ABSTRACT
The Pleistocene (the ice ages) was a time of advancing and retreating glacial episodes and the concomitant lowering and rising of sea levels. It was remarkable as well for the many large mammals that existed in North and South America, and that become extinct at or near the end of the last glacial period around 12,000 years ago.
The Southern California region alone was home to, among other species, several kinds of elephants, ground sloths, different horses, tapirs, camels, as well as formidable predators like cheetahs, saber-toothed cats, and the American race of the African lion. North America lost 34 genera of large (> 100 lbs/45 kg) mammals and 3 genera of small ones. South America lost 51 genera.
There were no meteor strikes at the end of the Pleistocene or any other disaster of global proportions. What could have caused the sudden disappearance of a staggering number of large and medium-sized mammals 12,000 years ago leaving smaller vertebrates essentially unaffected? Some paleontologists have long favored a climate-based explanation. Yet warm–cold cycles were a consistent pattern over the 1.8 million years of the Pleistocene as normal background extinction took place.
An alternative explanation is that the large mammals were ill prepared for the ecological challenges of human arrival into North and then South America. Predation was likely the most important contributor. From a global perspective (continents and oceanic islands), the striking feature of extinction in near time (the last 40,000 years) is the episodic, sequential coincidence of vanishing species with the arrival of humans to places where they had never been.
