Even with its neck lowered, the Diplodocus towers over the Eoraptor at the new David H. Koch Hall of Fossils.

Correction: The original article included incorrect information about when T. rex lived and about its fingers. T. rex lived 66 million to 68 million years ago and had two visible and one vestigial finger on each forelimb.

Of all the creatures that have walked, slithered, swum and soared around the Earth over the past, oh, 3½ billion years, dinosaurs are undoubtedly the coolest. That, in any case, is the consensus view of children, and it’s why the newly redesigned fossil hall at the National Museum of Natural History, opening Saturday, is likely to be the most visited room in one of the most visited museums in the world. We asked Matthew Carrano, the museum’s curator of dinosaurs, to tell us about the biggest and smallest specimens in the new exhibits.


This Diplodocus is the largest dinosaur in the exhibit.

Diplodocus

Weighing in at about 14 tons when it was alive, this adult Diplodocus didn’t need to worry much about the fearsome carnivores that it lived alongside, in what’s now Utah, during the late Jurassic period (about 150 million to 155 million years ago). With size as their primary defense, Diplodocuses had to grow up fast, Carrano says. “By the time they are 20, they are about this size,” he says. The Smithsonian’s Diplodocus skeleton is about 90 feet long, from tail to nose, and — as it’s currently posed — 13 feet tall.

1. Neck

Scientists once thought the Diplodocus used its long neck to browse treetops, but new research suggests the dinosaur didn’t raise its head much above shoulder height. So why bother evolving such a long neck? “Imagine a weed wacker with a long arm. A long neck might have been a great way to hoover up all the vegetation from one spot without having to walk,” Carrano says.

2. Teeth

Diplodocus used its peg-like teeth to strip leaves off plants. “And it probably had a massive gut for processing all that plant matter,” Carrano says.

3. Claw on front foot

No one knows what this one oversized claw was for, Carrano says, but it probably wasn’t self-defense, since this dinosaur could defend itself just by sitting on potential predators. “Maybe it helps them walk, by having a little bit of a grip,” he says.

4. Tail

Fossil evidence suggests the Diplodocus held its long tail high, rather than dragging it around. “We’ve found thousands and thousands of footprints of these animals and you never see a tail that has left a mark in the ground.” Powerful muscles may have even allowed the dinosaur to whip its tail at supersonic speeds, creating a loud, bullwhip-like sound.


This Eoraptor is the smallest dinosaur in the exhibit.

Eoraptor

One of the first dinosaurs to walk the Earth, the diminutive Eoraptor lived during the Late Triassic period, about 230 million years ago. It survived a climate change-triggered extinction event that killed off 76% of all species on the planet, and is part of the linage that includes the T. rex as well as modern birds. This cast of a South American specimen stands just 22 inches tall, representing an Eoraptor that probably weighed 20 to 25 pounds.

1. Teeth

The variety of teeth suggests that this critter was an omnivore. “As you go back in the mouth, they basically get less curvy and more triangular. And oftentimes you see that in animals that have a more varied diet, of both plants and meat,” Carrano says.

2. Hands

The Eoraptor has grasping, five-fingered hands, but you could probably only spot three of the fingers on a living specimen, as two were smaller and folded into the fleshy part of the hand. “Later dinosaurs specialize into a three-fingered hand,” Carrano says. “Birds today retain those same three fingers.”

3. Brain

Judging from the size of its brain, this little creature was not very sharp. “I wouldn’t say they were especially dumb, but most dinosaurs were about as smart as a frog is now,” Carrano says.

4. Legs

Why did the Eoraptor survive the Late Triassic extinction? “They have a very upright posture. Their legs are straight under their bodies, not out to the side like a crocodile, and that might have given them a little bit of an advantage in terms of speed. And being two-legged frees up your hands,” Carrano says.