The fossil of a newly discovered species of scansoriopterygid dinosaur with bat-like wings, found in Liaoning Province, China, is described in a paper published this week in Nature. This specimen, dated to around 163 million years ago, provides further evidence that suggests that dinosaurs closely related to birds experimented with different wing structures near the origins of flight.
The scansoriopterygids form a group of tiny dinosaurs (around 200 grams) that are generally reconstructed as feathered tree climbers, with very long hands and fingers. However, the recently discovered scansoriopterygid dinosaur Yi qi was different. In addition to feathers, Y. qi had what appeared to be bat-like, membrane wings supported by a styliform - a long, pointed wrist bone. This type of membranous wing has been used by lineages of non-dinosaur flying vertebrates such as bats and pterosaurs, but was previously unknown among the theropod dinosaurs.
Min Wang and colleagues describe a scansoriopterygid named Ambopteryx longibrachium, which has membranous wings and a styliform, similar to Y. qi. However, several features distinguish Ambopteryx from its cousin, including a wider forelimb bone, a short tail ending in fused vertebrae and an elongated forelimb that is longer than the hindlimb.
The authors show that marked changes in wing structure evolved near the split between scansoriopterygids and the bird lineages, as the two underwent different paths to becoming airborne. They suggest that the membranous wings and elongated forelimbs present in scansoriopterygids probably represent a short-lived experimentation with flight, which occurred before the later predominance of feathered wings.