A new dinosaur fossil from China has thrown paleontologists for a loop. The strange dinosaur has bony wing-like features that are wildly different from those of its close flying relatives and instead look more like those of a flying squirrel or a bat.
Many dinosaur fossils with bird-like designs have been found in China -- but this unusual specimen, described in the journal Nature, showcases a radically different (and defunct) prototype in the development of dinosaur and bird flight.
"Things have just gone from the strange to the bizarre," Kevin Padian of UC Berkeley, who was not involved in the work, wrote in a commentary on the study.
The odd fossil has been named Yi qi, meaning "strange wing" -- an apt description, given its unique features.
Yi qi appears to be a theropod, a category of dinosaurs that includes Tyrannosaurus rex, velociraptor and the ancestors of modern birds. And like many of the flying theropods that would give rise to modern birds, it's a bantamweight -- its skull is roughly four centimeters (or about 1.57 inches) long.
But Yi qi comes from a family known as Scansoriopterygidae, whose mere three known members have some very unusual features for theropods. Their third fingers are longer than their second fingers, for one thing. But Yi qi has an additional odd feature: a really long bone that juts out from the wrist at a sharp angle, far out of line with the actual finger bones.
"Documentation of the unique forelimbs of Yi greatly increases the morphological disparity known to exist among dinosaurs, and highlights the extraordinary breadth and richness of the evolutionary experimentation that took place close to the origin of birds," the authors wrote.
The bone looks like it could anchor some kind of wing -- and that idea is backed up by the remains of membranous tissue that was found between the strange jutting bone and the actual fingers. Yi qi's features don't look much like other flying theropods' more birdlike design; instead, they match the sort of features that might be found in the wings of pterosaurs, reptiles that evolved to fly independently of dinosaurs, or perhaps in the wings of bats or the skin flaps of gliders such as flying squirrels.
"Analogous features are unknown in any dinosaur but occur in various flying and gliding tetrapods," the authors wrote, "suggesting the intriguing possibility that Yi had membranous aerodynamic surfaces totally different from the archetypal feathered wings of birds and their closest relatives."
The scientists aren't sure whether Yi qi was a flier or a glider. But Padian argued that the dinosaur's wrist, hand and other skeletal elements appeared to be too short for powered flight.
"At present we can shelve the possibility that this dinosaur flapped," Padian said.
Padian also pointed out that even though the animal seemed to have structures that would have anchored a wing, its body didn't seem properly geared for flight. For example, according to the reconstruction, its body weight sat so far back that the animal would theoretically sag during flight and stall.
"We are left in a quandary: an animal with a strange structure that looks as if it could have been used in flight, borne by an animal that otherwise shows no such tendencies," Padian said. "And so far, there is no other plausible explanation for the function of this structure."
For now, that mystery will remain, as the specimen wasn't preserved below the ribcage.
The find, Padian added, "opens two cans of worms: about interpreting unique structures in fossils and about what it means to fly."