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

Q: How do scientists know if they've found a dinosaur bone?

A: You can tell what you find is a dinosaur if you recognize the shape of the bone or tooth from other finds. Dinosaur bones are often larger than other animal bones, but not always. Often fragments are too small or broken up to be sure. Meat-eaters had bones that were hollow, but thicker usually than those of birds or pterosaurs. (Don Lessem)

We can identify the bones as those of a dinosaur because of their size and certain characteristics. Bones of other animals from the Jurassic are smaller and they look different, particularly the skull and the pelvis. (Bill Hammer)

Q: How can you tell which bone belongs to which dinosaur?

A: Well, it's not always easy. Sometimes the bones are scattered over a large area or mixed with other dinosaurs. Sometimes you can tell by comparing the individual one that was already described and maybe drawn by a scientist before. Or else it looks enough like one kind of dinosaur's distinctive bones, like the grinding teeth of a duckbill, to be certain it comes from that kind of dinosaur. Other times it's a mystery. Then maybe it is reason to name a new dinosaur from what you found. (Don Lessem)

Q: How do you know what to pick as a fossil and what to leave on the ground?

A: When we are out prospecting for bones, we first look at modern bones to give us a "search image" with which to look at the ground and to recognize fossil bone when we see it. Still, I pick up a lot of stuff that turns out to be just rock when I look at it under a magnifying glass or hand lens. All that stuff goes back on the ground, and I keep walking until I pick up something that really looks like bone when I look at it more closely. Shape, color, and texture all help in recognizing fossil bone. (Tim Rowe)

Q: How do scientists know how dinosaur bones should be put back together?

A: Putting bones together isn't too hard if you have a complete skeleton to compare it to. Otherwise it can be tough. Usually the shape of the bone tells you what body part it is. Mostly scientists don't put dinosaurs back together. It's too expensive, the bones are too valuable for studying, and you rarely get a complete skeleton anyway. (Don Lessem)

Q: How do they know exactly how to put the dinosaurs together?

A: The fact that dinosaur skeletons look so much like the skeletons of birds is one of the things that makes it possible for us to put their skeletons together properly. We also occasionally find complete skeletons, with every bone in place, so there is not much doubt how most of the skeletons go together. Most skeletons have several hundred individual bones. When the first ones were discovered, scientists were not sure how they went back together until they discovered the resemblance to birds. (Tim Rowe)

Q: When there's a pile of bones, how can you tell if they belong to several different dinosaurs?

A: Sometimes if the bones are pretty badly broken up it's hard to tell what animal they belonged to. But interspecific bone beds happen a lot — that means the bones of several species have been washed together. Usually you can tell pretty well what kind of dinosaur made them, at least to the level of what family or group of species. For instance, the little serrated teeth would belong to small meat-eaters and the big flat rib bones would belong to large plant-eaters. But you need a bone that is diagnostic, which means you can tell by its shape alone what animal uniquely had it, to be able to figure what animal produced the fossil. (Don Lessem)

Q: How do you know in which period certain dinosaurs lived?

A: Usually you can tell the time when the dinosaur lived by the age of the rock it is in. You tell the rock's age by small fossils of plants and little animals that we already know the age of, or by chemical testing if it is volcanic rock. Sometimes we can tell the age of the rock and the fossils in it within 100,000 years of the actual time, even if it happened 300 million years ago. (Don Lessem)

Q: How do scientists determine age from the bones?

A: We can't tell the age of dinosaurs by their bones. But you do get some clues both to the age of the individual dinosaur (they laid down rings as their teeth and bones grew, a bit like trees, sometimes, but we don't know if that was every year or not) and the time when that kind lived — by comparing it with other similar dinosaurs from times already known. (Don Lessem)

Q: How do scientists determine all of the dates that they give for when the dinosaurs lived, when humans came along, etc.?

A: We tell the age of dinosaurs from the rocks they were in or other better known and dated fossils found along with them or near them, particularly mammal teeth and small sea creatures. We can only date a rock precisely if it was made from a volcano — not by gradual buildup like most dinosaurs are found in. Volcanic rock contains some radioactive minerals in tiny amounts. These minerals break down over time at a very steady rate. By measuring how much of these minerals have broken down we can date such a volcanic rock to within 100,000 years of when it was made, even if it was many millions of years ago. Of course, such volcanic rock isn't always around dinosaur fossils. So often we have to guess from these other clues. (Don Lessem)

Q: What was the first dinosaur discovery? How and where was it found? What was its name? Was it a meat-eater? When did it become extinct?

