What is the Pangaea?

About 200 million years ago, all the continents on Earth were actually one huge “supercontinent” surrounded by one enormous ocean. This gigantic continent, called Pangaea, slowly broke apart and spread out to form the continents we know today.

When and how did dinosaurs appear?

Around 251 million years ago, at the end of the Permian period, a mass extinction wiped out most of life on Earth. In its wake arose a group of egg-laying reptile precursors called archosaurs, the common ancestors of dinosaurs, flying reptiles known as pterosaurs, and crocodiles. At some point during the next period, the Triassic, pterosaurs and dinosaurs split off from the crocodile lineage. What early dinosaurs and their closest relatives looked like still remains somehow a mystery, because few fossils exist from the dawn of the dinosaurs. However, as today, the archosaurus seems to be the closest we can get to the appearance of dinosaurs on Earth.

Since the fossil record for dinosaurs is incomplete, we do not have fossils from the very first dinosaur that ever lived. Based on the age of the specimens that we do have, that first dinosaur may well have lived in the early Triassic Period. The earliest dinosaurs for which we do have well-documented fossils are found in Late Triassic Ischigualasto Formation in northern Argentina. Skeletons discovered in these rock layers include the meat-eating dinosaurs Herrerasaurus and Eoraptor, as well as the plant-eating dinosaur Pisanosaurus.

Reference: American Museum of National History

Types of dinosaurs:

Historically, dinosaurs have been divided into two main groups: saurischians (“lizard-hipped”) and ornithischians (“bird-hipped”), classified by their hip structure. In saurischians, the two lower bones of the hip point away from each other, as in lizards; and in ornithischians, the two lower hip bones both point backwards, as in birds. Ironically, birds by ancestry are saurischians rather than ornithischians (their evolution of true “bird hips” occurred after the saurischian–ornithischian split). The saurischians are divided into theropods and sauropodomorphs. Theropods are the classic bipedal carnivorous dinosaurs, from Coelophysis to Tyrannosaurus, and also include birds. Sauropodomorphs include the enormous quadrupedal, herbivorous long-necked, long-tailed sauropods (Brachiosaurus, Diplodocus) and their cousins the “prosauropods”. Finally, the ornithischians are harder to define because they include several very different groups, but all ornithischians share a special “beak bone” (the predentary) at the tip of the lower jaw.

More about this topic at https://www.nps.gov/subjects/fossils/major-groups-of-dinosaurs

How did dinosaurs become extinct?

Today, paleontologists have discerned that most dinosaur lineages disappeared by about 66 million years ago after intense volcanic activity, climate change and a catastrophic asteroid impact triggered one of the worst mass extinctions in our planet’s history.

The Natural History Museum has a very good article about this phenomena.

How were dinosaur fossils formed?

Most living things decompose relatively quickly after death. However, if soon after they die, the remains get covered in sediment such as mud, sand, and even lava or volcanic ash. Over time layers of sediment build over the top and hardens into rock. At the same time this happens, water seeps into the sediments and bones. It leaves behind minerals, turning the bones to stones and creating a fossil. Around 99% of the fossils we find are from marine animals, such as shellfish and sharks. As they lived in the sea, mud or sand could bury them very quickly after their death. Most dinosaur fossils we have found belong to animals that were living near to a lake or a river which facilitated the remains to get covered in mud and silt. There are other events that can help fossils form, like animals that get buried when still alive by mud (rare cases) or volcanoes’ eruptions. Dinosaur can also leave behind footprints, and impressions of skin and feathers. We learn about dinosaurs through fossils, these discoveries are very important to understand the history behind us.

More on this at National History Museum