Washington - Scientists have mapped how a group of fearsome, massive dinosaurs evolved and shrank to become the first birds.

The surprisingly steady shrinking and elegant evolution of the dinosaurs over 50 million years is described in the journal Science.

Scientists focused on a family of two-legged, meat-eating dinosaurs called theropods. That suborder of dinos survives to this day as birds, however unrecognisable and improbable it sounds.

Theropods have been considered the ancestors of birds for a couple decades. But the new work gives the best picture of how they were transformed over time into the earliest versions of birds. (PTI)