Igniting excitement for physics in our students is a goal of every instructor. In this paper, we discuss a unique example of the concept of density, a subject that is rarely viewed as intriguing by students. By combining a problem involving dinosaurs and an effective density, our students' interest is often captured through calculating an estimated mass of hatchling tyrannosaur and sauropod dinosaurs. This unusual kind of density also provides an interesting backdrop for students to test their understanding of density. We also discuss how this result can be used to learn more about dinosaurs.