Extinction
The end of the ice age where ice retreated to reveal grasslands, the summers became more extreme, and parts of North America dried out. The cause of their extinction was most likely climate change, terrain change and hunting by humans. Their prey became extinct, so they lost a primary source of food. Since they could not catch quick and agile prey, starvation was another cause. The ice sheets also revealed more grasslands at the end of the ice age that caused summers to get hotter and longer.