The guiding question of this investigation is, How should we classify the unknown organisms? In this lesson, the goal is to figure out how to classify an unknown animal based on the type of food it eats and how the structure of an animal’s skull is related to the type of food it eats. To accomplish this you will need to make observations and take measurements about the location of the eyes, the size of the jaw, and the shape of the teeth for six different animals. The Teacher Notes provide connections to the standards, a timeline, safety notes, information on materials and preparation, and step-by-step instructions for facilitating the lesson and assessing student outcomes. After the Teacher Notes, you will find classroom-ready reproducible pages in the form of an Investigation Handout and Checkout Questions. Before you begin the lesson, we recommend reading Chapters 1 and 2, which are in this book selection. Chapter 1 provides an overview of Argument-Driven Inquiry (ADI) with an explanation of what happens during each of the eight stages of ADI, which are the same for every ADI investigation. Chapter 2 focuses on the investigations and how to use them, not to replace an existing science curriculum, but rather to function as a tool that teachers can use to integrate three-dimensional instruction into their existing curriculum. Also included in the book selection are the Table of Contents, Preface, Acknowledgments, About the Authors, Introduction, and Index.