The Ginkgo tree is a living fossil. The speed and direction of evolutionary change can vary in a species, allowing some to remain relatively unchanged for long periods of time. Newly found specimens of Ginkgo grew more than a hundred million years ago and are remarkably similar to present-day trees. There are some specimens of Ginkgo in a Chinese monastery garden that are over three thousand years old. Previous fossils have revealed the Ginkgo tree has remained unchanged for over 51 million years, and similar trees were alive and well 170 million years ago, during the Jurassic period. Although there are subtle differences in specimens from the Jurassic period, there is little doubt that this tree is a descendant of forebears that provided food for dinosaurs.