Cretaceous Period
The Cretaceous Period was the most recent period of the Mesozoic Era, ending about 65 million years ago.

Dinosaurs were reptiles that lived on the Earth for about 170 million years, then became extinct.

The complete disappearance of a species, usually caused by environmental conditions, is called extinction.

The preserved remains of an organism that lived long ago are called fossils.

Mesozoic Era
The interval of the Earth's history from about 230 million to 65 million years ago is known as the Mesozoic Era.

The Ornithischia were plant-eating dinosaurs with hipbones that resemble the hipbone arrangement of modern birds.

Reptiles are vertebrates that have dry scaly skin and breathe by lungs, among other characteristics.

The Saurischia were dinosaurs with hipbones similar to those of modern crocodiles. The group included both plant- and meat-eating dinosaurs.

The fiercest dinosaurs were the therapods, two-legged, flesh-eating members of the Saurischia.

From 230 million to 65 million years ago, reptiles called dinosaurs lived on the Earth. They varied tremendously in size and shape. Some were about the size of a dog but others were huge, weighing many tons. The largest species ate plants, but others were flesh eaters. Most were four-legged, but many walked and ran on their hind legs only. Dinosaur fossils have been discovered nearly worldwide, and major new finds are continually reported. These fossils include bones, eggs, footprints, and even traces of feathers. Based on their study of fossils, scientists have been able to classify dinosaurs into two main groups, the Saurischia ("lizard hips") and the Ornithischia ("bird hips"). Also using fossils as a guide, scientists have created life-size models that show how different events in a dinosaur's life may have occurred. But many mysteries remain. One of the biggest concerns the disappearance of the dinosaurs. Scientists have proposed various theories to account for the extinction of these fascinating animals, but none have been conclusively proven.

Here are some topics to explore that relate to dinosaurs. Looking at the articles, images, and other materials in this Research Starter may give you more ideas. Each topic has one or more articles to start you on your research, but remember that it takes more than one article to make a research paper. Continue your research with our list of articles below.

Fossil hunters.
Fossil Record

General characteristics of dinosaurs.

The earliest dinosaurs.
Mesozoic Era

The biggest dinosaurs and how they lived.

Why dinosaurs became extinct.

Dinosaurs and birds: Are they related?
Fossil Record

Cretaceous Period
Fossil Record
Mesozoic Era

Welcome to UCMP!
Provides history of paleontologic science and information regarding vertebrate flight and the geologic time scale. Also includes images and introductory text on groups within various taxonomic classes.

Field Museum of Natural History online exhibit includes movies, images, text, sound, games that provide an excellent overview of life in the era of dinosaurs.

Dinosauria On-Line
Dinosauria On-Line offers dinosaur picture gallery, dictionaries, taxonomic information, geological data, maps, and explanations of dinosaur names, as well as a style guide for writing about Paleontology.

Mary Anning, Finder of Fossils
Brief biography of renowned 19th-century fossil hunter Mary Anning. Maintained through the San Diego Supercomputer Center.

Early Dinosaur Discoveries in North America
Discusses the 19th-century North American fossil discoveries that led to the early study of dinosaurs. Maintained by the University of California Museum of Paleontology.

Frank Potter's Science Gems: Earth Science
Dozens of sites for earth science education are identified by category, subcategory, and grade level by physicist and educator Frank Potter and his associates. A treasure trove for teachers, parents, and students. Very easy to navigate. Recommended.

The Talk.Origins Archive
An informative Web site with several articles and essays and FAQs about evolution, creationism, and the details.

Mary Anning (1799–1847)
Biography of renowned 19th-century fossil hunter Mary Anning. Includes links to pertinent Web sites, including some on ichthyosaurs. Maintained by the University of California Museum of Paleontology.

Paleontology Without Walls
The University of California Museum of Paleontology provides an interdisciplinary look at natural history, biology, paleontology, phylogeny, evolution, and related areas. Highly illustrated and highly recommended, especially for teachers and students.

Geology and Geologic Time
Exhibit and text from UCB Museum of Paleontology provides an overview of geologic time periods.