Not Just A Novelty: The Era of Dinosaurs

Dinosaurs roamed planet Earth during the Mesozoic Era, which ran from 248 to 65 million years ago. It was divided into three distinct periods: the Triassic, the Jurassic and the Cretaceous. When the Mesozoic Era began, all of the 7 continents (Asia, Europe, Africa, North America, South America, Australia and Antarctica) were connected into a single landmass known as Pangaea. The continents then began to drift apart due to a series of earthquakes and plates of land moving along fault lines. Scientists have supporting evidence for this theory in similar fossils found in the areas that are thought to have been connected at one point, such as Africa and South America. 

Mesozoic Era (248 - 65 million years ago)

Triassic Period (248 million years ago)

The beginning of the Mesozoic Era is known as the Triassic period. In the Triassic Era, Pangaea was only beginning to break apart. Except for the coastlines, the climate was very dry and arid. Although dinosaurs did exist during the Triassic Period, they weren’t relatively populous. Reptiles, turtles and ichthyosaurs (“fish-lizards”) were much more common. Dinosaurs did begin to expand, though, and were much more prevalent in the Jurassic Period.

Jurassic Period (208 million years ago)

After 40 million years, the Triassic Period became the Jurassic Period which is believed to have been very warm. There was not yet any land at the North or South Pole. Pangaea had already divided into two separate supercontinents: Lauasia, which was comprised of modern day North America, Europe and Asia, and Gondwana, comprised of what is now Antarctica, South America, Africa and Australia. Most of the dinosaurs appearing in the hit 1993 film Jurassic Park are not actually from the Jurassic period but rather from the Cretaceous period. However, two of the most well-known species were., both the Stegosaurus and the Brachiosaurus.

Cretaceous Period (144 million years ago) 

Beginning 144 million years ago, which was 64 million years after the start of the Jurassic Period, planet Earth moved into the Cretaceous Period. In the Cretaceous Period, Laurasia’s North America separated from Europe and Asia. Gondwana broke into five separate parts, four modern continents as well as what is now India. Climate-wise, it was still incredibly warm. Most of the well-known dinosaurs lived during the Cretaceous period, including the Iguanodon, Ankylosaurus, Velociraptor, Tyrannosaurus Rex and the Triceratops.

Types of Dinosaurs

There are many other forms of life that existed during the Mesozoic Era that were not considered Dinosaurs. Scientists have set in place several rules to identify traits of Dinosaurs.  Dinosaurs lived during the Mesozoic Era only, between 250 - 65 million years ago. Dinosaurs only lived on land, had straight legs tucked below the body, and were reptiles. Because so many fit into this description, scientists began to further categorize Dinosaurs into groups.


Ornithischians first appeared in the late Triassic period but by the early Jurassic, they became so diversified that scientists divided these Dinosaurs into smaller categories for identification purposes. One trait that these types of Dinosaurs share is hip shaped bones that resemble birds. There is the Cerapoda which includes Ceratopsia, Ornithopoda, and Pachycephalosaur. Then, there is also the Thyreophora which includes the Stegosaur and the Ankylosaur. Let’s take a look at each one separately and see how they’re different.



Ceratopsia is a subset of the Ornithischian Cerapoda. Ceratopsians are also known as horned dinosaurs because of beak-like horns found around their mouths. The most famous is the Triceratops which also had a large ridge around the back of its skull. The name Triceratops means “three horned head” and it was an herbivore. Its fossils have been discovered in Colorado and Wyoming. The average Triceratops was thirty feet long and weighed as much as 12000 pounds!


Like Ceratopsians, Ornithopoda are also Ornithiscian Cerapoda. The most famous Ornithopoda, or bird-footed dinosaur, was the Iguanodon. It lived on Earth for tens of millions of year, making its species one of the longest to survive. The Iguanodon, an herbivore, gets its name from its iguana-like teeth. The average Iguanodon was 33 feet tall and weighed 9000 pounds! Fossils have been discovered in various parts of Europe and North America. 


The final of the three Ornithiscian Cerapoda are Pachycephalosaurs, which were herbivores that had incredibly thick skulls with the outside covered in spikes. They were generally only a few meters long and lived from the early Cretaceous period all the way until the end. The most famous was the Pachycephalosaurus which was known as the “thick-headed lizard.” It was the largest Pachycephalosaur at 16 feet with a weight of 1100 pounds. Its dome-shaped skull was likely used for fighting and also for ramming. Pachycephalosaurus fossils have been discovered in various parts of the northern, Midwest United States including Montana, South Dakota and Wyoming.



