In February 2017, paleontologists Chang-Fu Zhou and colleagues described a new species of pterosaur, Liaodactylus primus, from the Tiaojishan Formation in Liaoning, China. The Tiaojishan was deposited 160 million years ago, during the early Late Jurassic. Liaodactylus is known from a well-preserved skull and mandible as well as two neck vertebrae.
The skull is very long and narrow, and about 13 cm (5 inches) long. The snout makes up more than half of the skull's length, bearing more than 150 teeth in total. All teeth are inclined outwards and curved slightly inward, forming an interlocking basket of teeth when the jaws are closed. The teeth are more tightly packed and longer near the tips of the jaws. Although only known from a skull and some neck vertebrae, comparison to similar pterosaurs suggest its wingspan was about 40 cm (16 inches).
Liaodactylus lived in a humid subtropical forested environment dotted by lakes and crossed by rivers. Liaodactylus used its numerous teeth to grasp or filter small animals out of the water, similar to living flamingos. Zhou and colleagues point out that Liaodactylus is the earliest known filter-feeding pterosaur, a mode of life present in some pterosaurs for the next 60 million years.
Liaodactylus was a ctenochasmatid, a large group of filter-feeding pterosaurs found in Upper Jurassic and Lower Cretaceous rocks in mostly northern continents. Liaodactylus is both the earliest ctenochasmatid, and one of the earliest pterodactyloids. Pterodactyloidea is the enormous lineage of short-tailed pterosaurs that dominated the Cretaceous skies. Zhou and colleagues compared Liaodactylus and the ctenochasmatids to their closest relatives. They found that the filter-feeding ctenochasmatids evolved from small fish-eating pterosaurs. Even within the ctenochasmatids, the teeth become more efficient filters in later species.