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
Mass Extinction Redefines the Path of Marine Evolution
The Jurassic Period began following the Rhaetian mass extinction, one of the five biggest of such events in the history of the Earth. Among its many casualties were almost all families of ammonites, a group of marine molluscs that evolved 400 million years ago during the Devonian Period. The eel-like conodonts vanished entirely from the oceans while, on the land, many of the larger amphibians also disappeared as the dinosaurs and early crocodiles took over.
Although a third of all marine genera 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.
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
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. Unfortunately, however, stegosaurus probably wasn’t the sharpest knife in the drawer, having a braincase the size of a sheep. It was for this reason that the popular misunderstanding that stegosaurus had two brains came about, one of the most common dinosaur myths of all.
During the Late Jurassic, stegosaurus shared an environment in what is now North America with allosaurus, the apex terrestrial predator of the time. Three species of these theropod dinosaurs have so far been discovered, with the largest one reaching a length of 40 feet (12 metres). Fast and agile creatures with razor-sharp teeth up to four inches (10cm) long, allosaurus was one of the few animals that would have posed a serious threat to stegosaurus.
A common question in the world of dinosaurs is who would win a fight between stegosaurus and allosaurus. I would say probably the latter, with its undoubtedly greater wit and speed. Nonetheless, given the stegosaurus’s lethal thagomizer, allosaurus likely wouldn’t have won the fight unscathed.
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. These relatively small herbivorous ornithischians, such as the recently discovered chaoyangsaurus and yinlong, were all smaller than sheep.
Sauropod Dinosaurs Break All Records as Giants Roam the Land
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. Contrary to popular belief, the pterosaurs were not actually dinosaurs. Instead, they belonged new a unique and highly successful group of flying reptiles that lived right up until the cataclysmic extinction event that also claimed the dinosaurs. 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, however, not least because it still had teeth, claws on its wings and a bony tail.
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.