Tyrannosauroidea - Distribution

Distribution

The tyrannosauroids lived on the supercontinent Laurasia, which split from Gondwana in the Middle Jurassic, as well as on the northern continents, which separated from Laurasia later in the Mesozoic era. The earliest recognized tyrannosauroids lived in the Late Jurassic, including Guanlong from northwestern China, Stokesosaurus from the western United States and Aviatyrannis from Portugal. Some fossils currently referred to Stokesosaurus may instead belong to Aviatyrannis, given the great similarities in the dinosaur faunas of Portugal and North America during this time. If Iliosuchus from the Middle Jurassic of England is in fact a tyrannosauroid, it would be the earliest known genus and might suggest that the superfamily originated in Europe.

Early Cretaceous tyrannosauroids are also found on all three northern continents. Eotyrannus from England and Dilong from northeastern China are the only two named genera of this age, while Early Cretaceous tyrannosauroid premaxillary teeth are known from the Cedar Mountain Formation in Utah and the Tetori Group of Japan.

By the middle of the Cretaceous, tyrannosauroid fossils are no longer found in Europe, suggesting a localized extinction on that continent. Tyrannosauroid teeth and possible body fossils are known from the North American Dakota Formation, as well as formations in Kazakhstan, Tajikstan and Uzbekistan, from the middle of the Cretaceous. The first unquestionable remains of tyrannosaurids occur in the Campanian stage of the Late Cretaceous in North America and Asia. Two subfamilies are recognized. The albertosaurines are only known from North America, while the tyrannosaurines are found on both continents. Tyrannosaurid fossils have been found in Alaska, which may have served as a land bridge allowing dispersal between the two continents. Non-tyrannosaurid tyrannosauroids like Alectrosaurus and possibly Bagaraatan were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America. Eastern North America was divided by the Western Interior Seaway in the middle of the Cretaceous and isolated from the western portion of the continent. The absence of tyrannosaurids from the eastern part of the continent suggests that the family evolved after the appearance of the seaway, allowing basal tyrannosauroids like Dryptosaurus and Appalachiosaurus to survive in the east as a relict population until the end of the Cretaceous.

Basal tyrannosauroids may have also been present in what is now southeastern Australia during the Aptian of the Early Cretaceous. NMV P186069, a partial pubis (a hip bone) with a distinctive tyrannosauroid-like form, was discovered in Dinosaur Cove in Victoria, indicating that tyrannosauroids were not limited to the northern continents as previously thought.

An as yet undescribed and unnamed tyrannosauroid from the Zuni Basin of New Mexico has been found.