Quadrusaurus ileri

Name: Quadrusaurus ileri
Meaning: Ileri's quadruped lizard

Clade: Carnosauria
Family: Novasauridae

Length: 30 - 36 foot
Height: 12 - 14 foot
Weight: 6 - 8 tonnes
Fossil remains: Mostly complete skull and majority of skeleton
Age: Mid to late Cretaceous. Lower North America

The family, Novasauridae, represents an important discovery in carnosaur evolution. By the early and mid Cretaceous, the 'classic' carnosaurs were increasingly being restricted in habitat by changing conditions. The narrow head, teeth and longer arms of these carnosaurs signaled them out as 'specialized' sauropod hunters, and with the changing fauna towards smaller hardosaurs and ceratopsians, as well as competition from the emerging tyrannosaurs across North America and Asia, forced the carnosaurs to retreat. The classic carnosaur body plan survived, and even thrived, in South America and Africa where sauropods still remained (As evidenced by Giganotosaurus and Carcharodontosaurus). Novasauridae however hung on in the northern hemisphere, showing previously unknown adaptations in response to the new prey species.

The discovery of Quadrusaurus brings to light these new adaptions. The skull of this predator is still relatively narrow, as in previous carnosaurs before it, but it is larger in relation to the body than say that of Allosaurus. Slight broadening at the rear of the skull has opened up larger sites for muscle attachment, and has even increased the range of binocular vision over that of 'traditional' carnosaurs. Changes in dentition can be seen, with the teeth at the front of the jaw becoming 'rounder' in cross section. This adaption is seen in tyrannosaurs, and is suspected to show a transition in Novasauridae from slashing teeth to puncturing teeth, ideal for holding onto 'smaller' prey. The neck is shorter, but more heavily muscled.

The body of Quadrusaurus shows an interesting adaption to the newer skull size and shape. In tyrannosaurs, the increasing size and power of the skull as they evolved was offset by a reduction in size and weight of the arms, still permitting them to walk bipedal. In Novasauridae, and taken to the extreme in Quadrusaurus, the arms have become longer and more powerful, forcing the theropod to adopt a semi-permanent quadrupedal gait. Muscle attachment sites on the shoulder and humerus are large. And the bones of the wrist have changed, rotating the hand. Quadrusaurus was a knuckle-walker, able to support it's weight in much the same way as a giant ground sloth would have. The tail is long, contributing to much of the theropod's length.

One other interesting thing found within Novasauridae is the presence of scutes, a feature usually associated with ceratosaurs and abelisaurs, not with Carnosauria. Quadrusaurus possessed one prominent row of scutes running down the spine. These scutes would not provide the theropod with any protection from prey or rivals, and so it is assumed they may have played some role in display.

Quadrusaurus lived at a time where the herbivorous populations were undergoing a significant change. Sauropods still remained, but they were slowly being replaced by ceratopsians and hadrosaurs. It is thought that by the time Quadrusaurus ileri had evolved, Novasauridae had almost fully transitioned from hunting 'big' to 'small' prey. There is still debate on how Quadrusaurus fed. Current consensus points to it being an ambush hunter. The long powerful arms, were tipped with large claws, perfect for hooking the limbs of it's prey and tripping it up. This would give the theropod time to close in and bite, using it's puncturing teeth and strong skull to grab hold of the victim. Large neck muscles would then allow Quadrusaurus to shake and wrestle with it's prey, tearing out large chucks of flesh and breaking the prey's neck/back.