How they got there, transforming from four-legged, landlubbing also-rans, patrolling Pakistani riverbanks, to the globe-spanning marine colossus of earth’s history is the sort of question that gets people to pursue Ph.D.’s in paleontology in the first place.

“Among mammals, whales really stand out to me for having to have met the most obstacles in their evolution,” says Marx. “They’re really a poster child of evolution.”

The evolution of whales spans whole ages and unfamiliar worlds. It draws from an oeuvre that includes, not only paleontology, but paleoclimatology, oceanography, geology and paleoecology as well. To get a foothold on this dizzying sweep, UC Berkeley Ph.D. candidate Larry Taylor has decided to probe something smaller. Not the whales themselves, but the barnacles that cling to the animals—hitching rides around the planet. As Taylor realized, oxygen isotopes in barnacle shells act as a chemical passport of a whale’s travels, filled with stamps from the world’s various oceans. And humpback-whale barnacles go back millions of years in the fossil record. Taylor hopes to find ancient whale journeys coded in these fossil shells—journeys that could illuminate the evolution of whales and, perhaps even, why some got so preposterously large.

Starting about three million years ago, after a long decline from the high-CO2 greenhouse of the dinosaurs, the earth descended into a waxing and waning low-CO2 ice age—one that continues to this day (albeit precariously). In this ongoing ice age, the planet has swung back and forth between more wintry climes when there was a half-mile of ice crushing Boston and sea levels were 400 feet lower—to warm, but brief, interglacials like today, when the ice sheets temporarily retreat to the poles. And back and forth and back and forth and back again, as the northern hemisphere wobbles in and out of the sunshine. If Taylor’s barnacle data showed ancient whales changing their behavior in response to these climate changes, it might go a long way in explaining why baleen whales in particular (those bristle-mouthed whales that gulp plankton by the ton) have become globe-traveling giants, capable of going months without food—and dwarfing every other animal in the planet’s history.

“Essentially no one knows anything about whale migration in the prehistoric past,” says Taylor. “But the idea would be that as climate got more unstable in the last several million years—and we went through glacial maximums and minimums—the productive zones of the oceans would have been shifting around a lot, and these huge animals could quickly adapt their behavior to find these productive zones of the ocean. Evolution might have favored these really large animals that could migrate huge distances and survive off an enormous fat store.”

It’s an intuitive idea. But it’s long been just that—an idea. This is where Taylor’s humpback barnacles come in. The unassuming shells effectively act as a black box for whale journeys of the distant past.