Dr. Diego Pol’s three essays explain how scientists map evolutionary changes through diagrams called phylogenetic trees in order to figure out how species are related to one another and when different traits emerged. He starts with an overview of the dinosaur family tree, highlighting the major groups and the features that distinguish them. Then he explains the basic evolutionary changes that occurred within each group over millions of years. And finally, he tells the exciting story of how he and colleagues discovered one of the largest dinosaurs that ever lived. Videos show how the titanosaur was discovered, prepared, and finally mounted at the American Museum of Natural History. This week's assignment gives learners the opportunity to examine the characteristics of a fossil and construct an evidence-based hypothesis for its phylogeny.

The three essays this week, written by Dr. Norell with guest author Dr. James Napoli, explain what extinct dinosaurs were like when they were alive: what they looked like, how they maintained their bodies, and how they used their senses. Norell and Napoli explain how these discoveries were made through modern paleontological techniques such as studying living analogues to make inferences about how extinct animals lived. Guest author Dr. Amy Balanoff presents a case study of Citipati osmolskae to illustrate how she and other paleontologists study the fossil skulls of ancient dinosaurs to hypothesize about dinosaur behavior. In this week’s video Norell and Balanoff discuss commonalities between living birds and their extinct ancestors. In this week’s assignment learners will observe trackways, collect data on foot length and stride length, and then make inferences about behavior from data analysis.

This week, four guest scientists share their research into how dinosaurs moved and reproduced. First, Dr. Matteo Fabbri explains how paleontologists draw on evidence from living birds and reptiles to infer how dinosaurs hatched and cared for their young. Then Dr. Jasmina Weimann takes us on her personal journey of discovery about the color of dinosaur eggshells. In the next essay, Dr. John Hutchinson explains how he examines fossil bones and trackways, and then uses computer models to hypothesize how dinosaurs walked and ran. And in the final essay, Dr. Emily Rayfield explains how she uses computational methods that apply physical principles to test and deduce the feeding behavior of non-avian dinosaurs. Videos help learners visualize what dinosaurs looked like and how they grew. In this week’s assignment, learners will use images of authentic growth rings to age dinosaurs and construct growth curves.

The guest author this week is Dr. Greg Erikson, a paleontologist who studies population biology, the field that addresses questions such as how long dinosaurs lived and when they reached reproductive age. The first essay picks up on the assignment from the previous week, explaining how scientists analyze patterns in bone growth to infer the age of a dinosaur when it died. The second essay explores how scientists use growth curves to explore how dinosaurs got so big, or so small. The third essay explains how we can obtain a clearer picture of how these animals lived by examining demographic data (i.e., how many dinosaurs lived together, how many were sexually mature, at what age they died). A video features Dr. Aki Watanabe discussing the lifespan and growth pattern of the famous T. rex, from fluffy chick to tyrant king.

In this final week of the course, learners will pivot from investigating how non-avian dinosaurs lived to exploring how they went extinct. In the first essay, Pol compares theories about what caused the great dinosaur extinction 66 million years ago. In the second essay, he digs deeper into that extinction event to address questions such as: Why did some animal species survive when so many others did not? In the final essay of the course, Dr. Pol answers the question: How do we know what we know about the K-T extinction, using the Tanis site in North Dakota as a case study to answer that question and more.