Linhenykus monodactylus has been identified as the first dinosaur with just one finger. 

The new dinosaur belongs to the Alvarezsauroidea, a branch of the carnivorous dinosaur group Theropoda. Theropods gave rise to modern birds and include such famous dinosaurs as Tyrannosaurus Rex and Velociraptor.

This specimen is the only known dinosaur with one finger, and highlights the wide variety of evolutionary modifications of the hand that existed in different theropods.  


Artist's impression of Linhenykus monodactylus, © Julius T. Csotonyi

Most theropod dinosaurs have three fingers on each hand, but in most alvarezsauroids other than Linhenykus the two outer fingers are reduced to tiny, apparently useless structures. The presence of only one finger in Linhenykus, which is hypothesized to be a relatively primitive alvarezsauroid, shows that these vestigial fingers were not present in all members of the group.

The reasons for the loss of the two outer fingers in Linhenykus are unclear, and their disappearance may simply reflect the fact that they were no longer being actively maintained by natural selection