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Introduction Grade K Lessons Grade 1 Lessons Grade 2 Lessons Grade 3 Lessons Bibliography
Table of Contents
Lesson Overview
Teacher Background Information
Lesson Focus
Objective Grid
Lesson 1: Long Ago
Lesson 2: Extinction
Lesson 3: Fossils
-Two Legs or Four Legs
-Fossil Prints
-Fossil Hunting Lesson
-Fossil Matching
Lesson 4: Types of Dinosaurs
Lesson 5: Meat and Plant Eaters
Lesson 6: The Dinosaur's Life Cycle
Lesson 7: Nature and Change
Spanish Language Translations

Dinosaurs - Lesson 3: Fossils
ACTIVITY: Two Legs or Four Legs

Students construct sets of two, four and five objects.

Dinosaur models of two- and four-legged dinosaurs
Sorting trays

Tell students that all dinosaurs walked fully erect, unlike modern reptiles like lizards and crocodiles that walk on their bellies with their legs sprawling out from their sides. Dinosaurs are the only reptiles that walked like mammals.

Some dinosaurs walked on two legs, some on four. All four-legged dinosaurs were herbivores. All carnivores were two-legged, although some herbivores were two-legged as well.


  1. Students sort the dinosaur models into those that have two legs and those that have four legs. They count the legs and say that one plus one is the same as two; two plus two is the same as four.
  2. Students draw pictures of the four-legged dinosaurs and give reasons why these would be herbivores (plant eaters).
  3. Students draw pictures of the two-legged dinosaurs and give reasons why these would be carnivores (meat eaters).
  4. Students draw a set of three dinosaurs and say that three is one more than two, or two more than one.
  5. Students draw a set of five dinosaurs and say that five is one more than four, or four more than one, or three plus two.

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