Fossils and Dinosaurs
Grade 3 · Science · Study Guide
Discover how fossils form, what they tell us about ancient life, and what scientists have learned about dinosaurs.
A fossil is the preserved remains or traces of a once-living organism from long ago. Fossils can be bones, shells, teeth, footprints, or even impressions of leaves. They form when an organism dies and gets buried in sediment such as mud or sand. Over millions of years, the sediment hardens into rock and the remains are preserved.
Scientists called paleontologists study fossils to learn about ancient life. By examining the size and shape of bones, they can figure out how a dinosaur moved, what it ate, and how it behaved. Fossils also help scientists understand how life on Earth has changed over time.
Dinosaurs were a group of reptiles that lived on Earth from about 230 million years ago until about 66 million years ago. They came in many shapes and sizes, from the tiny Compsognathus (about the size of a chicken) to the massive Argentinosaurus. Some dinosaurs ate plants (herbivores) and others ate meat (carnivores).
The most popular dinosaurs include T. rex, a large carnivore with tiny arms and powerful jaws; Triceratops, a plant-eater with three horns on its head; and Brachiosaurus, a long-necked plant-eater that could reach tall trees.
Most scientists believe a large asteroid hit Earth about 66 million years ago, causing dramatic climate changes that led to the extinction of non-bird dinosaurs. However, birds evolved from a group of two-legged dinosaurs, so dinosaurs are not completely gone!
Key terms
- Fossil
- The preserved remains or traces of an ancient organism found in rock.
- Paleontologist
- A scientist who studies fossils to learn about ancient life on Earth.
- Sediment
- Small particles of rock, sand, or mud that settle in layers and can preserve fossils over time.
- Extinct
- Describes a species that no longer exists anywhere on Earth.
- Herbivore
- An animal that eats only plants; many dinosaurs like Triceratops were herbivores.
- Carnivore
- An animal that eats other animals; T. rex was a well-known carnivore.
Flashcards
- Fossil
- Preserved remains or traces of an ancient organism found in layers of rock.
- Paleontologist
- A scientist who studies fossils to understand life in the ancient past.
- Sediment
- Sand, mud, or other fine particles that settle in layers and can preserve fossils.
- Extinct
- When an entire species no longer exists on Earth.
- Dinosaur
- A group of reptiles that dominated Earth from about 230 to 66 million years ago.
- T. rex
- Tyrannosaurus rex, a large carnivorous dinosaur with powerful jaws and tiny arms.
- Triceratops
- A large herbivorous dinosaur with three horns and a bony neck frill.
- Asteroid
- A large rocky object in space; a massive asteroid impact is linked to dinosaur extinction.
Questions
What is a fossil?
- A type of rock found on the ocean floor
- The preserved remains or traces of an ancient living thing
- A living animal that has not changed for millions of years
- A type of dinosaur egg
Show answer
Answer: The preserved remains or traces of an ancient living thing
Fossils are preserved remains or traces of organisms that lived long ago, found in layers of sedimentary rock.
Paleontologists study fossils to learn about ancient life on Earth.
Show answer
Answer: True
Paleontologists are scientists who study fossils. They use what they find to reconstruct ancient ecosystems and track how life evolved.
A species that no longer exists anywhere on Earth is called ______.
Show answer
Answer: extinct
A species is extinct when every member of that species has died and none remain anywhere on Earth.
Triceratops had three horns on its head and ate plants. This makes it a:
- Carnivore
- Omnivore
- Herbivore
- Decomposer
Show answer
Answer: Herbivore
Triceratops ate plants, which makes it a herbivore. Its three horns were used for defense, not for hunting.
Modern birds are believed to have evolved from a group of dinosaurs.
Show answer
Answer: True
Scientific evidence shows that birds descended from theropod dinosaurs, meaning birds are technically modern-day dinosaurs.
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