Tyrannosaurus

MEANING: Tyrant lizard

PERIOD: Late Cretaceous

CONTINENT: North America

Tyrannosaurus is a large North American theropod, and the last known tyrannosaurid living before the end-Cretaceous extinction event. One of the largest land carnivores of all time, Tyrannosaurus grew to about 12 m long, weighing up to 9 t. The massive skull bones were fused and pneumatized, allowing for an extremely powerful bite. The tip of the snout was U-shaped, which increased the amount of tissue a tyrannosaur could bite off its prey. The skull of Tyrannosaurus was wide at the rear but had a narrow snout, allowing unusually good binocular vision. It was likely both an active predator and a scavenger, but the specifics of its feeding behavior and lifestyle are still debated.

Tyrannosaurus is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.

Tyrannosaurus is a tyrannosaur. Tyrannosauroidea is a group of theropod dinosaurs known for often being the largest predators in their ecosystems, at the top of the food chain. They evolved throughout the Cretaceous, starting as relatively small predators before giving rise to some of the largest carnivores to ever walk the Earth. Early tyrannosaurs from the Jurassic and Early Cretaceous were generally small-bodied and built for speed, with long arms and three-fingered hands. Some of these early forms are known to have been feathered. Early tyrannosaurs lived alongside larger predatory dinosaurs like carcharodontosaurs, which dominated apex predator niches in many regions.

As the Cretaceous progressed, tyrannosaurs gradually increased in size, with later forms evolving more robust skulls, stronger bite forces, and reduced arms. By the Late Cretaceous, the most derived members of the group had become massive apex predators with thick, deep skulls specialized for crushing bone. These tyrannosaurids had only two functional fingers on each hand, a trait that distinguished them from earlier relatives. By this time, tyrannosaurs had largely replaced other large theropods in North America and Asia, cementing their role as dominant predators by the end of the Mesozoic.