Temporal range: Late Cretaceous
An artist's restoration of Lythronax
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Genus: Lythronax
Loewen et al., 2013
Species: L. argestes
Binomial name
Lythronax argestes
Loewen et al., 2013

Art impression of Lythronax argestes.png

Lythronax is an extinct genus of tyrannosaurid theropod dinosaur which lived around 80 to 78 million years ago in what is now southern Utah. 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 9 meters (30 feet) in length and weighed 2.5 tonnes (5,500 lbs).

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 and like Tyrannosaurus, it possibly had binocular vision and extremely good senses of smell, hearing and night vision.

Lythronax acristavus by paleoguy-d6z59bv.jpg


Lythronax is known from the most complete tyrannosaurid specimen discovered from southern Laramidia. The careful excavation took nearly a year. This specimen is housed in the collection of Natural History Museum of Utah in Salt Lake City, Utah. The holotype specimen UMNH VP 20200 was recovered in the UMNH VP 1501 locality of the Wahweap Formation at Grand Staircase-Escalante National Monument (GSENM), in Kane County, southern Utah. It was discovered in 2009 by Scott Richardson of Flagstaff, Arizona, and collected from the lower part of the middle member of this formation in terrestrial sediments. The sediments were radioisotopically dated as being 79.6 to 80.75 million years old, meaning that Lythronax is approximately 80 million years old. Based on its stratigraphic position, L. argestes is the oldest tyrannosaurid dinosaur discovered so far.


Its genus name comes from the Greek words ''lythron'' meaning "gore" and ''anax'' meaning "king". The species name is the Greek ἀργεστής, "clearing", used by the ancient poet Homer.


Lythronax was a fairly medium to large tyrannosaur, growing up to 9 metres (30 feet) long from nose to tail and standing over 2 metres tall. It was about the weight of a large crocodile which is around 1-2 tons. It had typical tyrannosauroid features such as the large head, large teeth, small, almost useless arms, the classic s feature commonly found in theropods, forward facing eyes and long heavy tail to balance it while it was running and walking. It probably had a very strong bite which is common with tyrannosaurs so its bite might have been similar in force to the American alligator. It was definitely a carnivore from the shape of its teeth. This particular species would not have been a bone crusher like T. rex but a species that was adept at taking huge chunks out of its prey and waiting for it to die of blood loss like modern day wolves.


Lythronax argestes belongs to the family Tyrannosauridae, a family of large-bodied coelurosaurs, with most genera known from North America and Asia. A detailed phylogenetic analysis, based on 303 cranial and 198 postcranial features, places it and Teratophoneus within Tyrannosaurinae. Lythronax is a sister taxon of a clade consisting of the Maastrichtian taxa Tarbosaurus and Tyrannosaurus and the late Campanian Zhuchengtyrannus. Lythronax was probably not a direct ancestor of Tyrannosaurus, with the two genera sharing a common ancestor that was even older than Lythronax.

In Popular Culture

  • Lythronax made a debut in Fossil Fighters Frontier.