From Academic Kids
Conservation status: Fossil
Ankylosaurus was the last, largest, 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 exposed. It also had a great club-like tail that could be used for defense against predators. Ankylosaurus was about the size of an elephant, but had a low-slung, very wide body. It is one of the most heavily armored dinosaurs to have ever been found.
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) tall. Its legs were short, with the rear legs longer than the forelegs. It had five toes on each foot. The flat, triangular skull was thick, meaning 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. The bone was probably overlain by a tough, horny layer of keratin. Some of these plates were developed in short spikes, others fused onto the skull forming hornlets, and a few fused to the end of the tail to form the massive tail club. The tail was muscular, so it probably made an effective defensive weapon.
Ankylosaurus existed between 65 and 70 million years ago, in the Maastrichian age of the Late Cretaceous period, and was one of the last dinosaurs before they were wiped out by the Cretaceous-Tertiary extinction event.
Even giant carnivores of the Maastrichian, like Tyrannosaurus, Deinonychus, and Tarbosaurus, probably could not break through ankylosaur armor. It is believed they would lie flat on the ground, hiding their soft stomach from attackers. Like a porcupine, they were only vulnerable when flipped over, which was made more difficult by the row of short spikes running down their sides.
Classification and history
The only species in the genera, Ankylosaurus magniventris, was named by Barnum Brown in 1908. Fossil remains have been found in Alberta, Canada, as well as in Wyoming and Montana in the United States. Euoplocephalus was originally 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 trackway of an ankylosaur was found in Sucre, Bolivia in 1996, which showed that the massive dinosaur could move fairly quickly.
The name Ankylosaurus is derived from the Greek agkylos, meaning "bent" or "crooked", and sauros, meaning "lizard". This refers to the way the bony plates on its back have fused with the thick skin, and the way many of the internal supporting structures like the backbone (vertebrae) and ribs have also fused together.