Dinosaurs came in many different shapes and sizes, and they also had a variety of diets. Most dinosaurs ate plants, with the very large dinosaurs eating leaves from the tops of trees and smaller ones eating plants and bushes growing close to the ground. Rocks that contain dinosaur bones also contain fossil pollen and spores that indicate hundreds to thousands of types of plants existed during the Mesozoic Era (70 million to 220 million years ago). Many of these plants had edible leaves, including evergreen conifers (pine trees, redwoods, and their relatives), ferns, mosses, horsetail rushes, cycads, ginkos, and in the latter part of the dinosaur age flowering (fruiting) plants. Some dinosaurs were meat eaters, with most hunting other animals for food and some being scavengers who ate the flesh of dead animals they encountered. The hunters preyed on plant-eating dinosaurs and even on each other. Smaller meat-eating dinosaurs fed on other animals, like insects, lizards, and mammals. Evidence suggests that some dinosaurs hunted in packs, while others lived solitary lives.