Nanotyrannus lethaeus

Nanotyrannus is a medium-sized tyrannosauroid from the Late Cretaceous of North America. It was longer-legged and more gracile than Tyrannosaurus, and at 6-8 m (20-25 feet) long, much smaller in overall body size.

Nanotyrannus was initially based on a somewhat crushed skull and jaws, and the last two decades saw a prolonged debate over whether purported Nanotyrannus specimens were their own, smaller species or represented juvenile stages of Tyrannosaurus rex. This was settled decisively in 2025 when a study of the “Bloody Mary” specimen showed it was an adult of the type species, Nanotyrannus lancensis. The same paper also recognized the Jane specimen (BMRP 2002.4.1, figured here) as a near-adult morph of a second species of Nanotyrannus, N. lethaeus, although this may prove to be somewhat more controversial.