Lythronax

About Lythronax

Characteristics: The Completed "Qualities of a King"

Lythronax was a carnivorous dinosaur of the Tyrannosauridae family that lived in North America during the Late Cretaceous period (about 81.9 to 81.5 million years ago). It reached a total length of about 5 to 8 meters and a weight of about 500 kilograms to 2.5 tons, possessing a heavily built body.

Its most prominent feature is the shape of its skull. Even though Lythronax is one of the oldest known members of the tyrannosaurid family, it had a short, broad face very similar to that of Tyrannosaurus rex. Furthermore, because the back of its skull was wide, its eyes faced forward, allowing for a wide field of "binocular vision (stereoscopic vision)."

This discovery showed that the "advanced hunting abilities" seen in tyrannosaurs were perfected more than 10 million years earlier than previously thought, contributing significantly to the study of tyrannosaurs.

Lythronax also had extremely powerful jaw strength and thick, robust "banana-shaped" teeth. It is believed that they could not only strip meat from their prey but also perform forceful hunting by crushing bones.

Lythronax's Athletic Ability and the Secret of Its Growth

Despite its massive body, Lythronax possessed high athletic ability. The secret lies in the bone structure of its hind limbs. The bones in its instep were wedge-shaped, with the middle bone firmly squeezed between the bones on either side.

Furthermore, tyrannosaurid dinosaurs significantly changed their appearance and roles depending on their growth stage. In their youth, they were light and agile small predators, but as they entered their growth period, their weight increased rapidly, transforming them into apex predators with massive jaws. It is thought that by changing their prey according to their age group, they avoided competing for food with each other.

In terms of appearance, it is known that tyrannosaur ancestors had feathers, but if a large dinosaur reaching several tons like Lythronax were covered in feathers, there would be a risk of its body temperature rising too high. Therefore, it is highly likely that adults were covered in crocodile-like scales to easily release body heat.

Evolution on the Lost Continent of Laramidia

During the Late Cretaceous period when Lythronax lived, the Earth was very warm and sea levels were high, creating a shallow sea across the center of the North American continent. This divided the continent into east and west, with the western side becoming a long, narrow island continent called "Laramidia." Lythronax was the apex predator that reigned over the southern part of this continent of Laramidia.

As sea levels rose further, the interior of the Laramidia continent was also separated by seas by region, and dinosaurs could no longer travel back and forth. Because of this "geographic isolation," the evolution of dinosaurs progressed to suit their unique environments.
As a result, tyrannosaurids with different characteristics prospered in the northern regions (such as present-day Canada) and the southern regions (such as present-day Utah). The short, robust skull of Lythronax is also believed to be the result of unique evolution in this isolated southern region.

Discovery and Description

In 2009, Lythronax fossils were discovered in the "Wahweap Formation" at the Grand Staircase-Escalante National Monument in southern Utah, USA. Parts of the right upper jaw, snout, top of the skull, lower jaw, and some leg bones were excavated together.
By measuring the volcanic ash in the stratum, it was identified as dating from about 81.9 million to 81.5 million years ago.

Then, in 2013, a research team led by Dr. Mark Loewen described it as a new genus and species, "Lythronax (Lythronax argestes)." The discovery of this large theropod, meaning "King of Gore," provides an important key to unraveling when, where, and how tyrannosaurid dinosaurs evolved into their terrifying form.