The Largest and Smallest Dinos Ever (Maybe)

Its name is Supersaurus. No joke. Super — as in huge, powerful, extreme.

And, wow, was it ever extreme! This super dinosaur measured at least 128 feet — possibly even 137 feet — from its snout to the tip of its tail. That's longer than three and a half full-sized school buses lined up end to end. And it’s probably longer than any other creature that ever walked the Earth.

Supersaurus lived about 150 million years ago during the Jurassic period in an area that’s now Wyoming and Colorado. It was a sauropod, a type of plant-eating dinosaur that walked on all four legs and had a small head at the end of a really long neck, a massive body, and a long, whip-like tail. Supersaurus’s tail alone was 60 feet long — the length of a bowling alley — and its legs were 12 feet tall. An adult human could have ridden a bike under its belly without ducking.

You’d think that a dinosaur that long — and with that cool name — might be the biggest dino ever. But, no. Scientists agree that Supersaurus was the longest dinosaur, but not the largest overall.

So who was?

Meet Argentinosaurus, a super heavyweight that tipped the scales at somewhere between 66 to 100 tons — twice the weight of Supersaurus and about the same as an entire herd of 20 or so African elephants. Those amazing figures clearly make Argentinosaurus the champ! Right? Well, probably.

Unless, that is, Patagotitan was even larger, like some scientists think. Or maybe the mysterious Amphicoelias dwarfed them all. Then again, a new sauropod — still unnamed — that paleontologists began digging up in 2012 in Argentina looks like it was even larger.

So why don’t we know for sure?

First, there’s the problem of how you measure something that’s been extinct for millions of years. It is extremely rare to find anything close to a complete dinosaur skeleton. So most dinosaurs, especially the really big ones, are identified by just a few bones — sometimes by only one bone! It’s clear that sauropods, the long-necked, four-legged plant eaters, towered above other dinosaurs, including monstrous meat-eaters like Tyrannosaurus rex and Spinosaurus. But it's hard to tell which one was the largest of all.

Scientists do their best to estimate the dino’s size and appearance by comparing it to similar dinosaurs and other animals. They take all the information they have and use formulas and 3D computer models to come up with an estimate. It works best when paleontologists find the upper arm bone and thigh bone from the same sauropod, because those bones are the most important for an animal when it comes to movement and supporting its weight. As scientists find more fossils of the same dinosaur, they can improve their estimates.

But even when we think we have all the information on dinos sorted out, scientists make new discoveries that often change a lot about what we thought we knew. Scientists learned, for example, that sauropods’ neck bones were filled with air to keep them light — instead of marrow like in mammals’ bones. So you can’t say, Well, that dinosaur was about ten times bigger than an elephant, so we’ll just multiply an elephant’s weight by ten. That won’t work, because the two animals aren’t built alike. As paleontologist Kristi Curry-Rogers told the publication Scientific American, “With nothing quite like sauropods today, our work on these creatures is akin to studying aliens.”

Sometimes our understanding of dinosaurs changes when paleontologists find a new fossil, like the giant sauropod recently discovered in Argentina. Based on its hip, shoulder and tail bones, the sauropod — which lived 98 million years ago during the late Jurassic to early Cretaceous periods — was possibly bigger than Argentinosaurus and Patagotitan. But scientists haven’t found its upper arm and thigh bones, so they don’t know for sure.

Scientists also might learn something new about an old fossil. Paleontologist Brian Curtice uncovered mistakes that a fossil finder had made 50 years ago when Supersaurus was first discovered. He was able to get a better estimate of the dinosaur’s length by re-examining the old fossilized bones, identifying new ones from the same animal, and comparing the skeleton to others found more recently.

It’s not any easier figuring out which dinosaur claims the title of “smallest dinosaur ever” — at least among extinct dinosaurs. (If you want to be really technical, scientists consider birds to be “avian dinosaurs.” So the smallest dinosaur would be the bee hummingbird, which lives only in Cuba. It’s about two inches long and weighs as much as a dime.)

Among extinct dinosaurs, one of the cutest little dinos contending for the honor of “smallest ever” was found back in the 1970s in Argentina. The little dinosaur fossil was around six inches long (not including its tail), about the size of a small lizard. Scientists named it Mussaurus from the Latin word mus, which means “mouse.” They may have been a bit embarrassed later when they realized that their fossil was actually a baby, and the adult “mouse-dinos” grew to be roughly the size of a minivan.

Other dinosaurs grew no bigger than chickens or turkeys. One of the smallest dinosaurs was Parvicursor, which means “slender runner.” True to its name, the slim little dinosaur, which lived during the late Cretaceous period around 72 million years ago in what is now Mongolia, had long, skinny legs. It measured only 15 inches long and weighed about as much as a packet of six wooden pencils. Even smaller was a flightless, feathered dinosaur named Eosinopteryx, which wasn’t even a foot long. Living in what is now northeastern China during the Jurassic period, Eosinopteryx looked a little bit like a bird — except with a short, toothed snout and skinny tail.

Scientists continue to unearth new dinosaur fossils, learn more about existing fossils, and improve their techniques for estimating the size and weight of dinosaurs. As they do, we’ll learn more about these amazing creatures — both whoppers and pipsqueaks alike — and find new record breakers. The folks at Guinness World Records will have a tough job keeping up!