Tyrannosaurus Rex or T-Rex (meaning “Tyrant Lizard King”) was one of the largest theropod dinosaur that ever lived. Tyrannosaurus rex was one of the largest terrestrial carnivores of all time, with a weight of 5 tons and a length of about 12-13 meters. However, it did not come close to the size of the earlier Giganotosaurus from South America. But T-Rex had an advantage over Giganotosaurus: its bite. Its jaws alone were 1.2 meters long and 1 meter wide filled with teeth larger than a human hand. The teeth were used to grip prey, breaking bones, puncturing arteries, and rupturing many organs. Tyrannosaurus was unable to chew its food, so it had to swallow food whole, gulping 70 kg (154 lb) of meat at a time. This could be very dangerous because it could potentially choke to death. Tyrannosaurus females were larger than the males and they could lay a maximum of 12 eggs. Tyrannosaurus was the apex predator of North America during the last days of the Late Cretaceous. It preyed on many of the herbivores in the area including Anatotitan, Triceratops, and Torosaurus. It had no predators, but the unborn would be victim to air pollution from nearby volcanoes that prevented their egg shells from forming correctly and nest raiders like Dromaeosaurus and the mammal Didelphodon. The only dinosaurs T-Rex feared were the armored Ankylosaurus and other individuals that belonged to its own genus who were willing to commit cannibalism. Tyrannosaurus was also very aggressive and territorial with, the females being the most aggressive. Females would attract males by emitting loud calls, even calling for weeks for a male. The male respond to these calls by giving the female an animal carcass as a gift to appease her. If she liked the gift, the two would proceed to have a mating period. Afterward, the female Tyrannosaurus would detour the male and would lay her eggs in a mound shaped nest, much like modern crocodilians. During the incubation period, the Tyrannosaurus mother would guard their nests to prevent any nest raiders from eating their eggs, even to the point of denying themselves food just to make sure their nest was protected. But after their young were born, Tyrannosaurus Rex mothers would end their fasting period and would give the juveniles any remains left from their kills. The mother would still protect her chicks even if it killed her in the process. The young were able to to get their mother's attention by chirping. After about 3 months of care, she would either deter them from her care or consume them. It became extinct about 65 million years ago in the Cretaceous-Tertiary mass extinction.