A new study has revealed that dinosaurs' unique ability to shrink explains the evolutionary transformation that led them to their present form of birds. Throughout the evolution process, this ability helped the species adapt to new ecological niches.

The study was conducted by the Royal Ontario Museum and an international team led by scientists from Oxford University. After measuring the thickness of the leg bones from 426 species of dinosaurs, researchers were able to estimate the animals' body mass. They learned that dinosaurs showed signs of rapid body size evolution around 220 million years ago. However, the rate somehow slowed down within the 170 million years that followed. During this period, only the evolutionary line that led dinosaurs to become birds showed a change in size.

Analysts from the team said that the bird's small size could explain its evolutionary potential. This lower body size limit is broken by around 1 kilogram observed in other dinosaurs.

Ascertaining the weight of a dinosaur can be done by determining the thickness of its leg bones, such as the femur.

"This is quite reliable," said team member Dr. Nicolas Campione of Uppsala University in a press release.  

The Argentinosaurus was previously recorded as the biggest dinosaur, with a weight of 90 tons. This was 6 million times heavier than the smallest Mesozoic dinosaur, identified as Qiliania. The sparrow-sized bird weighed less than an ounce. These records show that the body plan of dinosaurs was truly versatile.

But some dinosaur groups failed to evolve, stuck in narrow ecological niches that ultimately led to their extinction. This led researchers to the conclusion that the capacity to evolve in different sizes was important to the dinosaurs' success factor.

Details of the research can be read on the May 6 issue of PLOS Biology.