European settlers of America probably thought they had it hard, but they had no idea of the perils they might have faced. Had things gone differently 10,000 years before, the continent’s predators might have been considerably more fearsome. Much of what we know about the North American animals of the last glacial period comes from the La Brea Tar Pits, but a recent study of those fossils shows we’ve been getting some of these extinct giants wrong.
Located in the heart of Los Angeles, the tar pits provide a spectacular record of more than 600 species that became trapped in the tar over 50,000 years. Dr Larisa DeSantis of Vanderbilt University has been studying the teeth of entombed predators to learn their place in the ecosystems of the day.
Along with the ancestors of gray wolves and coyotes, the pits host larger and more terrifying predators including dire wolves (yes, they were real), saber-toothed cats, and American lions.
Contrary to the message of their chief propagandist, the frequency with which dire wolves were caught in the pits suggests they may not have been smarter than gray wolves. They did, however, have particularly terrifying teeth, and the greatest bite force of any member of the dog family, even when allowing for their size. The American lion, on the other hand, was considerably bigger than its African equivalent.
Their disappearance, and that of the equally dentally fearsome saber-toothed cats, roughly coincided with both the arrival of the first people in North America and the ending of the last ice age. The debate as to whether it was humans or the changing climate that caused the extinction of these giants is among the fiercest in palaeontology.
In Current Biology, DeSantis shows the answers are more likely to vary by species than previously recognized. "Isotopes from the bones previously suggested that the diets of saber-toothed cats and dire wolves overlapped completely, but the isotopes from their teeth give a very different picture," DeSantis said in a statement.
If predators with the same prey went extinct about the same time, it's reasonable to assume they had the same cause. However, DeSantis continued, "The cats, including saber-toothed cats, American lions and cougars, hunted prey that preferred forests, while it was the dire wolves that seemed to specialize on open-country feeders like bison and horses. While there may have been some overlap in what the dominant predators fed on, cats and dogs largely hunted differently from one another." This division held even as climatic conditions shifted.
Prey differentiation increases the chances the extinctions, despite occurring at similar times, had different causes, and rules out the possibility that competition between them was responsible for some species’ demise.
Meanwhile, DeSantis noted, once these large predators disappeared, species like cougars and coyotes that previously fed on smaller prey or scavenged others’ kills were able to expand to fill the new apex niches. Coyotes benefited from the loss of big cats by moving into forest territory as well as consuming larger prey, while the diets of gray wolves and cougars changed less.