When did the Dinosaurs Live on Earth?
If we could work backwards from the animals left to us in the world today, we would find that the story of life on Earth stretches back more than four thousand million years into the past - a span of time which is quite impossible for us to comprehend.
The first life probably began in the seas around 4500 million years ago, then, millions of years later the first creatures crawled out of the water and started to live on the land. It was not until about 500 million years ago that the first animals with backbones (vertebrates) evolved.
During those vast periods of time countless species have evolved, multiplied, declined and vanished forever. Some of the more successful species actually 'dominated' the world for a few million years before they too declined and disappeared.
Today, humans are the dominating species - and yet we have only held this position for a few thousand years.
Reptiles dominated life on land during the Mesozoic era, a period of time which extended from approximately 225 million to 65 million years ago.
The Age of Reptiles lasted for nearly 200 million years - and then ended comparatively suddenly. As yet, we do not know exactly what killed off the great dinosaurs - but almost certainly it was a sudden and quite catastrophic change in the earth's climate which occurred towards the end of the Cretaceous Period about 65 million years ago.
Perhaps it will be possible one day to discover just what did happen to end the reign of the reptiles after 200 million years as dominating animals. We constantly unearth fossil remains which provide us with more and more information about the animal species of those far off times, so we may yet find the answer to the question that has never been properly answered.
Image: Dinosaurs by Norman Z
What are Dinosaurs? Sam Rae and Lisa Hendry for The Natural History Museum, available here: https://www.nhm.ac.uk/discover/what-are-dinosaurs.html [Accessed 19/11/20]
These Are The Dinosaurs That Didn't Die, Victoria Jaggard, (May 2018) For National Geographic. Available here: https://www.nationalgeographic.com/magazine/2018/05/dinosaurs-survivors-birds-fossils/ [Accessed 19/11/20]
What Made a Dinosaur a Dinosaur?
Many prehistoric reptiles are referred to as 'dinosaurs' by mistake.
Dinosaurs were a type of reptile known as archosaurs ('ruling reptiles') which included the dinosaurs and the flying reptiles, pterosaurs.
Dinosaurs had a special stance, or way of walking. Their back legs were positioned underneath (perpendicular to) their bodies, instead of sprawling out at the sides, like other reptiles. This gave the an upright stance and allowed them to use far less energy to move than other reptiles (such as crocodiles).
Photo: Fred the Oyster
The dinosaurs ('terrible reptiles') were divided into two main orders, the Saurischia of which some were herbivores and others carnivores, and the Ornithischia which, as far as we know, were all herbivores. The chief difference in structure between the two kinds of dinosaurs was in the pelvis. Saurischians are often referred to as 'lizard-hipped' reptiles and the Ornithischians as 'bird-hipped'.
Dinosaurs also had two holes behind their eye sockets. They had strong jaw muscles that went through the holes to attach directly to the top of their skull. This meant that their jaws were able to open very wide and could bite down with extra force.
Dinosaurs lived on land, not in the sea. Marine reptiles, such as ichthyosaurs, plesiosaurs and mosasaurs are not dinosaurs.
Birds: The Modern Dinosaurs
Most people are familiar with the story of the asteroid which killed off the majority of the dinosaurs when it hit the earth in the late Cretaceous period. However, not all of the dinosaurs were wiped out and, through millions of years of evolution, they have been transformed: into the birds that we see all around the world today.
Archaeopteryx, a 150-million-year-old animal, is the oldest known link between dinosaurs and the birds we know nowadays. Although it had a mouth full of sharp teeth, it also had feathers on its wings and a wishbone that would be familiar to anyone who has ever eaten a roast chicken! In 1996 scientists discovered the first known fossil of a feathered dinosaur unrelated to birds, Sinosauropteryx prima, which was found to date back 130 million years. In 2005, bones from Antarctica were found that were dated to before the asteroid is known to have hit Earth. These fossilised remains of the Vegavis iaai can be dated back to around 67 million years ago and they look strikingly similar to those of modern day ducks and geese.
“There is no doubt that birds are dinosaurs,” says Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. “The evidence is so overwhelming, I would put it next to whether you’re going to question if humans are primates.”