Dear Addison,

Before humans even had a word for dinosaur, they were digging up dinosaur bones. When one paleontologist dug up a big dinosaur leg bone, he wondered if it belonged to a giant human. A woman who dug up some large teeth wondered if they belonged to a huge iguana.

illustrated cartoon gray cat, Dr. Universe, wearing a white lab coat, yellow pants, and a crimson shirt with Washington State University logoScientists now think the giant leg bone probably belonged to a dinosaur called Megalosaurus. The teeth belonged to an Iguanodon. It turns out, the dinosaur bones people dig up aren’t really bones anymore—they have fossilized. Over the course of millions of years, the minerals in the bones have become more like rock.

I visited my friend Cynthia Faux to find out more about dinosaur bones. She’s a veterinarian at Washington State University who is curious about dinosaurs and birds—the dinosaurs of today.

“There might be a different number of bones even between a T-rex, stegosaurus, triceratops,” Faux said. “It may have depended on their species.”

Even the number of bones in humans can vary, Faux adds. Some experts debate which bones to include in the human skeletal system. For example, some say we should include sesamoids, tiny bones that are embedded into tendons. Still, most agree humans usually have around 206 bones.

T-Rex also may have had about 200 bones. At least that’s how many bones we know about so far. A couple decades ago, a woman named Sue Hendrickson came across a lot of T-Rex bones in South Dakota. The dinosaur was also given the name “Sue.” Today, Sue—the dinosaur—is housed at the Field Museum in Chicago

Sue is one of the dinosaur skeletons we know the most about. It’s about 90 percent complete. There are still bones we don’t have, including some of the smaller bones in Sue’s tail.

According to the museum, Sue’s skull is almost five feet long. The whole dinosaur is about 42 feet long. Sue has 24 rib bones and also something called gastralia. The gastralia are kind of a “bone basket” scientists think might have helped Sue breathe—but they still aren’t sure exactly where those pieces go.

Dinosaur skeletons actually have a lot in common with birds. When we compare some bird and dinosaur bones we see a lot of similarities in claws, beaks, necks—and in the case of Sue the dinosaur, even a kind of wishbone.

If you wanted to look for dinosaur fossils, you’d probably want to pack your chisel, a rock hammer, brushes to dust off debris, a tape measurer, and a map or GPS. You’ll also want to know where to look. Humans have discovered quite a lot of dinosaur bones in China, Argentina, and North America—especially in Utah, Wyoming, Colorado and Montana. Who knows? Maybe one day you’ll set out into the field and help us learn more about dinosaur bones.

Dr. Universe