The History of Dinosaurs

For 150 million years, the biggest and more important animals were the dinosaurs. Some were smaller than a chicken, others were as tall as a house.
The climate at that time was much warmer, dry, and the ocean levels were higher. The lands were different and stayed very close to each other. It was called "Pangaea", a single supercontinent. With time, the lands started to gradually move far from each other making earth similar to what it looks like today.

All dinosaurs had long tails to help them with balance. They also had multiple holes in their bones or air sacs to make them lighter. Althought their big size they were relatively light for their size.
Some dinosaurs had feathers and it's speculated that some could fly in some way, but most of them were covered in scales.

The Saurischia and the Ornithischia

The division between the two groups is based on the hip's characteristics.
The Saurischia group contains dinosaurs with a hip bone similar to those of reptiles.
The Ornithischia group contains dinosaurs with a hip bone similar to those of birds.

All Ornithischians were herbivorous and had a type of beak at the front of the maxillae. The Ornithischians were quite rare until the end of the Jurassic period, it was when they evolved and became more numerous.
Their pubis moved pointing behind and this would allow the digestive system to stay near their legs so the organs could be supported.
The first Ornithischians were fabrosaurids. They lived in Africa, Asia, Europe and the Americas. Most of them were very small with half of a human size, and they were very fast. They could walk on four legs, but, except for the Scutelosaurus, probably walked on two legs and used their "arms" to grab food. The teeth was small, leaf-shaped and sharp. The teeth were used to grasp food and cut into smaller sizes. These small dinosaurs later evolved into different creatures of a variety of sizes.

Most Ornithischians herbivores could stand on two legs, while the Saurischian herbivores (sauropods) only walked on four legs.

The Saurischians include the huge herbivorous sauropods and the carnivorous theropods.
Saurischians first appeared in South America about 228 million years ago and rapidly spread across the world. After that, approximately 210 million years ago, a small group of dinosaurs evolved in South Africa and became the herbivorous beaked Ornithischians. Their digestive system also evolved to be bigger so more vegetative food could be stored and more nutrition be extracted.
The first Saurichians to appear were the theropods. They had big heads, strong bites and sharp teeth. The arms were strong enough to grab the prey and the legs usually had big claws.

The Triassic

The Triassic period lasted for 50 million years. It began 250 million years ago and ended 200 million years ago.
There was a single supercontinent called pangaea. Since there was only one continent, there was only one ocean which was called Panthalassa.

The center of the Pangaea was a desert, it was very hot at summer and very cold at winter. Only the most resistent and strong species could survive at these extreme conditions.

The ocean teemed with life, from the tiniest phytoplankton to massive marine reptiles like the Ichthyosaurus.

Before the Triassic, it was the Permian period. The Permian period ended after a mass extinction event known as "Great Dying". It was primarily caused by massive volcanic eruptions in Siberia, known as the Siberian Traps, which released vast quantities of gases, leading to significant climate change and ocean acidification. This event, occurring about 250 million years ago, wiped out over 90% of marine species and 70% of terrestrial species.
Some scientists propose that the volcanic eruptions weakened the ozone layer, increasing harmful ultraviolet radiation reaching the Earth's surface and contributing to the extinction of terrestrial life.

Around 200 million years ago, the Earth experienced a major extinction event that marked the end of the Triassic Period. This extinction was likely caused by massive volcanic eruptions in an area known as the Central Atlantic Magmatic Province (CAMP). These eruptions released huge amounts of carbon dioxide and other gases into the atmosphere, causing global warming, acid rain, and ocean acidification.
As a result, about 75% of all species on Earth went extinct. Many early reptiles, large amphibians, and marine life forms disappeared. However, some groups—like dinosaurs, early mammals, pterosaurs, and crocodile relatives—managed to survive.
With many competitors gone, dinosaurs rapidly evolved and became the dominant animals on land, leading into the Jurassic Period, the heart of the Age of Dinosaurs.

