As an ecologist I have spent the past ten years of my professional career tracking apex predators and large herbivores and their effects on whole ecosystems. Abundant research from all sorts of systems demonstrates that when you allow dominant species, such as lions or elephants, to return to ecosystems, they affect many other species in those systems. For example, by toppling small trees, elephants help maintain the rich, open grassland habitat that provides a home for countless species, such as songbirds and insects. By both killing and keeping their prey moving, lions prevent plant-eating animals such as antelopes from damaging shrubs in riparian areas. Ecologists refer to these food web relationships as trophic cascades and to the species that drive these powerful relationships as keystone species. In North America much research has been done on wolf impacts on forest food webs. The wolf’s return to places from which humans had exterminated it has been linked to lush growth of shrubs and trees. However, I am among those scientists who have long suspected that another, more elusive keystone species may be responsible for the trophic cascades we have been witnessing in the northern Rocky Mountains. Still, after putting in thousands of kilometers of track transects in forest ecosystems, I had yet to spot this powerful ecosystem engineer. On a blustery April day in Alberta, my perseverance paid off. The snow had just melted, revealing winter-killed grasses and the carcasses of elk and deer killed by wolves and other predators. My crew and I were pulling a transect deep in an aspen stand, counting elk tracks and scats to determine whether in a system with wolves, elk avoid habitat such as the interior of forests, where it is easier for wolves to kill them. The elk fecal pellets stood out starkly on the forest floor. Among them, cleanly pressed into the forest duff, we spotted some enormous tracks: first one, and then another, and then a half dozen of them in one spot. I noted that the plantigrade, five-toed tracks were those of a large animal. And then it hit me, could it be? I rapidly consulted my field guide to most elusive mammals in the world, which I kept with me at all times in case of such an event as this, and clearly saw that the tracks were definitely those of the creature I had been tracking for years—the ultimate keystone species. The tracks looked fresh—so fresh that we could still smell the animal’s musky scent. I drew my field crew closer and briefed them in whispers. “Be careful, keep your senses as open as possible.” A field technician began to tenaciously pull a transect tape on a north bearing through a seemingly impenetrable tangle of hawthorn. All at once there was an explosion of sound, and out from the hawthorn, impervious to this deciduous shrub’s vicious thorns, burst a tall hairy creature with impossibly large feet—Sasquatchinus grandipedicus, also known as “Bigfoot”—providing incontrovertible evidence that even in science everyone loves a good laugh. As for those trophic cascades, I am still convinced that Bigfoot has had a hand—or a foot—in them, but need more data to fully test this hypothesis.