In 2010 paleontologists Lü Junchang and Fucha Xiaohui named Archaeoistiodactylus linglongtaensis, a new monofenestratan pterosaur. It was found at the Linglongta locality in the Middle to Upper Jurassic Tiaojishan Formation in Liaoning, northeastern China. The genus name means “ancient Istiodactylus,” referencing Lü and Fucha’s initial idea that it was the earliest istiodactylid. The species name honors the Linlongta locality.
Archaeoistiodactylus is known from a single incomplete associated skeleton. The rear part of the skull, most of the mandible, and some limb bones. The skull is represented by the area around the jaw joint, and the tooth-bearing maxilla. Although the skull is incompletely preserved, the nasoantorbital fenestra was apparently quite large. There is at least one tooth preserved in the maxilla, and it’s recurved, relatively short, and stout. The teeth in the lower jaws were widely spaced with circular roots. Unusually, there appears to be a midline tooth at the tip of the lower jaw, a unique feature among pterosaurs.
The postcranial skeleton is partially articulated, but heavily damaged, and was only preliminarily described by Lü and Fucha. Unlike istiodactylids and other short-tailed pterosaurs, the bones of the metacarpus were still fairly short. Archaeoistiodactylus was a small pterosaur, with a wingspan of about 75 cm (2.5 feet), about the same size as a magpie.
When they first named Archaeoistiodactylus, Lü and Fucha linked it to the istiodactylids because of the large nasoantorbital fenestra and similarly shaped maxillary teeth. In 2011, David Martill and Steve Etches thought that this was in error, and the specimen was probably a poorly preserved Darwinopterus. In a 2014 review of the Tiaojishan fauna, Corwin Sullivan and colleagues also doubted the istiodactylid affinities of Archaeoistiodactylus. They too thought that it was similar to Darwinopterus and other wukongopterids because of the combination of a large nasoantorbital fenestra and a short metacarpus. They did point out that the midline tooth in the lower jaw set Archaeoistiodactylus apart from other pterosaurs. Wukongopterids were transitional between the early long-tailed forms and short-tailed pterodactyloids that first emerged at the end of the Jurassic and came to dominate the Cretaceous skies.
Like other wukongopterids, Archaeoistiodactylus probably ate insects, other invertebrates, and small vertebrates. It lived in a well-watered temperate to subtropical forest 160-165 million years ago.