A: The first dinosaur discovered and named was iguanodon in the 1820's in England, from a tooth brought to a medical doctor named Gideon Mantell. Iguanodon grew to more than 20 feet long and had a big spike on its thumb. But the first dinosaur scientists goofed and put the spike on its head. Iguanodon chewed plants. It lived about 120 million years ago or more in the early Cretaceous period. (Don Lessem)

Q: What is the largest dinosaur bone ever found?

A: The biggest single dinosaur bone, by weight, is one of the backbones of Argentinosaurus. One backbone was five feet by five feet and more than one ton in fossil weight. Of course it was lighter when the animal was alive before minerals entered into it to preserve it. The largest bone group ever found was the hip area of the Supersaurus, another four-legged plant-eater. Brigham Young University researchers dug it up about five years ago in Colorado. It is about six feet wide and up to eight feet tall. The biggest skull ever found was the eight-foot-long skull of torosaurus, a horned dinosaur, which ate plants near the end of dinosaur time in the American West. It was discovered by the Milwaukee Public Museum crews about eight years ago. (Don Lessem)

Q: How many complete dinosaur bone sets have been found?

A: Good question, and I'll be darned if I know the exact answer. One scientist estimated there are only about 2,100 good skeletons of any dinosaur in museums around the world. But a complete skeleton is another thing. It's not like a model kit that comes with all the parts included. When we are lucky enough to find whole dinosaurs it is usually because sand from a stream bottom or a sand dune has covered over the dinosaur soon after it died. But even then, the little bones of the tail are often washed or blown away. For instance, we have about 15 good skeletons of T. rex now, including two that are nearly complete. That's a lot compared to most dinosaurs, which are only known from a single tooth or bone. But we still don't have a complete T. rex. (Don Lessem)

Q: How many bones does a dinosaur usually have?

A: Most dinosaur skeletons have several hundred individual bones. (Tim Rowe)

Q: Have any new dinosaurs been discovered in the past year?

A: One named this year is Gasparainasaura, one of the few girl-named dinosaurs. It is named for a female scientist from Argentina. It is a small plant-eater from Argentina. (Don Lessem)

Q: What is the most recently discovered dinosaur?

A: Lots of dinosaurs are found every year. A new kind of dinosaur is named every seven weeks. The latest officially named is the giganotosaurus. It was a meat-eater even larger than T. rex and it was named in a scientific journal. Many other dinosaurs were found this summer but not yet named. In early November fossil scientists will report on these discoveries to each other in their annual meetings — this year at the Carnegie Museum in Pittsburgh. One new find that will be mentioned there is of a whole bunch of dinosaurs, about 12 kinds from T. rex's time, in South Dakota. Among them are pieces of some new raptors, bigger than those in Jurassic Park! (Don Lessem)

Q: How many bones did the T. rex have? More than we do?

A: Since we don't have a whole T. rex no one knows how many bones it had. But we do have most of the bones, so we could guess, even without the tip of the tail, if only anyone had thought to count them all. I never have and I don't have one handy. I'd guess it didn't have all that many more than us — just bigger. It had fewer fingers, only two, but many more bones in its tail, since we don't have one. And it had belly ribs, which we don't have, and more teeth (about 50). (Don Lessem)

Q: Where have most of the dinosaur remains been found in the world?

A: The U.S. is number one in kinds of dinosaurs found, though the single best place in numbers of species found is Dinosaur Provincial Park in Alberta, Canada, where some 37 kinds of dinosaurs have been found. Mongolia and Argentina are now sources of many interesting dinosaurs. (Don Lessem)

Q: Where is the most common place to find dinosaur bones?

A: The most common place to find bones is in an area where there is a lot of erosion and where there are not a lot of plants to obscure the ground. The deserts of the American Southwest, and large areas of the Rocky Mountains are rich areas in which to look for fossils. (Tim Rowe)

Q: Do they display real bones in museums?

A: In museums, bones are cleaned and cast and the copies attached to one another to make skeletons. The real bone is too rare to put out on display. We only have 2,100 good dinosaur skeletons in the whole world! (Don Lessem)

Q: When paleontologists find dinosaur fossils, do they get to stay in that area, or do they go to different museums?

