The Animantarx was an approximately 3-metre-long dinosaur with bone plate armour. The Animantarx was an approximately 3-metre-long dinosaur with bone plate armour. Only one skeleton of the dinosaur has ever been found, so we dont really know so much about it. It lived during the Upper Cretaceous period, at the time of Argentinosaurus and Giganotosaurus, and fed on plants. Fun fact The thick armour gave the Animantarx its name. Its name contains the Latin word arx, meaning fortress.