The following questions were answered by dinosaur expert Don Lessem and paleontologist Tim Rowe .

Q: How did the first dinosaur get on Earth?

A: Dinosaurs evolved from more primitive reptiles about 230 million years ago. Among the earliest-known dinosaurs was eoraptor from Argentina, a dog-sized meat-eater, 228 million years old. (Don Lessem)

Q: Why weren't people alive when dinosaurs lived?

A: People evolved from earlier mouse-sized mammals that were around all through dinosaur time, but didn't get any bigger than a house cat. Only after the dinosaurs disappeared — 65 million years ago — did mammals get larger and more varied. Eventually, the primate mammals — the ape family — emerged and led to one very smart ape about one million years ago — us. (Don Lessem)

Q: How did the first dinosaur come to life?

A: Dinosaurs got here by evolving through a series of changes from more primitive reptiles. Nobody can really say why any animal evolves. It's a matter of chance and survival of the strongest. If you start life all over again, or get rid of an animal, it can never come back. So no more dinosaurs — except in Jurassic Park. (Don Lessem)

Q: Are animals of today related to dinosaurs? If yes, which ones?

A: Birds are the direct descendants of meat-eating dinosaurs in most scientists'opinions. Living reptiles like crocodiles are relatives of dinosaurs, but they came from animals that developed before dinosaurs, so they are just cousins of dinosaurs. Dinosaurs aren't birds or reptiles. They're dinosaurs, a separate, special group. Some living animals, like reptiles, look a lot like what we imagine dinosaurs to be, but that's just a coincidence. Reptiles all have bent legs, and dinosaurs have straighter legs. Dinosaurs walked with their legs underneath them — that's one way to tell a dinosaur is a dinosaur. (Don Lessem)

Q: There is a theory of dinosaur extinction that dinosaurs did not "die out" but evolved into reptiles and birds of today. What do you think of that one?

A: Many scientists think birds are dinosaurs. Certainly, it appears that birds are descended from meat-eating dinosaurs and the earliest birds look just the same, except for feather impressions, as small meat-eating dinosaurs. It's a question of semantics then whether birds are living dinosaurs or their closest living relatives. What we call reptiles were around before, during, and after dinosaurs. Dinosaurs evolved from more primitive reptilian relatives but belong to their own separate group. (Don Lessem)

Q: Do you think that some of the smallest dinosaurs could have evolved into birds?

A: Little dinosaur meat-eaters were probably the ancestors of birds, but we aren't sure which ones. (Don Lessem)

Q: Are any modern-day pets related to dinosaurs?

A: There is a lot of recent research that suggests birds are the closest living relatives of dinosaurs — in fact many paleontologists are now saying that birds are living dinosaurs. So your pet parrot has a very distinguished history! I keep chickens and a turkey as pets at home, and the resemblance to extinct dinosaurs is really striking, especially when you look at their feet (the feathers hide a lot of other resemblances besides the feet). (Tim Rowe)

Q: In what ways were some dinosaurs like birds?

A: Dinosaurs were like birds in having hollow bones, but so did pterosaurs. Dinosaurs walked upright as birds do and meat-eating dinosaurs have very similar skulls to birds. Some of the smaller dinosaur meat-eaters have bodies and arms similar to birds'as well. The first bird, archaeopteryx, looks nearly identical to the small meat-eating dinosaur of the same time, compsognathus, except it has feathers. (Don Lessem)

Q: What fish did dinosaurs evolve from? How did birds evolve?

A: Fish aren't closely related to dinosaurs, but birds are. Birds are descended from meat-eating dinosaurs. (Don Lessem)

Q: How were some dinosaurs able to evolve into warm-blooded animals?

A: Some dinosaurs may have been warm-blooded or at least partially so. The descendants of meat-eating dinosaurs are warm-blooded — they're birds. So dinosaurs were probably on the way to warm-bloodedness themselves. (Don Lessem)

Q: How are reptiles and amphibians different and related?

A: Reptiles evolved from amphibians long before dinosaurs, about 300 million years ago. Reptiles had a better breathing system than amphibians before them. Instead of a throat pump they moved their rib cage like we do, so the size of their lungs, not their mouth, determined how much air they could take in. Reptiles also had a horny layer on their scales and armor, unlike amphibians, so they could live all their lives on land. (Don Lessem)

Q: Why did some dinosaurs have long tails?

A: We don't know why dinosaurs had long tails but it was probably to keep them from falling on their faces, since they had a lot of weight in the front of their body leaning forward over their hips. (Don Lessem)

Q: What animal did the ichthyosaurus evolve from?

A: Ichthyosaurs were related to other marine reptiles and have no living descendants. They were related to early reptiles on land that returned to the sea more than 230 million years ago. We don't know which reptiles though. (Don Lessem)

Q: What were some characteristics of the mammal-like reptile?

A: Mammal-like reptiles lived before and in the early part of dinosaur time. They were the ancestors of mammals, though they looked like reptiles. However, their skulls had a pair of openings under each eye, unlike any other reptiles, and like mammals. (Don Lessem)

Q: Was there a specific amphibian that reptiles evolved from?

A: We don't have enough fossils to know. And it's always hard to find the closest relative. How would we know there isn't one nearer to reptiles that we haven't found yet?

(Don Lessem)