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Dinosaurs: the Smallest to the Largest

Answers to common questions about the size of dinosaurs

  • Grades: 3–5, 6–8

Q: Which dinosaur is the largest?
A: The biggest dinosaur is probably ultrasauros. We only have a few bones of this late Jurassic (140 million years ago) plant-eater from Colorado but they show an animal that was six stories high and may have weighed more than 50 tons. Recently, a four-legged plant-eating dinosaur was found in Argentina, Argentinasaurus which may have been even heavier. If it was a brachiosaur like ultrasauros, it probably was the biggest. But if it was a titanosaur, another kind of big plant-eater common in South America, it wouldn't have been so bulky.

Q: What was the smallest dinosaur?
A: The smallest dinosaurs we know only from footprints. It was a meat-eater 200 million years old from Nova Scotia the size of a little robin. But maybe that was only a baby. As for full grown fossil dinosaurs, the smallest are the little bird-hipped plant-eaters like Lesothosaurus which were the size of big chickens. Compsognathus, a meat-eater the size of a turkey, is often called the smallest, but that was information based on a skeleton that belonged to a young not yet full grown animal.

Q: Which dinosaurs were bigger — plant-eaters or meat-eaters?
A: Plant-eaters by far. T. rex and giganotosaurus, the biggest meat-eaters, were seven or eight tons and 45 feet long. The biggest plant eaters were 100 tons and 110 feet long!

Q: How do dinosaurs grow so big?
A: We don't know why they got so big. It could be that there was more oxygen, more nutritious food. But we'll probably never know why they got bigger than any animals before or since.

Q: How big did dinosaurs get? How big are their bones?
A: The biggest dinosaurs were the size of a school — six stories high and half a football field long. The smallest were the size of a chicken. The average dinosaur was as big as your car. The biggest dinosaur bones, like the hips of supersaurus, were eight feet wide.

Q: How tall were dinosaurs?
A: We don't measure dinosaurs by height, since they didn't stand up straight. (They leaned forward.) So we go by their length. But the tyrannosaurus and other large meat-eaters, called carnosaurs, were large. Sauropods, the four legged plant-eaters, were the largest of all, up to 150 feet long and 6 stories high. Two-legged plant-eaters could be large or small, like the 40-foot duckbills or the tiny hypsilophodonts, which were not much bigger than chickens.

Q: How heavy and how tall was gigantosaurus?
A: I figure you are asking about giganotosaurus, the newly named biggest of all meat eaters. The name means giant of the south. From most of the skeleton it is estimated to be about 46 feet long and 8 tons in weight. We don't measure dinosaurs by height since they didn't stand tall like people. Meat-eaters leaned forward with their tails held high, so they were nearly horizontal over their hips. Don't confuse the giganotosaurus with the gigantosaurus. The gigantosaurus is a big plant-eater with four legs, like brachiosaurus. It is known from just a few bones from England found more than a century ago.

Q: How tall was the T. rex?
A: T. rex was at least 12 feet tall but it didn't stand tall like we do. Instead it leaned forward with its tail up nearly as high as its lowered head.

Q: How long was the struthiomimus?
A: Most species of dinosaurs came in many sizes, from youngsters to adults, and some adults were bigger than others. Perhaps females were bigger than males as with many birds and reptiles. And we don't have many complete dinosaur skeletons to measure from. So, I'd say 12 feet from the books I've read, but it probably varied.

Q: How did brachiosaurus get so big by eating plants and not meat?
A: Plant-eaters got far bigger than meat-eaters maybe because they needed huge bellies to digest all that tough plant food. You can make a good diet from vegetables.

Q: Was a triceratops really as big as a house?
A: Triceratops wasn't as big as house, more like a garbage truck — about 20 feet long.

Q: In the book The Biggest Dinosaurs by Michael Berenstain, it says that the seismosaurus, found in Mexico, might be larger than the ultrasauros. Do you know if this is true?
A: Ultrasauros was the biggest we know, but we only know it from a few bones. It appears to be a brachiosaur, which was giraffe-like and heavily built. Seismosaurus was indeed longer, the longest we know, and we know it from a whole back end. It was a diplodocus relative, a longer-bodied animal with a whip tail but not so heavily built. It comes from New Mexico.

Q: Which Mesozoic period had the smallest dinosaur ?
A: The smallest dinosaurs were probably from the late Triassic and early Jurassic. That's where we find the smallest ornithischian dinosaurs. Dinosaurs got biggest in the late Jurassic and Cretaceous periods.

Q: What dinosaur had the biggest head?
A: The dinosaur with the biggest head was torosaurus, "bull lizard," a horned dinosaur related to triceratops. Torosaurus lived in the American West 65 million years ago. It had a skull eight feet long, longer than any animal on land ever.

Q: How big was the heart in a brachiosaurus?
A: We don't know how big the hearts were on any dinosaurs since soft parts of the inside of their bodies don't preserve as fossils. It is likely that brachiosaurus and other big four-legged plant-eaters had huge hearts since they had to pump blood all over their vast bodies up their long necks. I'd guess their heart was larger than you are.

Q: If there are no real dinosaur bones, or 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 helps to estimate weight, as does the size of the dents in the bones where the muscles insert into it. That tells you a bit about how big the muscles were and 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!

Q: How much did the T. rex weigh?
A: T. rex weighed at least seven tons by most estimates.

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