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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?
The group called dinosaurs includes all the animals that evolved from the very first dinosaur, the common ancestor. Because the fossil record is incomplete, we have not found fossils of this common ancestor; however, based on the characteristics we see in all dinosaurs, we can determine new and unique characteristics it possessed.
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.
In popular culture, many other kinds of animals, which don't have this fully developed hip and leg structure, are often incorrectly called dinosaurs. Some examples include Mesozoic marine reptiles, such as plesiosaurs, mosasaurs and ichthyosaurs, as well as a group of Mesozoic flying reptiles called pterosaurs.
Want to join the conversation?
- What would be the correct overarching/all-encompassing term to refer to 'real' (hole-in-hip) dinosaurs and the (plesio/mosa/ichtyo/ptero/etc.) 'saurus'-reptiles that lived during Age of the Dinosaurs?(20 votes)
- If you want the term than includes the reptile ancestors of mammals, which includes dimetrodon and some other ancient reptiles with 'saurus' (which just means 'lizard') in the name, then you have to go one step up from diapsids to amniotes, the group of reptiles with eggs suited for laying on land. Amniotes includes the diapsids and the synapsids.(10 votes)
- How similar is hip joint anatomy of dinosaurs and humans ? Is there any evolutionary advantage for brain development by having erect posture?(7 votes)
- Now there's a question! Maybe, and there's a lot of debate about this, but early human relatives were walking upright for a very long time before their brains became significantly larger. Also, most mammals have erect posture in the same sense as dinosaurs, with their legs tucked under their bodies. Humans just happen to do it on two legs.(7 votes)
- So if pterosaurs aren't dinosaurs, does that mean pteranadons aren't dinosaurs? What species are pteranadons anyway?(4 votes)
- Pteranodon is a species of pterosaur, so no its not a dinosaur. Also when you say a dinosaur's (or any scientific animal name) name, its said the same even if its plural. So its Pteranodon always, never Pteranodons(4 votes)
- how many species of dinosaurs are there?(5 votes)
- At least thousands. See the wikipedia article on the matter here: https://en.wikipedia.org/wiki/List_of_dinosaur_genera. New species are being discovered every year and as our understanding grows, how we classify dinosaurs changes.(1 vote)
- Are there dinosaurs living?(3 votes)
- Yeah... Remember, birds are the descendants of dinosaurs.(3 votes)
- I like this it helps me with what i need to know about dinosaurs they are so cool(2 votes)
- Please put this in tips and thanks I think 😸(2 votes)
- are dino saurs related to crocodiles(2 votes)
- well except for the microcania (megafauna) no liing ancestor(2 votes)
- what made the dinosaurs extinct(2 votes)
- No one exactly knows. It was either a massive volcano eruption, or a giant meteoroid from outer space. Many evidence shows that it was a giant asteroid like the huge crater in Mexico.(1 vote)
- how tall is the tallest dinosaur(2 votes)
- Not all Dinosaurs are reptiles,Theropods and Soaropodamorphs(Sauropods and Prosauropods)are closer related to Avilens(birds).(2 votes)