As it fell onto the moist earth, the ash combined with water to create a gooey mud trap, like superthick quicksand. Before long, a small dinosaur called a ceratosaur wandered into the muck on its hind legs and couldn't break free. Another meat-eating dino spied easy prey and ran toward the helpless animal. But this was no free lunch! Both predator and prey sank to their doom in the "quickmud."
This scene may have played out again and again as at least 14 dinosaurs tumbled into three different mud traps. Now, more than 160 million years later, scientists have unearthed this dino graveyard—including fossils of the oldest known member of the tyrannosaur family. And the discovery is revealing ancient secrets from the age of the dinosaurs.
Lost in Time
Fossils have shown that the earliest dinosaurs lived about 230 million years ago and were only about the size of today’s German shepherds. About 145 million years ago, massive dinos such as the four-story-tall Brachiosaurus began to stomp the Earth. But what did dinosaurs look like in between?
"The mud pits are a real discovery," says dino expert James Clark, who participated in the dig. "There are very few dinosaur fossils from this time in the middle, when the animals started transitioning into giants."
As scientists chipped away at the remains of the mud pits—now giant blocks of rock they found one unusual creature after another. "They were stacked up like pancakes," Clark says.
Among other fossils, they uncovered a bizarre toothless meat-eater called a ceratosaur; an ancestor of the horned dinosaurs—such as Triceratops—named Yinlong; as well as ancient turtles, mammals, and crocodiles.
But the most incredible discovery of all is a new two-legged predator with a Mohawk-like crest on its head. Named Guanlong, Chinese for "crested dragon," it weighed just 165 pounds (74.8 kilograms). But parts of the animal's skull and a telltale ridge in its hip bone look strikingly similar to gigantic tyrannosaurs that lived about 100 million years later—including the 15,000-pound (6803.8-kilogram) Tyrannosaurus rex.
Digging Up Answers
Now these discoveries are helping to solve many dinosaur mysteries. You probably know that Tyrannosaurus rex had surprisingly wimpy arms and used its terrifying teeth to grab prey. But did its ancestors have more powerful arms? Yes. Guanlong's muscular limbs show that early tyrannosaurs probably snatched prey with their arms.
Ferocious Triceratops fought off enemies with its three dangerous horns and a bony frill around its neck. Did the beast's smaller ancestors have horns, too? No. "Yinlong may not have needed big horns because it was smaller and could probably flee from predators more easily," says National Geographic's dino expert Josh Smith.
And these finds are just the beginning. As the dig continues, the strange creatures of the Gobi death pits could help scientists rewrite the history of dinosaurs.