A: If a scientist finds dinosaur bones, he can usually bring it back to his museum or university. If it's found on private land it belongs to the landowner. (Don Lessem)

Q: What is some of the latest equipment used to find dinosaur bones?

A: In recent experiments to find fossils, Geiger counters have been used, since uranium is sometimes concentrated in dinosaur bones and that causes a tick on the counter since it is a radioactive mineral. Shotguns have been blasted into the ground, and then hydrophones are used, (like microphones) to listen to the echo and to figure out if a fossil changed the pattern of the soundwaves. Ultraviolet cameras have been used since some dinosaur bones glow under ultraviolet light. Radar and other techniques have been tried. But none of these has yet proved to work well. The best way to find a dinosaur is still to walk around and look and find just a tip sticking out of the ground. Beneath it may be a whole dinosaur not yet eroded away by being on the surface of the ground. (Don Lessem)

Q: If there are no real dinosaur bones, skin, or organs, how do scientists know how much a real dinosaur weighed?

A: Scientists don't know how much dinosaurs weighed! They don't like to make those estimates, because they don't have enough information, but everyone wants them to guess. You can only guess based on how much modern land animals weigh for their size and scaling up for dinosaurs. The width of the skeleton and the heaviness of the bones help in the estimate as does the size of the dents in the bones made by where the muscles insert into it. That tells you a bit about how big the muscles were and so how much they weighed. But until we can get a live dinosaur up on a truck stop weighing scale we'll never know for sure how much it weighed. (Don Lessem)

Q: How can you tell if a dinosaur was a girl or a boy?

A: We can't tell boy from girl dinosaurs for sure. Some dinosaurs, like duckbills and horned dinosaurs, had one sex with much more fancy head gear, probably the males to attract females. But we don't know for sure. One sex on duckbills and T. rex and maybe other dinosaurs had bigger top of the tail bones. Maybe that was females to help pass eggs. And one sex was bigger, in T. rex and other dinosaurs. Maybe that was females, like in many birds and reptiles. But we don't know. (Don Lessem)

Q: Why did the parasaurolophus need bird hips when he walked on all fours? I read that dinosaurs with bird hips walked on two legs and could run quickly.

A: Not all bird-hipped dinosaurs ran on two legs. Parasaurolophus and other duckbills, as well as the earlier iguanodontid bird-hipped dinosaurs, were probably able to run on their hind legs or walk on all fours. There are other four-legged bird-hipped dinosaurs, such as the horned dinosaurs, or the ceratopsians. For larger dinosaurs, walking on four legs may have been a way to support their enormous weight. (Don Lessem)

Q: How many bones were found of the ultrasaurus?

A: We don't have much of ultrasaurus: a shoulder blade and possible back bone and maybe a few other bones. It could be just a giant new species of brachiosaurus. But it sure was big. (Don Lessem)

Q: Have any apatosaurus bones or fossils been found recently?

A: No new apatosaurus fossils that I know of, but then the quarries that produced them haven't been dug for a while. Excavation has stopped, as far as I know, at Utah's Dinosaur National Monument where some of the most famous apatosaurs were found. Wyoming, Utah and Colorado are all places where they've been found. There are probably lots more out there. Maybe one of you will have a chance to look for another one! (Don Lessem)

Q: How did you know to look for dinosaur fossils in Antarctica? How did you know exactly where to look?

A: I actually did not go to Antarctica just to look for dinosaurs. I was there looking for reptiles that lived early in the Triassic period, before the first dinosaurs evolved. We had found many fossils of these earlier reptiles on previous expeditions to Antarctica. However, we always look in new places for different types of fossils and that is how the dinosaurs were discovered. We search in areas where there are sedimentary rocks that have been deposited by ancient rivers, because that is where you usually find buried skeletons that have become fossils. It was along an ancient river channel buried in mudstone that we found the Antarctic dinosaurs. Now you know where to look, whether you are in Antarctica or any place else. (Bill Hammer)

Q: Have you ever found or worked with any caveman bones?

A: I think early human bones are neat, but I've never dug for them. I did write a book, The Iceman, about a 5,000-year-old mummy that was recently found in ice in Europe. He still had all his stuff with him, including a copper ax, fannypack and knife. It was a cool discovery. (Don Lessem)