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Course: American Museum of Natural History > Unit 1
Lesson 1: What is a dinosaur?- What makes a dinosaur a dinosaur?
- What is and is not a dinosaur?
- What is and is not a dinosaur?
- How do dinosaurs get their names?
- How do dinosaurs get their names?
- Linking birds and dinosaurs
- How do we know which kinds of dinosaurs were most closely related?
- How do we know which kinds of dinosaurs were most closely related?
- Quiz: What is a dinosaur?
- Exploration Questions: What is a dinosaur?
- Answers to Exploration Questions: What is a dinosaur?
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What is and is not a dinosaur?
Scientifically, the group called dinosaurs includes all the animals that evolved from the very first dinosaur, the common ancestor. A key evolutionary innovation of dinosaurs is that they walk with a fully erect posture, holding their hind legs vertically under their hips. The top of the thighbone (or femur) has a knob or head that sticks out to the side of the rest of the bone and fits into the hip socket (or acetabulum) in the pelvis. The hip socket has a hole in the center, as well as a rim of bone along the upper margin, which helps support the weight of the body on the leg. Since these features are present in all known dinosaurs, we deduce that they first evolved in the common ancestor. Created by American Museum of Natural History.
Want to join the conversation?
"The top of the thighbone (or femur) has a knob or head that sticks out to the side of the rest of the bone and fits into the hip socket (or acetabulum) in the pelvis" isn't that the same in humans?(10 votes)
Yes. This is a case of 'convergent evolution', where two distantly related groups of animals evolve similar characteristics. Like how over time dolphins became as streamlined as any fish. In the case of dinosaurs and early mammals, they were solving the same problem - taking an earlier reptile hip and leg configuration and making it more efficient by getting the legs under the hip. Since they both had a similar starting point, it's not terribly surprising that the solutions look somewhat similar.(7 votes)
Why can't all ancient reptile be dinosaur? i know that dinosaur have some special bones but Dinosaur means terrible lizard and i am pretty sure that a giant ancient lizard is a terrible lizard(3 votes)
That's just what the name means, in reality there's tons of different biological differences between different groups of reptiles.(3 votes)
- Why do they still call it the "bird-hipped group" if birds are actually sauricians?(2 votes)
My guess is that when they named these groups, they didn't know which group modern-day birds would fall into. They were just trying to classify the dinosaurs into different groups: those that had hips like bird-like dinosaurs and those that had hips like the reptiles.(4 votes)
what color were dinosaurs?(1 vote)
Well we cant say what color dinosaurs were, because we don't have any evidence.(4 votes)
- How could the Trex walk and not fall over(1 vote)
- It had its tail to balance. And its written T. rex :P(3 votes)
At school when my teacher taught us about dinosaurs one of the kids in my class told everyone that one type of dinosaur that was able to fly never went extinct.
Is that true?(1 vote)- What's the difference between the ornithischia dinosaurs and the reptile dinosaurs?(1 vote)
- The Trex walks on its back legs therefore its related to birds(1 vote)
How do Scientists know that they're dinosaurs or not ?(1 vote)- Because of the various differences in their biology.(2 votes)
- I love science so my question is why birds descend from the reptiles if they don"t have scales feather and some with the wing span of a prehistoric bird so really the hole in the hip determines whether the bird is a descendant of the reptile side not the birds but the dinosaurs.(1 vote)
Certain, well most birds have scale under the skin the feathers connect to really mini ones. These usually live in Africa(1 vote)
what year did we find dinosaurs?(1 vote)
Video transcript
Dinosaurs are a group of reptiles that is
composed of two great subcategories. One is that
the Bird-hipped dinosaurs or the ornithischians and the other is the reptile-hipped dinosaurs, or saurischians. So basically dinosaurs are all the
animals that are descended from the last common
ancestor of those two groups, the saurischians and the ornithischians. An interesting fact is that birds, which are a kind of dinosaur are saurischians so that they're in the
reptile-hipped group of dinosaurs not in the bird-hipped group.