What is a dinosaur?
Dinosaurs are a group of reptiles that lived during the Mesozoic Era. Dinosaurs have certain features in their skeletons, such as the number of holes in their skulls and the way their teeth fit into their jaws that make them different from other reptiles such as lizards or turtles. Dinosaurs also differed from other reptiles in the way that they stood. Other reptiles have sprawling or semi-erect postures where the elbows and knees pointed out to the sides. Dinosaurs had an erect posture—their legs were directly underneath their bodies. In that way, the legs more efficiently supported the weight of the body. Mammals also have an erect posture.
Dinosaurs lived only on land. The flying reptiles called pterosaurs, were not dinosaurs. Large prehistoric swimming reptiles, such as plesiosaurs and mosasaurs were not dinosaurs either.
What is the Cretaceous Period?
- The Cretaceous period, part of the Mesozoic Era took place 145 to 66 million years ago.
- Many organisms diversified and landmasses separated into some of the continents we recognize today. This allowed dinosaurs to evolve more independently in different areas of the earth.
- Sea levels rose and fell, and sediment built up along with many single-celled algae and other fossil skeletons. This is how much of the chalk we use today was formed, with the term Cretaceous coming from the Latin word for chalk - creta.
What happened during the Cretaceous Period?
- During this time, the first snakes evolved.
- The first flowering plants developed, and with that many pollinators like bees and other insects.
- During the Cretaceous Period, there were many famous dinosaurs including Velociraptor, Talarurus, Triceratops, Protoceratops, Oviraptor, and Alamosaurus.
What makes a T. rex unique from other dinosaurs?
- The Tyrannosaurus rex roamed in the late Cretaceous period, from around 68-66 million years ago.
- These dinosaurs have powerful jaws with around 60 teeth, each tooth nearing 8 inches long. Its bite was around 10 times that of an alligator.
- This dinosaur was a hunter and scavenger, with a large part of the brain dedicated to its sense of smell to locate prey.
- They likely lived up to 28 years, averaging 40 feet in length and 12 feet in height.
- The speed of the T. rex is up for some debate, but scientists estimate it was a slow runner, probably similar to the speed of an average human runner. They were bipedal and balanced its large head and heavy tail over 40+ vertebrae. Their small arms were still very powerful and featured two clawed fingers.
- These dinosaurs lived in what is now western North America, Canada, Montana, and South Dakota.
- The first discovery of this dinosaur was made in 1902 by Barnum Brown, a curator of the Department of Vertebrate Paleontology at the American Museum of Natural History in Montana. In 1905, the president of the museum, Henry Fairfeild Osborn, gave this dinosaur the name Tyrannosaurus rex, “the tyrant lizard king”
Famous T. rexes in the World
- Victoria the T. rex was discovered in Faith South Dakota in 2013
- She is 40 feet long and 12 feet tall, weighing 21,000 lbs
- Estimated to have died 18–25 years old
- Victoria is the second most complete T. rex thus far
- Sue, the T. rex was discovered in Faith South Dakota in 1990
- She is 40 feet long and 13 feet tall, weighing around 18,651 lbs
- Sue is considered the most complete T. rex discovered thus far
- Scotty, the T. rex was discovered in Canada in 1991
- He is 42 feet long weighing 19,555 lbs
- Estimated to have died in his early 30’s
- Scotty is the heaviest male T. rex that has been discovered
- Stan, the T. rex was discovered in the Hell Creek Formation near Buffalo in South Dakota
- Stan is nearly 40 feet long and 12 feet tall
- Trix, the T. rex was discovered in Montana
- She is 39 feet long and 13 feet high, weighing around 10,000 lbs
- Trix was recently touring Europe through Pariz, Barcelona, and Lisbon
How is a dinosaur fossil formed?
Only a tiny fraction of all the animals that have ever lived are preserved as fossils. There are many things that happen to a dead animal that make fossilization unlikely. The body decomposes; scavengers pull the body apart and devour it. Wind and rain can destroy the body. But in rare, special circumstances, a dead animal is buried rapidly before any of these things can start to destroy the body. An animal that dies in or near water is more likely to be buried quickly by sediments in the water. Over thousands, even millions, of years, minerals contained in groundwater can be deposited within the animals’ bones. The minerals make the bone heavier and it feels like rock. This is what people mean when they call something “petrified.” Paleontologists call this process permineralization and replacement.
Grand Canyon National Park. Geology Lesson Plans. United States Department of the Interior National Park Service Grand Canyon National Park.
The Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. 2013. Oceana Books. Marshall Editions.