The fossil record reveals that modern reptiles are not just descendants of ancient reptile lineages but are also closely related to birds, making them part of a broader group called amniotes. While most reptile groups flourished during the Mesozoic era, only a few lineages survived the mass extinction events, leading to the diverse forms we see today. Key subtopics include the connection to birds, which are technically avian reptiles, and the surviving ancient lineages such as crocodilians and tuataras.