Origin and Evolution of Dinosaurs
Origin and Evolution of Dinosaurs Dinosaurs ruled the earth for millions of years until they mysteriously disappeared about 65 million years ago. Just like there is no definite theory that explains the mass extinction of dinosaurs, for a long time, scientists did not have a definite answer to the question, when did the dinosaurs originate. But, thanks to the discoveries of dinosaur fossils from around the world, we now know quite a lot about their origin an evolution.
The early dinosaurs evolved from the archosaurs in the latter part of Triassic period known as the Ladinian age, about 230 million years ago. The fossil remains found on rock formations at this period suggest that the early dinosaur was a small bipedal predator. Fossil remains of another dinosaur dating back to 235 million years ago in Argentina bears similar physical characteristics to this early dinosaur.
The dinosaurs appeared in the latter part of the Triassic period and flourished through the Jurassic period finally becoming extinct in the late Cretaceous period.
Although dinosaurs evolved from archosuars, there are definite characteristics that make them different from their ancestors. These characteristics can be found on all dinosaurs from the primitive forms in the Triassic to the most advanced ones in the late Cretaceous. The dinosaurs, unlike their ancestors were able to stand upright due to the changes in their hind limbs. It also helped them improve in their locomotive abilities. Coupled with higher metabolism this evolutionary development was the main reason for their success as a species.
Evolution and classification of Dinosaurs
Dinosaurs can be divided in to two major groups, Saurischians and the Ornithischians, with subgroups evolving from them.
1) Ornithischians
The ornithischians include a series of plant eating dinosaurs such as the armoured stegosaurs and ankylosaur, the horned and dome-headed dinosaurs and the duckbills. The ornithischians are the main dinosaurs group that include all different types of dinosaurs that does not belong to the Saurischians. The ornithischian dinosaurs appears in all the three major periods in the Dinosaur history.
2) Saurischians
The Saurischians comprises of both the meat-eating theropods and the plant-eating sauropodomorphs. They developed through the Jurassic period and ended in the Cretaceous period.
• Types of Ornithischians
The earliest known dinosaur belonging to this group is the 228-million-year-old small Pisanosaurus, whose fossil was found in Argentina. Since the Pisanosaurus walked on two limbs and ate plants, it would be safe to assume that its ancestors were also a bipedal herbivore.
• The armored ones- These include hyreophorans-the group that includes the stegosaurs and Ankylosaurus. They have a distinctive feature of armor comprising bony scutes and plates that covered most of the entire surface of the body. They appear from Late Jurassic through late Cretaceous times.
• Dome headed and horned (marginocephalians)- These dinosaurs have a bony shield that projects from the skull. One of the most known dinosaurs of this group is the Triceratops which has three horns.
• Ornithopods- These dinosaurs have special dental batteries that helped them in grinding plant matter. Appearing in late Jurassic period they continued till the end of the cretaceous. This group also includes the duckbilled dinosaurs which flourished during the late cretaceous period.
• Types of Suarischians
• Sauropodomorphs- This group includes the small headed and long armed prosauropods and the massive, long necked sauropods, the largest land animal of all time. These dinosaurs can be traced back to Triassic period and by the Jurassic period they evolved into sub groups. Plateosaurus is a well-known dinosaur of this group.
• Theropods – Theropods fall in to several subgroups; prominent among them are ceratosaurs and the tetanurans. The major dinosaurs in this group are sail-backed Spinosaurus of Egypt, long-snouted Baryonyx of England and Niger, Allosaurus from the Late Jurassic of North America, Carcharodontosaurus and Giganotosaurus, from the Late Cretaceous of Africa and South America. There are others like Oviraptor, which is a birdlike dinosaur and hunters like Velociraptor.
The Evolution of Dinosaurs in to Birds
The dinosaurs, from their early days as small bipedal, herbivore went through many major evolutionary changes in the millions of years of its existence that include the development of feathers. Originated as cold blooded animals, the feathers helped them become warm blooded and airborne, thus finally evolving into birds.