Final answer:
Derived characters diagnostic of Theropoda include hollow bones, a three-fingered hand, the presence of a furcula (wishbone), and feathers or feather-like structures.
Step-by-step explanation:
Derived characters, or apomorphies, diagnostic of Theropoda include several specific traits that distinguish them from other groups. Theropods are a group of bipedal saurischian dinosaurs that are ancestral to birds and include well-known species like Tyrannosaurus and Velociraptor. Some of the diagnostic derived characters of theropods are:
- Hollow bones, which made them lighter and possibly helped them in active predation or flight (in the case of birds).
- A three-fingered hand, where the third finger is reduced.
- The presence of a furcula, or wishbone, which is also found in birds.
- Feathers or feather-like structures, which have been found in several theropod fossils, indicating their presence across the group.
These apomorphies help scientists to classify theropods within the larger dinosaur clade and trace the evolution of traits leading to modern birds.