Final answer:
Dinosaurs and pterosaurs became extinct about 65 million years ago at the end of the Cretaceous Period due to a mass extinction event likely caused by a large meteorite impact.
Step-by-step explanation:
Dinosaurs and pterosaurs became extinct during the mass extinction event at the end of the Cretaceous Period. This event, often referred to as the Cretaceous-Tertiary extinction or the K-T extinction, occurred approximately 65 million years ago and led to the demise of not only the dinosaurs but also many other species, including large marine reptiles and pterosaurs.
The primary cause of this extinction event is believed to be the cataclysmic impact of a large meteorite or asteroid near the present-day Yucatán Peninsula. This impact resulted in dramatic changes to the climate and environment, which made the conditions untenable for many of the Earth's species at the time. Birds are the only living descendants of one of the dinosaur clades known as theropods. The post-extinction period allowed mammals to diversify and become the dominant group of land animals.