Bizarre dinosaur only had one finger on each arm

A newly-discovered, one-fingered dinosaur is the strangest proof yet that if you don't use it, you lose it.

Linhenykus monodactylus lived from about 84 to 75 million years ago in the late Cretaceous. It was a tiny creature that weighed less than half a kilogram, although it was a relative of much larger beasts like the T. rex. The newly discovered dinosaur is the most extreme example yet of an evolutionary trend among carnivorous dinosaurs, in which their fingers withered away to weak stumps. In the artist's conception above, you can see just how odd these lone fingers looked on the dinosaur.

Linhenykus is an alvarezsaur, a type of dinosaur known for finger reduction. Lots of other species have been found that only have a single strong finger that was probably used for digging - Linhenykus's fingers resemble similar structures found on modern diggers like armadillos - while the other digits are practically useless. The researchers can actually put a lot of these dinosaurs in a rough evolutionary sequence, tracing the gradual wearing away of fingers until Linhenykus (and any other dinosaur species like it) emerged as the uni-clawed end of this particular evolutionary sequence.

But the story isn't quite so simple. The researchers point out that Linhenykus slots in between other species with withered fingers, suggesting species first lost their fingers through evolutionary processes and then got them back again. It's certainly not unheard of, but this is one of the best examples of how evolution really can oscillate back and forth, and a good reminder that evolution doesn't have endpoints...even when those endpoints are weird, lonely fingers.

[Proceedings of the National Academy of Sciences]