PREHISTORIC LIFE
APRIL 5, 2021
A short story of the first dinosaurs on earth
The first dinosaurs lived around 250 million years ago during the Mesozoic era. They first appeared during the Triassic period and ruled the Earth about 175 million years.
An extinction event happened 65.5 million years ago and wiped out all of them except for the avian dinosaurs. No exact cause of their extinction so far, but most scientists believe it was likely because of giant asteroid impact and extreme climate change plus many different factors. Modern taxonomy classifies all dinosaurs as reptiles and not birds or mammals. This is because most of the characteristics of dinosaurs are found in reptiles than in the birds or mammals.
In the 19th century, Dinosaurs fossils were first recognized. The term dinosaurs was used by the paleontologist, Richard Owen in 1842. Taken from the Greek deinos, meaning “terrible” or “fearfully great” and sauros for “lizard” or “reptile”.
One of the carnivorous dinosaurs was Megalosaurus or “Great Lizard”. The name was officially granted by the British Naturalist, William Buckland in 1824. Compared to its front limbs, Megalosaurus hind limbs were much stronger. This made the animal to rise up on to its hind limbs when it was running after its prey and would then tear great chunks of meat from the body which it swallowed whole. This fierce beast theropod dinosaurs lived during the Middle Jurassic period, abiut 166 million years ago.
With dangerous enemies like Megalosaurus lying in wait for them, it is not surprising that some of the plant-eating dinosaurs called thyreophorans developed an armor of bone to protect themselves. Thyreophorans meaning “shield bearers” and they were the first armored dinosaurs.
One of them was Scelidosaurus, which had many lumps of bone in its skin, rather as crocodiles have today. They lived during the Early Jurassic period around 191 million years ago. This dinosaurs developed strong bony plates called scutes in their skin that gave them protection against fierce, hungry predators. Because Scelidosaurus was one of the first dinosaurs to be found as a complete skeleton, scientists are able to examine its anatomy to gain better knowledge.
Another herbivores dinosaur was Stegosaurus, from Greek stegos meaning roof and sauros meaning lizard. They lived about 155 and 150 million years ago during the Late Jurassic period. Stegosaurus is the most popular dinosaur from a group known as Stegosauria, and it had 17 triangular plates of bone all along its back.
The largest plate were around 60 cm (2 ft) tall and 60 cm (2 ft) wide. Some expert says those armor plates were used for mating while others believe they were used to protect from predators like Allosaurus and Ceratosaurus. Furthermore, Stegosaurus was also able to defend itself using its tail, on which were several long, sharp, bony spikes that reached around 50 cm (2 feet) to 90 cm (3 feet) in length.
In order to clone a dinosaur, like in the movie “Jurassic Park”, we would need the DNA but there is no surviving dinosaurs DNA so far.
The biggest of all the dinosaurs were the enormous herbivore called sauropods. These largest animals to have ever lived on land such as Brontosaurus, Brachiosaurus, Diplodocus and Apatosaurus. Their size could grow the length of three school buses and were so heavy. They lived mostly during the Jurassic and Triasic period and existed until the late Cretaceous period until the great extinction occured.
The young sauropods were often eaten by carnivore such as Megalosaurus. The adults were probably too big and too strong for the carnivores to attack. Like all plant-eater animals, they had big bulky bodies to contain the masses of plant food as it was slowly digested.
Sauropods had long, thin necks like giraffes. Many assume that they probably used their long necks to eat some leaves of the higher branches of trees, which smaller animals could not reach. However this assumption can not be entirely true because of some biological limitation of this animal such as their hearts.
The biggest sauropods was Argentinosaurus, discovered in Argentina and named after the location. They were roaming in what is now South America nearly 100 million years ago. It is estimated this animal weighted between 65-98 tons in weight and was around 30 – 35 meters (98 – 118 feet) in length, about 10 times bigger than the biggest elephant.
Another big size dinosaurs of sauropods family is Brachiousaurus. They developed longer front limbs than the other sauropods. Its height was about 12 – 16 meters (40 – 50 feet) tall above the ground and they lived in North America during the Middle and Late Jurassic period, around 154 – 153 million years ago.
Regarding their living place, Paleontologists used to assume for many years that giant sauropods spent most of their time in lakes and swamps, using their long necks to keep their heads above the water. But it seems that some subgroups of sauropods preferred to inhabit coastal environments. Today, it is believed that the sauropods lived on land, meaning that they were fully terrestrial animal.
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