Final answer:
Allosaurus had physical features such as deadly teeth, long legs, and strong forelimbs that made it an aggressive predator. Bipedal dinosaurs with long necks had long tails for balance and stability during movement.
Step-by-step explanation:
The Allosaurus was indeed designed to be an aggressive predator which can be discerned from some of its physical characteristics. Its deadly set of teeth were perfect for tearing into prey, while its long legs allowed for running and pursuing targets effectively. Furthermore, its strong forelimbs could have been used to grapple and hold onto prey. Combining these traits, it is evident that Allosaurus was a formidable predator of its time, equipped with the necessary adaptations for hunting and subduing other dinosaurs.
Bipedal dinosaurs often had long tails, which counterbalanced their long necks and stabilized them as they moved. Without such tails, maintaining balance, especially while running or making quick turns, would have been much more difficult. These long tails helped to distribute their weight more evenly and allowed for agile and balanced movement. This is why creatures with long necks invariably also had long tails.