Lythronax was found in terrestrial sedimentary rocks belonging to the lower part of the middle member of the Wahweap Formation.
These rocks have been radioisotopically dated to 79.6 to 80.75 million years ago, meaning that Lythronax lived approximately 80 million years ago, and thus dates to the Campanian.
The overall Wahweap Formation has been radiometrically dated as being between 81 and 76 million years old.
During the time Lythronax lived, the Western Interior Seaway was at its widest extent, almost completely isolating southern Laramidia from the rest of North America.
The area where dinosaurs existed included lakes, floodplains, and rivers, which flowed east.
The Wahweap Formation is part of the Grand Staircase region, an immense sequence of sedimentary rock layers that stretch south from Bryce Canyon National Park through Zion National Park and into the Grand Canyon.
Among other lines of evidence, the presence of rapidly deposited sediments suggests a wet, seasonal climate.

Lythronax was likely the largest predator of its ecosystem.
It shared its paleoenvironment with other dinosaurs, such as the hadrosaurs Acristavus and Adelolophus, the ceratopsian Diabloceratops, and unnamed ankylosaurs and pachycephalosaurs.
Vertebrates present in the Wahweap Formation at the time included freshwater fish, bowfins, abundant rays and sharks, turtles such as Compsemys, crocodilians, and lungfish.
Numerous mammals lived in this region, which included several genera of multituberculates, cladotherians, marsupials, and placental insectivores.
The mammals were more primitive than those that lived in the younger Kaiparowits Formation.
Trace fossils are relatively abundant in the Wahweap Formation, and suggest the presence of crocodylomorphs, as well as ornithischian and theropod dinosaurs.
Evidence of invertebrate activity in this formation ranged from fossilized insect burrows in petrified logs to fossils of mollusks, large crabs, and a wide diversity of gastropods and ostracods.
Lythronax was found in terrestrial sedimentary rocks belonging to the lower part of the middle member of the Wahweap Formation. These rocks have been radioisotopically dated to 79.6 to 80.75 million years ago, meaning that Lythronax lived approximately 80 million years ago, and thus dates to the Campanian. The overall Wahweap Formation has been radiometrically dated as being between 81 and 76 million years old. During the time Lythronax lived, the Western Interior Seaway was at its widest extent, almost completely isolating southern Laramidia from the rest of North America. The area where dinosaurs existed included lakes, floodplains, and rivers, which flowed east. The Wahweap Formation is part of the Grand Staircase region, an immense sequence of sedimentary rock layers that stretch south from Bryce Canyon National Park through Zion National Park and into the Grand Canyon. Among other lines of evidence, the presence of rapidly deposited sediments suggests a wet, seasonal climate.
Lythronax was likely the largest predator of its ecosystem. It shared its paleoenvironment with other dinosaurs, such as the hadrosaurs Acristavus and Adelolophus, the ceratopsian Diabloceratops, and unnamed ankylosaurs and pachycephalosaurs. Vertebrates present in the Wahweap Formation at the time included freshwater fish, bowfins, abundant rays and sharks, turtles such as Compsemys, crocodilians, and lungfish. Numerous mammals lived in this region, which included several genera of multituberculates, cladotherians, marsupials, and placental insectivores. The mammals were more primitive than those that lived in the younger Kaiparowits Formation. Trace fossils are relatively abundant in the Wahweap Formation, and suggest the presence of crocodylomorphs, as well as ornithischian and theropod dinosaurs. Evidence of invertebrate activity in this formation ranged from fossilized insect burrows in petrified logs to fossils of mollusks, large crabs, and a wide diversity of gastropods and ostracods.
Lythronax