 

For 31 million years, dinosaurs had been evolving at an unprecedented rate, filling the empty niches left behind after the catastrophic Permian-Triassic extinction. Rising to dominance throughout the Late Triassic, the dinosaurs were about to become larger and larger in a warming, high-oxygen world.

The Jurassic Period presents the middle of the Mesozoic Era, the time when some of the most iconic dinosaurs of all time, such as stegosaurus, diplodocus and brachiosaurus lived.

Highlights of the Jurassic

  • Largest dinosaurs evolve
  • Major maritime radiation
  • First ceratopsians evolve
  • Pangaea supercontinent splits up
  • Missing link between dinosaurs and birds appears
  • 160 million years ago: The mi-go set up a mining operation on Earth. The Elder Things try to battle them in space, but find they have devolved so much that they can no longer do so. The mi-go eventually control much of the northern portion of Earth. 
  • Some mi-go settle in the land that will become Mu, and worship Ghatanothoa.
  • The mi-go also bring with them two objects, later known as the Black Seal of Iraan and the Shining Trapezohedron.
  • 150 million years ago: The Great Race of Yith foils a Yekubian invasion attempt. Sometime thereafter, the tablets later known as the Eltdown Shards, which record this event, are buried in the land that will one day become the Kingdom of England.

Mass Extinction Redefines the Path of Marine Evolution

Ichthyosaurus Heinrich Harder
Heinrich Harder

The dolphin-like ichthyosaurus lived among sea crocodiles and plesiosaurs throughout the Jurassic Period.

The Jurassic Period began following the Rhaetian mass extinction, one of the five biggest of such events in the history of the Earth. Many of the larger amphibians disappeared as the dinosaurs and early crocodiles took over.

Although a third of all marine creatures had disappeared by the beginning of the Jurassic, marine reptiles were about to go through one of the most important stages in their evolutionary history. Plesiosaurs (lizard-like) and ichthyosaurs (fish lizards), which had already been present for millions of years, would now move in to occupy the niches left behind by the casualties of the Rhaetian extinction and become the dominant animals of the Earth’s oceans.

One of the most iconic marine reptiles of the Early Jurassic was the ichthyosaurus.

Pelagosaurus, the lizard of the open sea, was a crocodyliform, a relative of ancient crocodiles. It grew up to an estimated 10 feet (3 metres) long.

Near the end of the Early Jurassic, joining the plesiosaurs and ichthyosaurs, was a group of crocodylomorphs named thalattosuchia, which literally means ‘sea crocodile’. Although they themselves are not direct ancestors to modern crocodiles, they formed a closely related and, for a time, a highly successful group. Among their many members were the long, slender and very fast swimmer teleosaurus and the 33-foot-long (10 metres) machimosaurus, the largest member of this family of marine predators.

Heavily Armed Herbivores and Lethal Predators Battle for Dominance

On display in London’s Natural History Museum, Sophie is the world’s most complete stegosaurus specimen, in spite of being 150 million years old. 

While many groups had perished during the Triassic-Jurassic mass extinction, dinosaurs managed to escape relatively unscathed. Their dominance over terrestrial ecosystems strengthened yet still. Herbivorous families grew larger, developing protective spikes and plates to fend off predatory dinosaurs such as the coelophysoids, some of which could grow up to 20 feet (6 metres) in length.

Of course, the most iconic of all these well-protected beasts was the stegosaurus, which means ‘roof lizard’. The first stegosaurs appeared around 165 million years ago during the Mid Jurassic. The largest of the three species so far identified weighed over 2.4 tonnes. Adorned with a lavish array of spikes and plates across its back, tail and hips, this animal was more than capable of standing its ground against many of the predators of the time.

Allosaurus was one of the dominant terrestrial predators of the Jurassic, with the largest reaching lengths of up to 40 feet (12 metres).

During the Late Jurassic, stegosaurus shared an environment with allosaurus, the apex terrestrial predator of the time. Fast and agile creatures with razor-sharp teeth, allosaurus was one of the few animals that would have posed a serious threat to stegosaurus.

The Late Jurassic also saw the appearance of the first ceratopsians, the group to which the Cretaceous triceratops belongs. However, the very first ceratopsians did not look much like the iconic triceratops, aside from their parrot-like beaks. 

Sauropod Dinosaurs Giants Roam the Land

Seismosaurus was the largest of all diplodocids, another extremely successful group of herbivores that evolved during the Mid- to Late Jurassic were the ornithopods. These herbivorous dinosaurs grew larger as they adapted to the predatory environment of the Jurassic. The largest of these was shantungosaurus.

The largest dinosaurs were the sauropods, among the mightiest and most incredible of all the animals that have ever lived. Diplodocids, of which diplodocus is the most famous genus, were by far the largest of the Jurassic sauropods.

Ancient Wings Take to the Skies

Since the Late Triassic, pterosaurs dominated avian niches in almost all areas of the world. A unique and highly successful group of flying reptiles throughout the Jurassic, pterosaurs continued to grow larger in size and number, paving the way for complete dominance of the skies in the Cretaceous Period that would follow.

Archaeopteryx, which lived around 150 million years ago during Late Jurassic, looked much like a bird, it had a beak  and was covered in plumage. The pigeon-sized creature was just as much dinosaur as it was a bird, with teeth, claws on its wings and a bony tail.

Conclusion

By the end of the Jurassic, some of the largest and most magnificent dinosaurs that ever existed ruled over the Earth. Early crocodiles, lizards, frogs, turtles and the direct ancestors to birds all called the warm Jurassic world home. Vast redwood forests, home to some of the largest trees that have ever existed, spanned millions of square miles, their foliage fed upon by colossal beasts such as giraffatitan.

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