When people think of dinosaurs, the Colorado-dwelling Stegosaurus is usually one of the first to come to mind. The Stegosaurus is of the Stegosauridae class which is often considered the least intelligent class of dinosaur due to their small heads and brains. Stegosauridae are Ornithiscian, but they are members of the subset Thyreophora. All known species of Stegosauridae were herbivores, but the most notable feature about Stegosauridae is that they have a series of plates running down their backs. It is often thought that the plates were used for protection but that is a misconception. The plates served a different purpose: to regulate body temperature. The average stegosaurus was over 29 feet long and weighed 6000 pounds!


Like Stegosauridae, Ankylosauria are also Ornithiscian Thyreophora. Known as armored dinosaurs, they were all herbivores. The most famous of the classification was the Ankylosaurus, which was one of the last dinosaurs to go extinct. It existed in North America alongside the Tyrannosaurus. To protect itself from such dangerous predators it had sharp spikes all along its body and a hammer-like tail that could be used for fighting. The average Ankylosaurus was 35 feet long and weighed 8000 pounds!


Is a type of dinosaur that is not Ornithischian. They are divided into two categories: Sauropoda and Theropoda. The trait that scientists use to determine which dinosaurs are Saurischian is a pelvic shaped hip - like lizards.


Sauropods were Saurischian dinosaurs that were essentially large herbivores. The most famous Sauropod was the Brachiosaurus, which is recorded as both the largest and the heaviest land animal to have ever been discovered. The average Brachiosaurus was 85 feet long and weighed 160000 pounds. That’s more than twice the height and thirteen times the weight of the T-Rex! Its forelegs were longer than its hind legs which made it look even taller!


Some of the coolest dinosaurs were Theropods. They were Saurischian carnivores with serrated teeth. One Theropod worth noting is the Troodon which is considered the smartest dinosaur, though it was only about as smart as the modern-day possum. Its name means “wounding tooth” and it is known for its hunting ability because it had great eyesight, sickle-shaped claws and it was very fast. The Troodon was only about six feet in height and a slender fifty-five to one hundred pounds!

The Velociraptor is another very famous Theropod because of its appearance in the 1993 film Jurassic Park. Its name means “quick hunter” and it had a very hard, inflexible tail that it used to maintain its balance. It is believed that Velociraptors used their feet to attack their prey. The average Velociraptor was only about five feet tall and weighed as little as sixty-five pounds. Fossils have been discovered in parts of China and Mongolia.

But one cannot discuss Theropods without mentioning the King of the Dinosaurs: the Tyrannosaurus Rex. This “tyrant reptile” lived in the late Cretaceous period and, like the Akylosaurus, was one of the last dinosaurs to die out. The Tyrannosaurus Rex’s head, just its head, was about four feet in length! In total, the dinosaur was 40 feet tall and weighed 12000 pounds. That’s one huge and heavy dinosaur! However, it only had two fingers on each arm.

Mass Extinction

The definition of a mass extinction calls for over 50% of the living species to have gone extinct in a period of less than two million years. The end of the Mesozoic Era is marked by the mass extinction of over 90% of the Earth’s species. There are many theories as to what caused the disappearances during what is sometimes referred to as the K-T Extinction. Perhaps the extinction occurred gradually over millions of years. This is one of the older theories, but still a plausible theory. Another possibility is that the dinosaurs were killed off by a disease. Most forms of life today are susceptible to illness and plagues, and it is therefore plausible that such disease was common during the Mesozoic Era.  Competition has also been considered. There was an increase in the mammal population at the end of the Cretaceous Period. Perhaps competition between dinosaurs and mammals led to their ultimate demise.

The two most common theories of the K-T Extinction are volcanic eruptions and the impact of an asteroid striking the earth. Some believe that volcanic eruptions released enough toxic and heat-trapping gas into the atmosphere that it caused global warming. Alternately, the massive amount of smoke could have blocked the sunlight from reaching the earth. With no sunlight, plants could not survive. Without plants to eat, herbivores would perish, and without herbivores to eat, carnivores would soon follow. The other most widely believed theory is that an asteroid landed in what is now the Yucatan Peninsula. The impact is recorded as the largest in history both on Earth and in the entire solar system. The theory finds that the dust lifted into the atmosphere as a result of the impact would undoubtedly block sunlight for a large portion of Earth in a similar manner to that of volcanoes.

For Further Information on Dinosaurs, Pangaea and the K-T Extinction

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