Big dinosaur questions
Picture a big yellow school bus. Now line up two more behind it. The biggest dinosaur that scientists know well was even longer than that.
Here are the giants, how you weigh a dinosaur nobody has ever seen, and the tiny dinosaurs at the other end of the scale.
I'm as long as two school buses. The biggest dinosaur ever was longer than THREE.
Drawn to scale
Every picture here is drawn to the same scale, nose to tail. The dashed lines are school buses: one big yellow school bus is about 12 meters (40 feet) long. Find T. rex, then find yourself at the bottom.
There's a free size poster of this chart to print for your wall.
The titanosaurs
All four were titanosaurs, long-necked plant-eaters from what is now Argentina, in South America. They were the biggest animals that ever walked on land.
Patagotitan
Lots of bonesSay it: PAT-ah-go-TIE-tan · “titan from Patagonia”
37.5 m (123 ft) long · 57 tonnes (63 US tons)
One of the most complete giant titanosaurs ever found, so scientists are fairly sure of its size. It weighed more than nine African elephants.
Argentinosaurus
A few bonesSay it: AR-gent-EE-no-SORE-us · “Argentina lizard”
35 m (115 ft) long · 70 tonnes (77 US tons)
Only some leg bones, a few backbones and ribs have been found. It was probably a little shorter than Patagotitan, but heavier: about as heavy as twelve elephants.
Puertasaurus
Four backbonesSay it: PWER-ta-SORE-us · “Puerta and Reuil's lizard”
30 m (98 ft) long · 50 tonnes (55 US tons)
That's all anyone has found, and scientists still think it was one of the biggest titanosaurs.
Dreadnoughtus
Scientists disagreeSay it: dred-NAW-tus · “fears nothing”
26 m (85 ft) long · 22 to 59 tonnes
The first guess said over 59 tonnes, heavier than a Boeing 737 airplane. A newer way of working it out said only 22.
You might know Diplodocus, another famous long neck. Patagotitan was half as long again, and four times as heavy.
How do scientists know?
Nobody has ever put a dinosaur on the scales. When scientists find most of a skeleton, measuring it is the easy part. But for the biggest dinosaurs they often have only a few bones. Then they look for a close cousin whose whole skeleton is known, and guess that the missing parts were the same shape.
For the weight, there's a clever trick. In animals alive today, measure around the upper arm bone and the thigh bone, add the two together, and you can work out how heavy the animal is. Scientists can try the same with dinosaur bones, but nobody can be sure it works for giants.
That's why sizes change when new bones turn up, and why different books give different numbers. For Dreadnoughtus, one way of working it out said 59 tonnes and another said 22.
Try this at home
One Patagotitan thigh bone is 2.38 meters (7 feet 10 inches) long. Lie down on the floor and ask a grown-up to mark where your head and feet are. The bone is about two of you.
Or outside
With a long tape measure, mark out 12 meters for a T. rex, then keep going to 37.5 meters for Patagotitan. It's a LONG way.
The biggest meat-eater
The long-necked giants all ate plants. The longest meat-eating dinosaur scientists know of is Spinosaurus. Here's Katia's fact from the last page of Dinosaurs Are Back:
Spinosaurus was even bigger than Tyrannosaurus rex! It could grow up to 15 meters (49 feet) long, weigh 20 tons, and swim like a crocodile!
Not even close. Brontosaurus was one of the long-necked giants, a close cousin of Apatosaurus, and Apatosaurus grew up to 23 meters (75 feet) long. T. rex was about 12 meters (39 feet). Next to them, T. rex was the small one.
Heavier than any dinosaur
Yes. A blue whale can weigh up to about 150 tonnes (330,000 pounds). That's more than twice as heavy as Argentinosaurus, maybe the heaviest dinosaur of all. The blue whale is the biggest animal that has ever lived, and it's alive today.
The biggest animal ever lives on tiny shrimp called krill, which is the first clue in this riddle.
Riddle · who am I?
I'm bigger than a dinosaur, the biggest of all,but my favorite food is tiny and small.
I breathe through a hole on the top of my head,and I sing long songs in my deep ocean bed.
whale (the blue whale)!
The clue explained: The blue whale is the biggest animal that has ever lived, and it eats tiny shrimp called krill. (NOAA Fisheries)
Dinosaur eggs
Smaller than you'd think. In 2023 the Natural History Museum in London showed off a titanosaur egg that is 69 million years old and about the size of a grapefruit. The baby that hatched out of it grew into an enormous titanosaur.
Eggs? Don't talk to me about eggs. My baby brother Fino was still inside his when he went missing!
Spike, the young Triceratops from Dinosaurs Are Back
the grown-upThe other end of the scale
Nobody knows for sure. One of the smallest ever found is Microraptor (say it: MIKE-roe-rap-tor, “tiny plunderer”), about 0.8 meters (2.6 feet) from nose to tail, and about as big as a crow. It had feathered wings on its arms AND its legs. And another feathered dinosaur, Anchiornis, may have been even smaller: the biggest one found is only about 62 centimeters (2 feet) long. More about Microraptor
But the smallest dinosaur of all is alive right now. Birds are dinosaurs, and the smallest bird in the world is the bee hummingbird from Cuba: about 5.7 centimeters (2¼ inches) long, and lighter than a dime.
The biggest of Spike's ten, in your roomApatosaurus is the longest dinosaur in the book. Ours is made small enough for a living room: open it on a phone or tablet and tap “See it in your room”.Apatosaurus in 3D →Free, no sign-up
“How big were they?” on one page: Patagotitan, Apatosaurus, T. rex, a school bus, a turkey-sized Velociraptor and you, all drawn to the same scale. Stick it on the wall at home or in the classroom.
The black and white one is for coloring in, and a class of 25 kids lying head to toe still wouldn't reach the end of Patagotitan.
Free for home and classroom use. Please share the link to this page rather than the file.
Questions kids ask
Keep asking
Which flying dinosaurs were real dinosaurs?Pteranodon wasn't a dinosaur. But one kind of flying dinosaur is still around today.Find out →
Is Brontosaurus real?Scientists took its name away in 1903. In 2015 they gave it back.Find out →
Which long neck dinosaur is which?They're called sauropods. How to tell them apart, and which one had the longest neck of all.Find out →
What was the fastest dinosaur?Probably one that looked a lot like an ostrich. And the fastest dinosaur of all is alive today.Find out →Or meet all ten dinosaurs from Dinosaurs Are Back, each with a fun fact and a riddle.
The book · ages 6 to 10
Ten dinosaurs, from a turkey-sized Velociraptor to a giant Apatosaurus, and every one of them steps off the page with a phone or tablet.
Katia's facts are from the last page of Dinosaurs Are Back. Everything else was checked on these pages on September 27, 2026.
Picture credits