The findings are frequently driven by the discoveries of many fossils of smaller tyrannosaurs
"Early in their evolution, tyrannosaurs
hunted in the shadows of archaic lineages such as allosaurs that were already established at the top of the food chain."
It "captures tyrannosaurs
at a key point in their evolutionary transformation," notes Lawrence Witmer, who studies the soft tissues of dinosaur heads at Ohio University, Athens.
A fossil from a new species of dinosaur is helping to bridge a crucial 20-million-year gap in tyrannosaur
The long-nosed tyrannosaur
's bones were discovered by workmen on a construction site in China.
Until now, only two fossilised tyrannosaurs
with elongated heads had been found, both of which were juveniles.
Edinburgh's Dr Steve Brusatte said: "This is a different breed of tyrannosaur
. It has the familiar toothy grin of T- rex, but its snout was much longer and it had a row of horns on its nose.
Spinosaur teeth are smooth and shaped liked cones--more like those of modern crocodiles than of tyrannosaurs
. An analysis of the chemical makeup of the teeth turned up even more evidence.
A team led by Dr Paul Serano examined the fossils and their importance was revealed when it became clear this was an adult dinosaur bearing all the hallmarks of later giant tyrannosaurs
but at a fraction of the size.
The new evidence suggested that for most of their time on Earth, tyrannosaurs
may have been living in the shadow of larger dinosaurs.
However, it also held surprises: A lot of dinosaurs would have looked really strange because they were completely feathered--like the recently discovered tyrannosaur
, which we named Dilong paradoxus, meaning "surprising emperor dragon." It wasn't the first feathered dinosaur discovered, but it was the first tyrannosaur
ever found with primitive feathers.