Researchers are suggesting that some dinosaurs likely survived the mysterious mass extinction of the Earth's prehistoric giant lizards because they had shrunk. Theropods, the dinosaur lineage that experts believe was the precursor to modern birds, were likely the only dinosaurs to shrink over time, according to a recent study.

The study, published in the journal Science, details how the fossil record boasts evidence of shrinking theropods over the course of 50 million years. Meanwhile, no other dinosaur linage showed the same consistency.

"Birds evolved through a unique phase of sustained miniaturization in dinosaurs," lead author Michael Lee, from the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum, said in a recent statement.

"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," he added. "Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins."

It has long been suspected that theropods like the infamous velociraptor were the ancestors of today's modern birds. Much about their sleek bipedal structure is similar to what we see today, especially among the predators of the sky.

Until very recently, theropods were also the only dinosaur lineage to boast evidence of feathers, even if these feathers were initially used for purposes other than flight.

According to the study, analysis of updated fossil records showed that theropods shrank at a rate (seen in at least 12 stages over 50 million years) that would lead directly to the size of known early birds and eventually to even today's modern versions.

"No other dinosaur group underwent such an extended period of shrinkage," Lee told Live Science, adding that ultimately "birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less-evolvable relatives could not."

The study was published in Science for August 1.