Final answer:
The provided details discuss therapsids, a group that evolved mammalian traits and survived into the Triassic period by being small, arboreal, and nocturnal. This information, however, does not address the question about theropods, a separate group from dinosaurs known for their distinct dental characteristics.
Step-by-step explanation:
The student's question deals with a specific characteristic of theropods, a group of prehistoric reptiles closely related to dinosaurs. However, the information provided relates to therapsids, which were a separate group of early amniotes that eventually gave rise to mammals. The passage does not directly answer the student's question about theropods, but rather describes the evolution and characteristics of therapsids, mentioning their time of existence around 260 million years ago, their changes in appearance resembling mammals, as well as their adaptation for becoming nocturnal insect eaters in the Triassic period.
It is important to note that although therapsids and theropods may sound similar, they represent distinct groups within the evolutionary history. Therapsids are not the theropods that the student asked about; the theropods are a different group known for being bipedal carnivores like the Tyrannosaurus rex, and are not directly related to the characteristics described of therapsids.