When you think of tyrannosaurs, the first thing that probably comes to mind is the terrifying, giant predator from the Jurassic Park movies – but even the biggest names have to start small. Palaeontologists have now filled in more of the creature's modest roots, in the form of a new species of tyrannosauroid that was probably smaller than you.

Dug up in the US state of Utah, the new species has been named Moros intrepidus. For now it's known from a few leg bones and some teeth, but the discoverers have worked out that the creature would have grown to just 1.2 m (3.9 ft) tall at the hip and weighed a petite 78 kg (172 lb). That makes it an absolute featherweight compared to its great-great grandkids like T-Rex, which routinely stood 3.6 m (12 ft) tall and topped out at 8 tons.

This tiny tyrannosaur also helps patch up some holes in the dinosaur family tree. It's currently thought that the biggest species of tyrannosaurs, like T-Rex or Albertosaurus, only really lived for the last 2 million years before the asteroid rebooted life on Earth 66 million years ago. Older fossils, particularly from Asia, show that about 100 million years prior to that, tyrannosaurs were much smaller.

But between those two extremes, there's a 70-million year gap in the North American fossil record. M. intrepidus helps plug it up, with its discoverers dating it to about 15 million years before the next earliest-known, North American tyrannosaur. According to the researchers, that means the creatures had their evolutionary growth spurt in 16 million years or less.

The discovery of M. intrepidus is just the latest in a long line of new details we've learned recently about everyone's favorite kind of dinosaur. In the last few years alone, scientists have reshaped our understanding of them by revealing they were even larger than you imagine, boasted one of the strongest bites of any land animal in history, had surprisingly sensitive snouts – and probably couldn't really run or roar.

The research was published in the journal Communications Biology.