Ankylosaurus is a genus of armored dinosaur. Possibly the largest-known ankylosaurid, Ankylosaurus is estimated to have been between 6 and 8 metres (19.7 and 26.2 ft) long and to have weighed between 4.8 and 8 tonnes (5.3 and 8.8 short tons). It was quadrupedal, with a broad, robust body. It had a wide, low skull, with two horns pointing backward from the back of the head, and two horns below these that pointed backward and down. Unlike other ankylosaurs, its nostrils faced sideways rather than towards the front. The front part of the jaws was covered in a beak, with rows of small, leaf-shaped teeth farther behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name.