During the last Ice Age, when the ancestors of all Native Americans first migrated into North America from Asia, giant mammals and flightless birds of prey flourished in most ecological niches in both American continents. Some of these creatures appear to be super-sized versions of modern mammals, such as the wooly mammoths and rhinos, American cave lions, giant beavers, cave bears, and saber-toothed cats. This megafauna was prevalent throughout Eurasia, South America, and Australia at the Pleistocene epoch, which last between 2.6 million years to 11,700 years ago. Paleontologists have questioned about why and how these creatures had become so large, and a recent finding at the La Brea tar pits in Los Angeles may yield some clues. Based on the recent evidence of fossils of Ice Age giant predators, paleontologists think that climate change may have guided the evolution of the megafauna. By studying the connection between climate change and these predators, they could predict how modern animals may respond to the current climate change.
A study was recently published in the Journal of Evolutionary Biology that described and compared the different sizes of saber-toothed cats’ jaws from different excavation sites. According to Julie Meachen of Des Moines University, who lead the research on saber-toothed cats, the fossils they found indicated that cats living after the last Ice Age were larger and were adapted to killing larger prey. This is evidence that showed “a clear correlation between climate and shape.” The study stated that rapid warming events at the of the last Ice Age “appear to be correlated with larger derived morphologies” of the megafauna, while cooler and more stable climates correlate with more slender physiques.
Another research team from the Page Museum that examined fossils of dire wolves, which were similar to modern gray wolves, found that they also shared a similar pattern. Robin O’Keefe, who is the lead author of the dire wolf study that was published in Palaeontologia Electronica, compared different wolf fossils from different layers of the fossil record. The more recent skulls exhibited larger size than older fossils.
Scientists are still uncertain how or why these giant mammals became extinct about 10,000 years ago. Although there are evidence suggesting that humans may have hunted the giant herbivores to extinction, which in turn decreased the giant predators’ population, climate change may contribute to the megafauna’s wipeout.
At the end of the last Ice Age, climate change fluctuated with periods of rapid cooling and warming that guided the evolution of the megafauna, particularly the giant predators. Back then, the flora was much more diverse than it is today. Herds of wooly mammoths, wooly rhinos, giant bisons, and North American horses grazed on the protein-rich forbs, a type of herbaceous flowering plant, that spread throughout much of the continent like a shag carpet. When the climate got colder and the ice sheets and glaciers advanced further south, most of the forbs became less diverse and most of the populations died out. This brought bad news for the giant grazers, and hundreds of thousands of them may have died out over thousands of years. With less prey to eat, the predator populations also dropped. These nutritious forbs never fully recovered to their former abundance after the peak of the last Ice Age, which may have contributed a large percentage of the extinctions of many species, including mammoths, Irish elks, and horses.
So why should people care about climate change, evolution, and ancient extinctions? By studying the change patterns in the last million years or so, scientists can predict what may happen to the modern ecosystem with the current climate change. As the climate got warmer after the last Ice Age, grass species and woody plants took over the ecosystems that the forbs used to inhabit. This gave rise to different species of animals that adapted to this new environment. The current change would place environmental stress upon plants and animals that may likely triggers a change or two to adapt to their surroundings. Evolution among modern prey and predators may guide them to evolve in a very similar way that their ancient ancestors had responded to the climate change in the last Ice Age.
By Nick Ng