You've probably seen pictures, models, or movies about dinosaurs that lived millions of years ago. But how do we know so much about these animals? How do we know what they looked like and how they lived? Since the early 1800s, scientists have been piecing together this mystery with fossils.
Fossils are the remains of ancient life. In order to become a fossil, the remains of a living thing must be buried quickly, usually in mud, sand, or volcanic ash. Over time, as the remains are buried deeper and deeper, the material around them hardens into rock. Minerals eventually replace the remains, turning them to rock too. Most fossils form from the hard parts of organisms such as teeth, shells, and bones. They also form from things a plant or animal leaves behind, like a footprint, a leaf print, and even eggs.
Fossils show us what Earth was like long ago. They give us a picture of ancient environments. Scientists compare fossils from different time periods to investigate how life on Earth has changed over time. Think of fossils like puzzle pieces. The more pieces you have, the easier it is to put them together and tell what the whole picture looks like. And sometimes when you find and add new pieces, the picture looks very different from how you thought it would be.
What must happen for something to become a fossil?
The word volcanic ash appears in the chunk above. The text mentions that remains can be buried in 'volcanic ash.' Ash comes from volcanoes. Why would volcanic ash be good for preserving fossils?
Have you ever put together a puzzle? How is finding and studying fossils similar to putting together puzzle pieces?
In 1923, a team of paleontologists from the American Museum of Natural History made a surprising discovery in Mongolia's Gobi Desert. They found three large rocks that turned out to be fossilized dinosaur eggs. Then they discovered another fossil nearby: a toothless dinosaur. The leader of the expedition, Roy Chapman Andrews, guessed that the dinosaur had been stealing the eggs from the nest. He named it Oviraptor (OH-vee-rap-tor) or 'egg thief.'
Seventy years later, in 1993, another team from the Museum found very similar fossil eggs in the same desert. One of the eggs held a fossil embryo, or developing baby dinosaur. It turned out to be a baby Citipati (sit-uh-PAH-tee), a kind of dinosaur very similar to Oviraptor. Later, the team discovered a fossil of an adult Citipati over a nest. It was brooding, or sitting on the nest, the same way birds do: with its arms spread to protect the eggs. And if its arms were covered with feathers, as scientists suspected, these wings would have shielded the eggs from heat and cold. Paleontologists realized that these dinosaurs nested like birds living today. These dinosaurs didn't steal eggs. They were caring parents!
When the discovery was made, the group of dinosaurs that includes Citipati and Oviraptor had already been named 'oviraptorids.' Even though scientists no longer think these dinosaurs were 'egg thieves,' the name stuck.
What did the 1993 discovery show about Oviraptor and its relatives?
Why did the name 'Oviraptor' stick even though it was wrong?
Have you ever thought someone did something wrong, but later found out they were actually helping? What happened?
Over 100 years ago, scientists started to notice similarities between birds and a group of dinosaurs called theropods (THERE-uh-pods). This group included Tyrannosaurus rex, Velociraptor, and Citipati. As new theropod fossils were discovered, the link with birds became even clearer. Scientists discovered that like birds, theropods laid eggs. And they walked on two feet with their legs directly underneath them. They also had three-toed feet with claws, an s-shaped neck, and hollow bones. Some even had sharp, bird-like beaks. And many theropods had feathers!
Citipati lived about 80 million years ago. These bird-like theropods grew to about nine feet long, with a toothless beak and feathered tail and front limbs. Because birds are so similar to these animals, scientists have placed them in the same group. Birds are theropods. This means birds are a kind of dinosaur! By piecing together fossils of extinct dinosaurs, we've learned that dinosaurs aren't extinct after all.
What is one similarity between birds and theropod dinosaurs?
The word extinct appears in the chunk above. The text says 'dinosaurs aren't extinct after all.' What does 'extinct' mean?
Birds are considered dinosaurs. Does this change how you think about the birds you see outside? Why or why not?