Ankylosaurus, meaning “fused lizard”, is a genus of dinosaur of the Late Cretaceous Period from western North America. This armored dinosaur is known by only partial discoveries. The only species known is A. magniventris. Ankylosaurus was named by Barnum Brown in 1908. He also led the expedition that discovered the specimen in Hell Creek Formation in 1906. He discovered another specimen in 1910 in Alberta from the Scollard Formation. Three of his discoveries from this genus are housed at the American Museum of Natural History in NYC. Charles M. Sternberg discovered the largest known skull of this genus in 1947, which is housed at the Canadian Museum of Nature. Numerous other fragments have been found throughout the years.

Compared to modern land mammals, Ankylosaurus was quite large. It has an estimated length of 30 feet, however, some scientists suggest it was much smaller at an estimated 20.5 feet. It stood about 5.5 feet high at the hip. Its weight may have toppled the scales at nearly 13,000 pounds. Its body was low to the ground and rather wide. It was a quadrupedal, with longer hind limbs than forelimbs. Although no foot bones were ever found, it is believed it had five toes on each foot, like other ankylosaurid dinosaurs. The skull was low and triangular. It was wider than it was long. The largest known skull measures 29 inches wide and 25 inches long. This herbivore had small, leaf-shaped teeth suited for cropping vegetation.

The prominent feature of the Ankylosaurus was its armor. It consisted of massive knobs and plates of bone embedded in the skin. These knobs and plates are known as scutes. These scutes were most likely overlain with a tough layer of keratin. The scutes ranged greatly in size, from wide, flat plates to small, round knobs. The plates were aligned horizontally in rows down the neck, back, and hips. The small knobs protected the areas in between the plates. The limbs and tail may have been armored with smaller scutes. The top of the skull was protected by tough, rounded scales, and four large horns projected outwards from the rear corners of the skull.

Its tail club was also composed of several large scutes that were fused to the last few tail vertebrae. The club was heavy and supported by the last seven tail vertebrae, which interlocked to form a stiff rod at the base of the club. The tail was an active defensive weapon and was very powerful. A swing of the tail could be enough to break the bones of a predator.

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