Dinosaurs may have evolved into smaller shapes over the course of 50 million years, allowing the animals to develop into birds, based on a new study.

Theropod dinosaurs were mostly carnivores, unable to fly. This new study examined the family trees of various types of dinosaurs, in an effort to determine any patterns in the evolution of the animals. More than 1,500 anatomical traits were examined in order to determine the lineage of species. Advanced mathematical modeling was employed to study how body sizes changed over time and across species. Researchers discovered that Theropods were the only variety of the animals that continually evolved into smaller forms.

"These bird ancestors also evolved new adaptations, such as feathers, wishbones and wings, four times faster than other dinosaurs," Darren Naish, Vertebrate Paleontologist at the University of Southampton, said.

Birds are most closely related to small varieties of dinosaurs, including the Microraptor, a tiny dinosaur with the ability to glide and climb trees. These creatures thrived roughly 120 million years ago. Evolution of Theropods into smaller species with additional bird-like characteristics, took place over at least 12 separate branches of the animals.

Several characteristics associated with small animals would have been enhanced by the evolution toward tinier species. These would include smaller snouts, larger eyes and brains, along with the retention of juvenile physical characteristics. A lighter body mass would have also contributed to aerial abilities of the animals, according to researchers.

"Being smaller and lighter in the land of giants, with rapidly evolving anatomical adaptations, provided these bird ancestors with new ecological opportunities, such as the ability to climb trees, glide and fly. Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins," Michael Lee of the University of Adelaide said.

When the Earth was struck by an asteroid 65 million years ago, the impact wiped out vast swaths of forest, and set forest fires ablaze worldwide, leading to dramatic cooling of the Earth. Sea levels fell, wiping out many species of marine life, creating a scarcity of food that worked its way up the food chain. Primitive birds, able to gain access to higher ground, may have survived where their larger cousins died out.

Michael Lee produced a video showing how Theropod dinosaurs evolved into smaller forms over time, developing into the world's first true birds.

Study of theropod dinosaurs, and how continually smaller bodies could have led to the rise of modern avian species was profiled in the journal Science.