So, what's scarier than a slavering, bloodthirsty, 'roided-out pack of gnolls? Anyone? Anyone? Bueller?
A slavering bloodthirsty 'roided-out pack of gnolls riding dinosaurs, that's what!
I think this Pack of Gnolls would be most appropriate in the 4e published Eberron setting, where "behemoths" (aka dinosaurs) are common enough critters that barbarian halflings ride them around the Talenta Plains.
A clan of gnolls that has trained a number of dinosaurs to be mounts and pack animals would be a force to be reckoned with as they travelled across the plains. They would undoubtedly butcher whole tribes of halflings and use their skulls to drink their blood. Nasty stuff like that. Because gnolls are evil, you know.
Come to think of it, this clan of dino-riding gnolls may get its own Island in the Sky...