The main reason why the evolutionary history of early amphibians in the late Paleozoic is better known than that of early birds in the Mesozoic is due to differences in the fossil record. Fossils of early amphibians are more abundant and better preserved in the rock record than fossils of early birds. This is partly because the early amphibians were terrestrial and had a higher chance of being preserved in sedimentary rocks, whereas early birds were more likely to live in trees and other environments where their remains were less likely to be preserved. Additionally, the early amphibians were larger and had thicker bones, which are more likely to fossilize than the smaller, lighter bones of early birds. Therefore, while there is still much to learn about the evolutionary history of both groups, the fossil record provides more information about the early amphibians than the early birds.