Lythronax (LYE-thro-nax) is a genus of Tyrannosaurus dinosaurs that lived in North America in the late Cretaceous period about 806--79.9 million years ago. The only known specimen was found in 2009 in the Wahweap group of the Grand Staircase-Escalante National Monument in Utah. It is composed of partial skulls and bones. In 2013, it became the basis for a new genus and species of Lythronax argestes; the common name Lythronax means "king of blood", and the specific name argestes is derived from the name of the Greek poet Homer for the southwest wind, referring to the geographical origin of the specimen in North America.
The size of Lythronax is estimated to be between 5 to 8 m (16 to 26 feet) in length and 0.5 to 2.5 tons (1,100 to 5,500 pounds) in weight. It is a huge tyrannosaurus. As a member of this group, its forelimbs are very small, with only two fingers, its hind limbs are strong, and its skull is very strong. The posterior part of Lythronax's skull appears to be very broad, with the eye sockets facing forward similar to Tyrannosaurus. Lythronax has 11 alveoli in the maxilla of the upper jaw; most Tyrannosaurus has more. The front teeth are the largest, with the longest being nearly 13 cm (5 inches) long. Other details of the skull and bones that distinguish Lythronax from other Tyrannosaurus families include the S-shaped outer edge of the maxilla and the astragalus protrusion on the ankle, which expands further upwards compared to its relatives.
The orthomodel model was found in the middle of the Wahweap Formation and can be traced back to the Campanian of the Cretaceous. Therefore, Lythronax is the oldest known member of the Tyrannosaurus family, and it is considered to be more basic than Tyrannosaurus. Due to its age, Lythronax is very important for understanding the evolutionary origin of Tyrannosaurus, including the development of their anatomical specialties. Lythronax's forward-facing eyes give it depth perception, which can be useful when chasing or ambushing predators.