Final answer:
The key evolutionary novelty of the Allosauridae family is their serrated teeth, which were adapted for tearing flesh, making them effective carnivorous predators.
Step-by-step explanation:
The key evolutionary novelties of the Allosauridae, a family of large theropod dinosaurs, included characteristics that were adapted for their carnivorous lifestyle. Among the distinctive features they possessed, one notable trait is their serrated teeth, which were adapted for slicing through flesh. This feature allowed them to be effective predators during their time.
It's important to note that although they had clawed hands, which were also crucial for their hunting habits, the mention of serrated teeth is a direct novelty that can be singled out as a defining characteristic. Other features, such as skull shape and jaw configuration, played significant roles in the evolution of various dinosaur clades and contributed to their success as dominant predators during the Mesozoic era.