杏吧原创

A two-fingered dinosaur may help researchers better understand how animals lose fingers and toes through evolution.

Oviraptorids, a group of bird-like dinosaurs that lived in what is now China and Mongolia 100 million years ago, usually had three fingers on each hand. But a set of juvenile skeletons confiscated from fossil poachers at the Mongolia-China border in 2006 have revealed two-fingered hands, suggesting an adaptation.

Gregory Funston at the University of Edinburgh in the UK and his colleagues have named the dinosaurs Oksoko avarsan, after a three-headed eagle in Mongolian mythology and the Mongolian word for 鈥渞escued鈥�. The dinosaurs had a toothless beak and were probably covered in feathers like other oviraptorids, which share a common ancestor with birds, says Funston, making them resemble a small ostrich.

Unlike its three-fingered relatives, the new species had shorter forearms and only two functional, stout fingers with a limited range of motion 鈥� a remnant stub of a third finger bone doesn鈥檛 emerge from the hand. That means it may have used its hands for nest-building instead of grabbing prey, says Funston. 鈥淭hey might have been moving towards becoming herbivores.鈥�

Over millions of generations, animals evolve away body parts that become less useful 鈥� including unneeded fingers and toes, says Funston. It is akin to the loss of the tail in humans after they evolved to walk upright. 鈥淚t requires energy to grow and maintain each structure, so if it鈥檚 not needed, the energy is better spent elsewhere,鈥� he says.

Funston and his fellow researchers acquired the skeletons after Mongolian customs officials confiscated them from black market fossil traders, he says. While this was enough to confirm the discovery of a new species, the illegal nature of the excavation prevented a full investigation. In particular, the scientists don鈥檛 know where the fossil was found, so they can鈥檛 study the animals鈥� environment. 鈥淚t鈥檚 kind of bittersweet,鈥� says Funston.