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Ankylosaurus

Ankylosaurus is one of the most recognizable dinosaurs and also one of the best known to the general public because of its unique appearance: often nicknamed the Cretaceous sherman tank, this beast had a thick, almost impenetrable armor of osteoderms that protected its head, its neck, its back and even its tail. The only part of the body of this animal that was vulnerable to predator bites was the underside of its belly, soft and popular with tyrannosaurs. The Ankylosaurus shield was made of deeply embedded bone plates covered with a thick layer of keratin, a protein contained in human hair, bird's beaks and rhinoceros horns.

Shielding armor

Although the Ankylosaurus bone shell already offered it strong protection against theropod attacks, the dinosaur's hard tail was also adorned with a huge, heavy club that it could swing like a demolition ball at a reasonable speed to smash the bones of raptors and tyrannosaurs who wanted to feed on it. With an approximate weight of three to four tons and a very low center of gravity, ankylosaurs that reached adulthood were virtually immune from predator attacks. It was almost impossible, even for a desperately hungry tyrannosaurus, to tip a mature Ankylosaurus in order to chew on its tender belly. The higher Cretaceous theropods preferred to prey on more vulnerable prey such as juveniles or even newborns.

Thyreophoran

Ankylosaurus belongs to a group of dinosaurs named thyreophorans, a family of quadruped ornithischian herbivores characterized by a battleship-backed bony plates, spades and spurs. This grouping also includes stegosaurs whose armor was in the form of a double row of plates and bony pikes projecting upwards.

Ankylosaurus or Dynamosaurus

The name Ankylosaurus, or "fused lizard," was granted in 1908 by the famous paleontologist and fur coat enthusiast Barnum Brown, two years after unearthing the holotype specimen in the Hell Creek formation in Montana. This name was in the same sense as the medical term "ankylosis" which refers to the rigidity and immobility produced by the fusion of several bones in the body. Brown eventually found many other remains including several pieces of fossilized armor first attributed to a dinosaur he named Dynamosaurus. This name however later disappeared from the paleontological archives and was replaced by Ankylosaurus.

Most of the Ankylosaurus bones have been discovered in Montana, Wyoming and also in the Canadian province of Alberta. However, it is now known that ankylosaurs have occupied a much larger area than just the American West, as remains of other less known species of ankylosaurs have been found on all continents except Africa. The similarity of their morphologies is undoubtedly attributable to a phenomenon called convergent evolution.

A peanut in the noggin

Sadly and as imposingly as it was, Ankylosaurus proudly honored thyreophorans and competed with Stegosaurus for the title of the most dim-witted animal of the Mesozoic era. Its brain was barely bigger than a walnut and only allowed the most rudimentary reflexes.

Close relative of Euoplocephalus

Ankylosaurus was closely related to Euoplocephalus, although the latter is represented by a much larger number of fossils. The remains of this smaller ankylosaur abound so much that we know that even its eyelids were covered by bony plates. Like its close relative, Ankylosaurus had a complex system of channels inside its skull. It is also possible that they were used to heat the air, thus recovering water from the exhaled air or improving the sense of smell. It is also possible that they have been used as a resonance chamber, helping the animal to make distress calls or during mating.

Ankylosaurus would have survived the initial comet impact

Assuming that Ankylosaurus possessed a cold-blooded metabolism as many researchers believe combined with its impenetrable armor, one might think that this dinosaur may have managed to survive longer after the initial comet impact on the Yucatan Peninsula. The remaining populations would then slowly succumb to the disappearance of the trees and ferns to which they were so accustomed after vast clouds of dust completely encircled the Earth.

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