Gigantohetrus

Gigantohetrus is an extinct dinosaur and was one of the largest and the last of the Heterodontosaurid dinosaurs, living in what is now Argentina from the Early Cretaceous 105 million years ago to the Late Cretaceous 66 million years ago, being alive as a species for 39 million years. They were about the size of an Edmontosaurus of Late Cretaceous North America. Gigantohetrus was most likely completely herbivorous as their teeth suggests, and since their fossils were found close to other Gigantohetrus skeletons, it is likely that they were herd animals that lived in large herds. They also had thumb spikes as well as fifth grasping finger, which was once thought to be restricted only to Iguanodonts, with its thumb spike probably used to fight back against predators and/or possibly to fight other males to see who would become the leader of the herd, as some scientists suggested. They had large bodies and thick legs, suggesting that they were probably mostly quadrupedal animals, only to stand on back legs to look out for predators or when they were about to attack or fight back using their thumb spikes. The brain case is unusually large compared to many other kinds of Heterodontosaurids, comparable to that of modern day horses, so it is possible that Gigantohetrus was about as intelligent as domestic horses. It is unknown on why the Gigantohetrus became extinct in the Late Cretaceous period.