| Named By: | M. A. Loewen, R. B. Irmis, J. J. W. Sertich, P. J. Currie & S. D. Sampson in 2013 |
| Time Period: | Late Cretaceous, 80 Ma |
| Location: | USA, Utah - Kaiparowits Formation |
| Size: | Holotype estimated to be around 7.3 meters long. Speculated to have possibly attained lengths of 8 meters |
| Diet: | Carnivore |
| Fossil(s): | Partial skull and post cranial remains of an adult including the tibia, fibula, pubis metatarsal II and IV (UMNH VP 20200) |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Coelurosauria | Theropoda | Tyrannosauroidea | Tyrannosauridae | Tyrannosaurinae | |
Lythronax is an extinct genus of tyrannosaurid theropod dinosaur that lived around 80.6 to 79.9 million years ago in what is now southern Utah, USA. The generic name is derived from the Greek words lythron meaning "gore" and anax meaning "king". Lythronax was a large sized, moderately-built, ground-dwelling, bipedal carnivore that could grow up to an estimated 8 m (26.2 ft) in length and weighed 2.5 tonnes (5,500 lb).
L. argestes is the oldest known tyrannosaurid, based on its stratigraphic position. It is known from a specimen thought to be from a single adult that consists of a mostly complete skull, both pubic bones, a tibia, fibula, and metatarsal II and IV from the left hindlimb, as well as an assortment of other bones. Its skull anatomy indicates that, like Tyrannosaurus, Lythronax had both eyes facing the front, giving it depth perception.