Dinosaurs! - What is a dinosaur?

INTRODUCTION TO DINOSAURS
What is a Dinosaur? The word dinosaur means "terrible lizard". Dinosaurs encompass the reptiles that, for 165 million years, dominated the earth's land and became extinct 65 million years ago. To put that into perspective, the first human ancestors were thought to have appeared about 2-3 million years ago. Dinosaur Diversity All dinosaurs belonged to one of two orders - Saurischia, (lizard-hipped) and Ornithischia, (bird-hipped), which can be differentiated by the anatomical variations in the structure of their hips. Both Saurischian and Ornithischian dinosaurs likely evolved from the same distant ancestor. Below is a diagram showing the skeletal differences between Saurischian and Ornithischian dinosaurs. Saurischians Saurischian dinosaurs encompassed 2 suborders: theropods and sauropodomorphs. Theropods include large, 2-legged meat-eaters like Albertosaurus. Sauropodomorphs include large quadropedal plant-eating dinosaurs such as Diplodocus and Ultrasaurus. Ornithischians Ornithischian dinosaurs were all plant-eaters. This order included 3 suborders which were: ornothopods (the duck-billed dinosaurs), thyreophora such as ankylosaurus and stegosaurs, and lastly the suborder marginocephalians which included dinosaurs such as triceratops and pachycephalosaurus.	When dinosaurs evolved an upright 2-legged posture, they had to evolve a new attachment site for the muscles that swung the powerful hindlimbs forward. Lizard-hipped dinosaurs evolved a downward and forward extension of the pubis-bone to which the muscles attached. In bird-hipped dinosaurs the muscles were attached to either a forward extension of the illium or in later types to a new "pre-pubis" extension of the pubis.

INTRODUCTION TO DINOSAURS

What is a Dinosaur?

The word dinosaur means "terrible lizard". Dinosaurs encompass the reptiles that, for 165 million years, dominated the earth's land and became extinct 65 million years ago. To put that into perspective, the first human ancestors were thought to have appeared about 2-3 million years ago.

Dinosaur Diversity

All dinosaurs belonged to one of two orders - Saurischia, (lizard-hipped) and Ornithischia, (bird-hipped), which can be differentiated by the anatomical variations in the structure of their hips.

Both Saurischian and Ornithischian dinosaurs likely evolved from the same distant ancestor.

Below is a diagram showing the skeletal differences between Saurischian and Ornithischian dinosaurs.

Saurischians

Saurischian dinosaurs encompassed 2 suborders: theropods and sauropodomorphs. Theropods include large, 2-legged meat-eaters like Albertosaurus. Sauropodomorphs include large quadropedal plant-eating dinosaurs such as Diplodocus and Ultrasaurus.

Ornithischians

Ornithischian dinosaurs were all plant-eaters. This order included 3 suborders which were: ornothopods (the duck-billed dinosaurs), thyreophora such as ankylosaurus and stegosaurs, and lastly the suborder marginocephalians which included dinosaurs such as triceratops and pachycephalosaurus.

When dinosaurs evolved an upright 2-legged posture, they had to evolve a new attachment site for the muscles that swung the powerful hindlimbs forward. Lizard-hipped dinosaurs evolved a downward and forward extension of the pubis-bone to which the muscles attached. In bird-hipped dinosaurs the muscles were attached to either a forward extension of the illium or in later types to a new "pre-pubis" extension of the pubis.

How we know what we know about dinosaurs

Thanks to advances in the field of paleontology, some exciting new fossil-finds, and some very dedicated and professional paleontologists, paleobotanists and geologists (among others), we are learning new things all the time about dinosaurs.

The biggest evidence we have that tells us about dinosaurs are their fossilized bones. From these fossilized skeletal remains, we can tell alot about the dinosaur it belonged to; size, shape, feeding habits etc. The only thing that is left solely to our imagination is the dinosaur's colour!

Also, there is an abundance of dinosaur "trackways" (footprints), that have been discovered in this century which have given us a greater understanding of dinosaur lifestyle, gait and speed.

One of the most important finds have been dinosaur eggs with embryos still intact, albeit fossilized. These eggs, sometimes found still within the nest, have led most Paleontologists to surmise that some dinosaur species were caring, nuturing parents that raised their young until they were able to fend for themselves.

These new finds have given us a totally different perspective of the dinosaurs. No longer are they thought of as dim-witted behemoths of the long-ago past, but are now known to have been agile, complex and even nuturing creatures that mightily ruled their world for 165 million years.
The Earth of the Dinosaur

During the 165 million years that the dinosaurs were dominant on the earth, the face of this planet was undergoing considerable changes. Continents were moving and climates were changing.

	This is what the earth looked like during the Mid-Triassic era. The super- continent was known as "Pangaea".
	Earth during the late Jurassic. South America and Africa are still attached but have broken off from North America and Eurasia. India is drifting towards Eurasia.
	By the late Cretaceous there were 2 landmasses in the northern hemisphere. "Asiamerica" was made up of Asia and Western North America. "Euramerica" comprised Europe and Eastern North America. Africa is almost in it's present position. Australia has still not separated from Antarctica.

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Page last updated: 9:57 AM 10/18/00