Beipiaopterus

In 2003 Junchang Lü named Beipiaopterus chenianus, a newly discovered ctenochasmatid pterosaur from the Lower Cretaceous Yixian Formation, near Beipiao City, Liaoning, China. So far, Beipiaopterus is known from a single incomplete specimen preserving numerous patches of skin. The genus is named for Beipiao City, and the species name honors paleontologist Peiji Chen. 

The single specimen is mostly articulated but incomplete, missing the skull and adjacent part of the neck, as well as the right wing. The four last neck vertebrae are present, and elongate. The left wing and shoulder moved away from the torso before burial, but remained in articulation with the body. Beipiaopterus is unique among ctenochasmatids, as the wing finger appears to be made up of just three phalanges. All other pterosaurs except some nyctosaurids have four wing finger phalanges. Beipiaopterus was a small pterosaur, with a wingspan just over one meter (39 inches), about the same size as a mallard duck. 

The specimen preserves portions of the left wing membrane near its end, and the right wing membrane close to the knee, as well as hair tufts on its neck, and webbed toes on its left foot. The wing membrane preserved near the end of the wing has many stiffening fibers, known as actinofibrils, that are nearly parallel to the wing finger and helped the distal wing keep a fairly rigid shape. The membrane preserved close to the knee shows that the epidermis was very thin and highly vascularized, possibly helping Beipiaopterus regulate its body heat like living bats. 

Lü considered Beipiaopterus to be a ctenochasmatid when first described, citing proportional similarities to the family of suspension-feeding pterosaurs commonly found in Upper Jurassic and Lower Cretaceous rocks around the world. Lü considered it to be particularly close to Eosipterus, also known from the Yixian Formation, and differentiated the two based on proportions of limb elements and the presence of the fourth wing finger phalanx in Eosipterus. Subsequent phylogenetic analyses performed by Brian Andres have confirmed that Beipiaopterus as a ctenochasmatid most closely related to Eosipterus and Gegepterus, also from the Yixian Formation. These three are ctenochasmatine ctenochasmatids, closest to Pterodaustro and Ctenochasma. 

All ctenochasmatids have long narrow snouts lined with dozens to hundreds of laterally projecting needle-shaped teeth. Beipiaopterus was probably most similar to other ctenochasmatines like Ctenochasma and Gegepterus which have gently curving jaws and long teeth in the upper and lower jaws. 

Ctenochasmatids were suspension feeders, using their teeth to filter small prey items from the water, mud, and weeds. Beipiaopterus lived 125 million years ago in a temperate forest with numerous rivers and lakes. Several other ctenochasmatids and other pterosaurs have been discovered in rocks of the Yixian Formation in addition to hundreds of birds and other feathered dinosaurs.