Carnivore dinosaurs were the biggest carnivores to walk on earth. The earliest dinosaur was a carnivore called the Eoraptor, which was probably a scavenger. Carnivore dinosaurs were 5 meter long scavengers to the 40 meter carnivore giants, such as Tyranosaurus Rex. Tyranosaurus Rex was the biggest carnivore to walk on earth and was taller than a double decker bus. Tyranosaurus Rex (see below) may have been a giant carnivore but it was not very smart. Smarter carnivores were often smaller, Velociraptor a small, fast and smart carnivore that hunted in packs was capable of planning an attack. These predators were capable of killing armed dinosaurs like Triceratops. Most carnivore dinosaurs were smarter than herbivore dinosaurs because they needed to plan attacks. Carnivore dinosaurs ate old and sometimes young dinosaurs.