The Jurassic

The Jurassic Period was the middle chapter of the Mesozoic Era, lasting from about 200 to 145 million years ago. It lasted 55 million years. It followed the mass extinction at the end of the Triassic and was a time of great growth, change, and dinosaur dominance.

During the Jurassic, the supercontinent Pangaea began to split into two large landmasses: Laurasia in the north and Gondwana in the south. This separation created new oceans and coastlines, leading to warmer, wetter climates with fewer deserts. Lush forests, swamps, and river valleys spread across the land, providing ideal conditions for large plant-eating dinosaurs.

The Jurassic Period came to an end around 145 million years ago, but unlike other geological periods, it did not end with a mass extinction. Instead, it faded gradually into the next era—the Cretaceous Period. During this time, the supercontinent Pangaea continued to break apart, creating new oceans and separating the continents into shapes more like what we see today. This caused changes in sea levels, climate, and habitats across the globe. While the overall climate remained warm, some areas became more seasonal and cooler. Although no sudden extinction occurred, the types of animals and plants on Earth slowly began to change. Some groups of large dinosaurs, like certain long-necked sauropods, started to decline in some regions. At the same time, new types of dinosaurs began to appear, including early forms of ceratopsians (horned dinosaurs) and hadrosaurs (duck-billed dinosaurs). One of the most important changes was the appearance of the first flowering plants (angiosperms) toward the very end of the Jurassic. These would go on to transform ecosystems in the Cretaceous.

The Cretaceous

The Cretaceous Period was the final period of the Mesozoic Era, lasting from about 145 to 66 million years ago. It followed the Jurassic Period and ended with one of the most famous events in Earth’s history—the mass extinction that wiped out the non-avian dinosaurs.

During the Cretaceous, the Earth looked very different. The supercontinents had broken apart, and the continents were slowly moving toward the positions they hold today. Shallow seas covered large areas of land, and the climate was warm and humid, with no ice at the poles.

This period saw a great explosion of life. Many well-known dinosaurs lived during the Cretaceous.
Flowering plants (angiosperms) first appeared and began to spread rapidly, changing plant life forever. These plants attracted insects and helped develop more complex ecosystems.
In the skies, pterosaurs still flew, but birds were becoming more common and advanced. In the oceans, large marine reptiles like mosasaurs and plesiosaurs ruled the waters, along with many types of fish and ancient relatives of modern sea animals.

In the Cretaceous Period, sauropods in North America were no longer the dominant group of herbivorous dinosaurs with the exception of Alamosaurus, with the ornithopod and ceratopsian dinosaurs, such as Edmontosaurus and Triceratops, becoming the most abundant (this being most evident by the Late Cretaceous epoch). However, on other landmasses such as South America and Africa (which were island continents much like modern Australia) sauropods, in particular the titanosaurs, continued to be the dominant herbivores.

The Cretaceous Period ended about 66 million years ago with one of the most dramatic and well-known events in Earth's history: a mass extinction that wiped out around 75% of all life on Earth, including all non-avian dinosaurs.
The most widely accepted cause of this extinction is a massive asteroid impact. The asteroid, about 10 kilometers wide, struck the Earth in what is now the Yucatán Peninsula in Mexico, creating the Chicxulub Crater. The impact caused enormous fires, earthquakes, and sent vast amounts of dust and debris into the atmosphere. This blocked sunlight, cooled the Earth, and disrupted the global climate for years.
In addition to the asteroid, intense volcanic activity in a region called the Deccan Traps (in present-day India) may have also contributed to the extinction. These eruptions released toxic gases and greenhouse gases, making Earth’s environment even more unstable.
All non-avian dinosaurs became extinct, large marine reptiles like mosasaurs and plesiosaurs disappeared, flying reptiles like pterosaurs vanished and many types of plants, insects, and ocean life also died out. However, some life forms did survive, including: birds (the only surviving dinosaurs), small mammals, which later evolved and thrived, some reptiles, amphibians, and marine species.