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A new film offers a glimpse into the Cenozoic ascension of mammals

Rise of the Mammals

HHMI Tangled Bank Studios
Premiering 30 October 2019 on PBS at 9pm ET/8pm C; Check local listings.

We live in the Age of Mammals, yet warm-blooded beasts are still overshadowed by dinosaurs. Even when considering the last great shake-up to life’s story, when an enormous asteroid triggered a mass extinction that decimated dinosaurs and gave mammals a shot at terrestrial expansion, we are often more focused on the terrible lizards lost than the furry creatures who set the stage for the Cenozoic. But a new NOVA documentary—“Rise of the Mammals”—seeks to change that and, in the process, offers viewers a window into paleontology beyond bone hunting.

Narrated in soothing tones by actor Keith David, the 1-hour program promises to tell how life surged back after the Cretaceous-Paleogene (K/Pg) mass extinction. The catastrophe, we learn, did not just affect dinosaurs. Flying pterosaurs and seagoing mosasaurs disappeared, as did coil-shelled ammonites and huge clams called rudists, along with mass extinctions of birds, lizards, and mammals. But the mammal-versus-dinosaur competition is the film’s primary focus, with images of tiny, shrew-like insectivores living beneath the feet of dinosaurs providing the background for what follows.

The “Mesozoic mammals as underdogs” trope should be extinct by now. In the past several decades, paleontologists have recognized that mammals thrived during this era, evolving into an impressive array of forms. All were small, fair enough, but so are most of today’s mammal species. To navigate a clear relationship of cause and effect, then, “Rise of the Mammals” emphasizes size. When did mammals start to get big?

An arid field site called Corral Bluffs is offered as the key place to answer this question. How this dot on the map was uncovered is told in a circuitous fashion. We are first introduced to Denver Museum of Nature & Science paleontologist Tyler Lyson and his quest to find fossil beds from the earliest days of the Paleocene, the epoch directly following the Cretaceous.

“Rise of the Mammals” leans heavily on the romance of fieldwork and “Indiana Jones” imagery here, even cribbing a famous sunset shot from “Raiders of the Lost Ark” for full effect. But the key to the story is not a new discovery by Lyson. It is a previous find that was already in the Denver collections.

Paleontology lore often focuses on first authors, field leaders, and museum curators to the exclusion of other workers who make the science possible. To the documentary’s credit, the contribution of Denver museum volunteer Sharon Milito—who made the first critical find at Corral Bluffs, picking up a hard concretion that preserved a Paleocene mammal palate inside—is recognized and underscored by an interview with Milito herself. Lyson happened across this fossil in the Denver collections and, upon visiting the site with colleague Ian Miller, started finding dozens more well-preserved Paleocene fossils.

The film quickly shifts into detective mode. What species were found at the site? How old were they? What was their environment like? Instead of following the standard—and often false—story of how a single discovery changes everything, the program follows various threads to assemble a picture of life in the first million years of the Paleocene.

Although the legacy of storytelling from the “Bone Wars” era of epic fossil hunts is certainly there, the latter half of the film broadens in scope. “Rise of the Mammals” ends up being a short course in modern paleontology, following the story as it goes back and forth between museum and fossil outcrops. The changing face of paleontology is visible, too; the cast of scientists shown and interviewed is much more gender-balanced and diverse than many programs of the past few decades.

The Corral Bluffs fossils are phenomenal, and what they have to tell us about the Paleocene is just starting to drip out into the published record (1), but the ancient ecosystem is only one small part of a global story. Where the film shines—and offers something rare—are the moments when the process of science is allowed to unfold, revealing how experts assemble views of lost worlds. And if nothing else, it is helpful to pry the spotlight out of dinosaurian claws now and then.

References and notes
1. T. R. Lyson et al., Science 10.1126/science.aay2268 (2019).


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About the author

The reviewer is the author of Skeleton Keys: The Secret Life of Bone (Riverhead Books, 2019) and My Beloved Brontosaurus: On the Road with Old Bones, New Science, and Our Favorite Dinosaurs (Scientific American/Farrar, Straus and Giroux, 2014).