Thanatosaurus (Greek thneskos = death, sauros = lizard, "death lizard") was a relative of Nanotyrannus and T. rex that lived in North America of 66-65 million years ago. It was adapted to be the perfect killing machine combining the strength and size of tyrannosaurs with the stealth and agility of a Utahraptor.
Thanatosaurus was about 2.5 meters high and built like a juvenile T. rex, but much smaller, more agile, covered in feathers, two foot long three fingered arms, a longer snout, bigger skull and sharper, constantly replaced teeth that curve backwards and contain deadly poisons taken from local herbs, which kill over a period of three agonizing days. They have garnered a reputation as the smartest dinosaur, possibly rivalling Stenonychosaurus/Troodon in brainpower. Thanatosaurus is also believed to have been the deadliest dinosaur and might have been able to take on a Tyrannosaurus rex and win, which is a subject of intense debate among dinophiles. Though it wasn't very large, a Thanatosaurus, or worse, a pack of Thanatosaurus, would have been a sight that struck fear in every living denizen of the Cretaceous.