The ankylosaurus became extinct with the other great dinosaurs during the Cretaceous-Paleogene extinction event that occurred about 66 million years ago. While some questions remain about what caused this extinction, geologic evidence suggests that at least one massive asteroid or comet impacted the Earth, sending shock waves through the atmosphere and drastically changing the climate.
The earliest ankylosaurus fossils date back 66.5 million years, marking this species as one of the last to appear before the mass extinction that wiped out the dinosaurs. Most of the existing fossils of this species have been found in Wyoming, Montana and Canada.
The Alvarez hypothesis is the leading explanation for what wiped out the dinosaurs. It posits that a very large asteroid struck the Earth, setting off events that caused the dinosaurs' ecosystem to collapse. The discovery of a massive crater off the Yucatan peninsula and the presence of iridium in worldwide sediment around the time of this event offer strong evidence in favor of the hypothesis. Iridium is an extremely rare metal only found in asteroids, and its presence at the end of the Cretaceous Period suggests at least one massive rock crashed to Earth at that time. However, the Yucatan crater is not the only large crater from this time period, leading some paleontologists and geologists to suggest that not one but a series of impacts devastated the Earth and killed off the dinosaurs.