Dinosaurs were a group of reptiles that first appeared some 243 to 233 million years ago. During the time they existed, they were divided into two groups: avian (those capable of flight) and non-avian (those who are not capable of flight). The word “dinosaur” first came into existence in 1841 after Sir Richard Owen, a paleontologist, used it to describe some fossil remains.
It is generally accepted that non-avian dinosaurs became extinct around 66 million years ago, most likely as a result of a meteor's impact on Earth. However, scientists still to this day disagree on whether or not the meteor had an instant or residual impact, the latter as a result of changed climate and overall living conditions.
Origins of Dinosaurs
Dinosaurs emerged during the middle to the later stages of the Triassic period, which was between 201 and 251 years ago. This emergence was just after the Permian–Triassic extinction, which was some 250 million years ago and destroyed around 95% of the life that was present on earth. The data on the first dinosaurs is scarce although some theories state that dinosaurs were tiny animals at first, which would help to explain why they were not dominant during their appearance. The dominant species that were not wiped out during the Permian–Triassic extinction were wiped out during the Triassic–Jurassic extinction event, which was around 200 million years ago. Eventually, after years of evolution and changes, dinosaurs went on to become the apex predators of their world until their extinction.
The Impact Event
One of the most widely accepted theories about the impact event appeared in 1980 from Walter Alvarez and his team. Alvarez argued that the impact event was most likely an asteroid that hit some 66 million years ago, which would coincide with the time of the extinction event. Despite the evidence to support this theory, scientists are unclear whether the asteroid was the cause of the extinction or it accelerated the process. In fact, even Alvarez, who passed away in 1988, agreed that other factors such as a drop in the level of the sea and the Indian Deccan Traps might have also played a part in the extinction.