Episode 52 is all about Lythronax, the earliest known tyrannosaurid from Laramidia.

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In this episode, we discuss:

• The dinosaur of the day: Lythronax
• Tyrannosaurid theropod that lived in what is now Utah
• Lived in late Cretaceous
• Species is L. argestes (known from an adult specimen consisting of a nearly complete skull, pubic bones, tibia, fibula, metatarsals)
• Name means Gore King
• The name uses King, like T-rex, because it’s so similar to T-rex.
• Argestes refers to the area in Utah where the fossils were found
• Bones discovered in 2009 in Utah (Grand Staircase)
• The Wahweap Formation where it was found is part of the Grand Staircase region (talked about on podcast), which had a wet, seasonal climate and lakes, floodplains, and rivers
• Grand Staircase-Escalante National Monument has been described as “the last great, largely unexplored dinosaur boneyard in the lower 48 states,” according to Scott Sampson
  Lived on Laramidia (a landmass separated from North America by a seaway)
• Earliest tyrannosaurid from Laramidia
• Oldest known tyrannosaurid (also most complete specimen from southern Laramidia)
• Laramidia was swampy, coastal, subtropical “island continent”
• Earlier tyrannosaurs were smaller (like Guanlong)
• Took a year to excavate Lythronax. Specimen now houses in the Natural History Museum of Utah in Salt Lake City
• Took 10 months to prepare Lythronax bones, done mostly by volunteers
• Officially named in November 2013
• Study was published in 2013
• Bipedal carnivore
• 26 ft (8 m) long and 5,500 pounds or 2.5 tons (based on close relatives)
• Lythronax had forward facing eyes, narrow snout, and wide back of the skull, which researchers thought didn’t appear until 70 million years ago (but Lythronax was 10 million years earlier than that)
• Skull is like a T-rex, with eyes facing front (had depth perception)
• Skull also similar to Tarbosaurus
• T-rex lived 10-12 million years later than Lythronax, which probably evolved in isolation on Laramidia
• Probably showed that different tyrannosaur species lived in north and south Laramidia at the same time
• Then the seaway grew smaller but climate variations and different food sources may explain why late Cretaceous dinosaurs in western North America were different from dinosaurs on other continents at the same time
• Because geologically Lythronax is the oldest known tyrannosaurid and is most closely related to T-rex and Tarbosaurus, the geologically youngest tyrannosaurids, the tyrannosaurid group probably diversified earlier than 80 million years ago, so there are probably a lot of other unknown tyrannosaurids to be discovered
• Some tyrannosaurids probably immigrated to Asia around the end of the Cretaceous (originated in northern Laramidia, western North America, with many species moving to souther Laramidia)
• The study analyzed 501 skeletal features and 54 species of carnivorous dinosaurs (and found Lythronax to be most closely related to T-rex and Tarbosaurus
• Had large teeth “banana-shaped meat cleavers” (though smaller than bananas) and serrated; probably used them to crush bone and slice flesh (could probably swallow meat whole)
• Teeth described as banana like because they are round and curved back
• Probably largest predator of its time and place
• Herbivores in the area included hadrosaurs, ankylosaurs, and ceratopsians
• Can see the skull at the Natural History Museum of Utah
• Tyrannosauridae (means “tyrant lizards”) are theropods
• Two subfamilies with up to 11 genera (number of genera is controversial, some think only 3)
• Lived late Cretaceous, Asia and North America
• Usually the largest predators
• Largest species was T-rex
• Not many complete specimens found for known tyrannosaurids
• But many genera have complete skulls
• Some tyrannosaurids had crests above eyes
• Small arms but long legs
• Juvenile tyrannosaurids had longer legs, more suited to running fast, but that changed as adults
• Scientists used to think tyrannosaurids moved between Asia and North America via the Bering Strait, but now they think all Asian tyrannosaurids were part of one evolutionary lineage
• Fun fact: Anthony Maltese on his blog described the process of putting together a Daspletosaurus bone that started in many pieces, which includes using glue, epoxy, and cement.