Allosaurus was a theropod dinosaur, one of the biggest dinosaurs of the late Jurassic (though not the biggest - that title goes to Saurophaganax or Torvosaurus). JFC had featured in 3 episodes, making it one of its more prominent dinosaurs, on the par with Tyrannosaurus Rex. However, it had a faster, more gracile build than Tyrannosaurus, and a weaker bite, with teeth designed to rip through flesh rather than crush bone, as in case of Tyrannosaurus.
In the episode The Bloodiest Battle (aired August 19, 2008), a trio of allosaurs arrive at a partially dried-out water hole. There, they kill a Ceratosaurus, but a Stegosaurus kills one of the allosaurs, and a bull Camarasaurus, though stuck in the mud, kills the other two.
In the episode Hunter becomes Hunted (aired September 2, 2008), a pair of Ceratosaurs wander into an Allosaurus' territory. The Allosaurus kills first the female Ceratosaurus from an ambush, and then the male Ceratosaurus in a straight-out fight. (Although, since the Allosaurus and the male Ceratosaurus skeletons were found close to each other, maybe the Allosaurus died from wounds recieved during the fight as well.)
These two episodes demonstrate the relative superiority of Allosaurus over Ceratosaurus and other, more primitive hunter dinosaurs.
In the episode Biggest Killers (aired September 9, 2008) clips of Allosaurus were shown to demonstate its power and hunting prowess. Since this episode was more of a clip show, the Allosaurus killed no dinosaur and was killed by none.
Comparison of Allosaurus and Tyrannosaurus from official JFC site (now defunct).