T. rex Ancestor Shared the Lizard King's Smarts, But Not Its Size

An artist's reconstruction of Timurlengia eutoica. (Credit: Todd Marshall) For a few million years at the end of the Cretaceous period, before dinosaurs went extinct, Tyrannosaurus rex dominated the landscape. The fearsome predator with an oversized head and tiny forearms has become synonymous with the word dinosaur, thanks in no small part to movies such as Jurassic Park. But how T. rex came to rule the roost has remained a bit of a mystery. The earliest tyrannosauroids were about as tall as a human, which is a far cry from the widely recognized 13-foot-tall, 40-foot-long killers that dominate museum entrances today. Now, combing through fossils unearthed in Uzbekistan, paleontologists have discovered a horse-sized cousin to the T. rex that fills a 20-million-year hole in its ancestry.