Many different kinds of dinosaurs lived and became extinct during the age of the dinosaurs. Fossils are all that is left of them. To be the first living thing to set eyes on something that has been burried for over 100 million years is exciting.
Below are several periods of time that the dinosaurs ruled. Click on the button to go to each period of interest. The dinosaur family tree shows a timeline of the different dinosaurs in different periods.
The Earth was very different in the Triassic Era. About 20 million years before dinosaurs, over 90% of all plant and animal species then alive on land and sea died out. In the Early Triassic there were very few species alive. All the continents were connected so all animal and plant species of this time were very simular. This was a time before grass and flowering plants, which includes most trees and shrubs today. The "trees" were drab ferns and podocarps. The low ground cover was ferns and mosses. The continent was called Pangaea and the central region was a vast desert.
Dinosaurs appeard at this time and also flying reptiles, various kinds of marine reptiles, crocodiles, turtles and the earliest true mammals. Toward the end of the Triassic there was another extinction which wiped out many of the non-dinosaurs. It was then that the dinosaurs really began to multiply and diversify.
The earliest dinosaurs were pretty small. The plant-eaters started to become larger. Sauropods had huge elephant-like bodies and long necks and tails. The dinosaurs in this era were found in the Morrison Formation. The Morrison Formation was deposited approximately 155-145 million years ago and covers a large area of the western US. The environment was diverse, ranging from arid deserts to flood plains and swamps. Fossil plants suggest a wetter invironment than the rock record and this may mean that the climate was seasonal.
In the Early Jurassic period the herbivores and carnivores both increased in size. The sauropods grew staggeringly large, the carnivores got larger too but not as large as the herbivores.
There are two main types of dinosaurs, named from the configuration of their pelvic bones; bird-hipped and lizard-hipped. Sauropods and theropods are lizard-hipped; Stegosaurus is a bird-hipped dinosaur.
While huge dinosaurs dominated the land there were also large marine reptiles ruling the seas. There was the Ichthyosaurs, fish reptiles, with limbs modified into flippers, dorsal fins, and vertical tail flukes. The Plesiosaurs became numerous too. There were two kinds of plesiosaurs--the large short-necked pliosaurs which were the top predators of the seas and the long-necked plesiosaurs which probably fed on small fish and other small prey.
When marine reptiles are first found in the fossil record they are already specilized and it is difficult to trace their ancestry. There is little idea from which groups of land reptiles the Ichthyosaurs and plesiosaurs were decended.
Other reptilians of the middle-late Jurassic seas were the marine crocodiles. There were a couple different types of marine crocodiles, one of which was so adapted to life in the seas that their limbs had turned into flippers and they even had a fluke on their tails.
The Late Jurassic animals are bassed mainly on fossil finds from the Oxford Clay. The Oxford Clay was deposited in the shallow marine environment when the British Isles and part of Western Europe was on archipelago.
This was a period of great change, new types of dinosaurs were appearing and flowering plants made their debut. The dinosaurs would be more abundant and larger and the flowering plants would become the most common plants on Earth. There was still no grasses, though.
Ornithopods are herbivores, more plentiful and smaller than sauropods. The difference between them was that Ornithopods could chew their food, therefore needing smaller bodies . The Sauropods needed larger bodies so their guts could break down the food over several days. Bird-like dinosaurs called theropods, popularly known as raptors, also appeared. their arms were fairly long and more bird-like pelvis. The earliest known bird--Archaeopteryx-- comes from Germany. Most of these early birds look very primitive and some still have teeth. The largest animals to fly were pterosaurs. They seem, to our eyes, to be a mixture of bird and bat. Their long beaks remind us of birds, but they had membraneous wings.
At the end of the Cretaceous Period, all the dinosaurs died out. There have been many ideas put forth as an explanation for this; two that are most likelly. The gradualist theory and the impact theory. The gradualist theory is that the extinction was due to climate change. The impact theory suggests that a meteorite hit the earth and triggered a nuclear winter. In addition at the end of the Cretaceous there were a lot of volcanic eruptions.