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Ankylosaurus

Ankylosaurus was the last, main, and most famous of the armored dinosaurs known as the Ankylosaurians. Its back and sides were covered with a stiff shell of armor, but its underbelly was uncovered. It also had a great club-like tail that might be used for defense against predators. Ankylosaurus was about the size of an elephant, but had a low-slung, extremely wide body. It is one of the most heavily armored dinosaurs to have ever been found.

Description Ankylosaurs weighed up to 4.5 metric tons (5 tons), and were about 10 meters (30 feet) long. While they were 1.8 meters (6 feet) wide, there were only 1.2 meters (4 feet) high. Its legs were short, with the stern legs longer than the forelegs. It had five toes on each foot. The flat, triangular skull was thick, significance the brain was quite small. Massive knobs and plates of bone, known as osteoderms, were embedded in the skin of an ankylosaur, as in crocodiles, armadillos, and some lizards. A tough, thorny layer of keratin probably overlay the bone.

Some of these plates were urbanized in short spikes, others fused onto the skull forming hornlets, and a few fused to the end of the tail to form the enormous tail club. The tail was muscular, so it probably made an effective defensive weapon.

Environment
Ankylosaurus existed between 65 and 70 million years ago, in the Maastrichian age of the Late Cretaceous era, and was one of the last dinosaurs before they were wiped out by the Cretaceous-Tertiary death event.

They were plant-eaters (herbivores). Being stiff and low-slung, they must have grazed on low-lying plants.

Even giant carnivores of the Maastrichian, like Tyrannosaurus, Deinonychus, and Tarbosaurus, almost certainly could not break through ankylosaur armor. It is supposed they would lie flat on the ground, hiding their soft abdomen from attackers. Like a porcupine, they were only susceptible when flipped over, which was made more difficult by the row of short spikes running down their sides.

Classification and history
Barnum Brown named the only species in the genera, Ankylosaurus magniventris, in 1908. Fossil remains have been found in Alberta, Canada, as well as in Wyoming and Montana in the United States. Euoplocephalus was initially believed to be an ankylosaur, but it now has its own genera.

The remains are fairly complete, including a couple skulls and the signature tail. A track way of an ankylosaur was found in Sucre, Bolivia in 1996, which showed that the massive dinosaur could move quite quickly.

Etymology
The name Ankylosaurus is resulting from the Greek agkylos, meaning "bent" or "crooked", and sauros, meaning "lizard". This refers to the way the bony plates on its back have complex with the thick skin, and the way many of the internal supporting structures like the backbone (vertebrae) and ribs have also fused together.