Count evolution on the fingers

Scientists have long believed that birds inherited their three-fingered claws from dinosaurs.

The transition from five fingers to three took place while dinosaurs still roamed the Earth but a long-running controversy has centred on which two fingers were lost through natural selection.

The conventional wisdom has long been that the most advanced species of therapods, the dinosaurs who are the ancestors of today's birds, lost the last two fingers on their hands — or, to anthropomorphise, the “ring finger'' and the “little finger''.

A new dinosaur find in China suggests a different answer: The first and the fifth fingers were lost.

Scientists said that a dinosaur found in a 159-million-year-old deposit in a mine in northwestern China was a transitional beast between five-fingered and three-fingered creatures and that the fossil revealed an animal whose first finger had shrunk sharply and whose second finger had greatly increased in size.

Finger facts

James Clark, of the George Washington University, and his colleagues said each subsequent finger on the dinosaur took on the shape of the digit next to it, eliminating the last finger as well.

The recently discovered dinosaur has been dubbed Limusaurus inextricabilis.