Change in climate
In the fossil records of the Montana Badlands there is a black marker of coal and some excellently preserved fossilized tree stumps. Below this marker was the last of the cycad and tree fern forest, but the tree stumps represent the coniferous redwoods (Sequoia). These later plants prefer a much cooler climate than the cycads and tree ferns. Although a large body can retain heat more efficiently, if it becomes cooled, it becomes increasingly more difficult to gain heat. In contrast very small animals can find micro-habitats that reduce exposure to unfavourable conditions and can more quickly warm their bodies up during favourable conditions. Aquatic animals also have a greater buffer against temperature since water maintains heat more efficiently than land. Consequently the three main types of reptiles that endured the late Cretaceous extinction were lizards, tortoises and turtles and crocodiles, all either small-sized or aquatic animals.