In 2004 Michael Maisch and colleagues described a new genus and species of dsungaripterid pterosaur, Lonchognathosaurus acutirostris, from the southern Junggar Basin in Xinjiang, northwestern China. The species is so far only known only from a partial skull found in the Lower Cretaceous Lianmuxin Formation, home to at least two other species of dsungaripterids. The genus name translates to “lance jaw lizard” in Greek, and the species name translates to “sharp beak” in Latin.
The fragmentary skull preserves the front half of the upper jaws. It is in two pieces: a very long and tapering portion representing the very tip of the upper jaw, and a second portion from immediately behind the first. In profile, the upper jaws are extremely long and narrow, with more or less straight upper and lower margins. The front of the nasoantorbital fenestra can be seen at the very back of the skull fragment.
On the upper surface of the skull is a narrow sagittal crest which rises abruptly from the rostrum. It has a concave front edge and resembles a cresting wave. The crest has numerous grooves and ridges that run parallel the concave front margin, but become more vertically oriented further back. In life, this crest probably ran back and beyond the rear of the skull and was likely expanded vertically by soft tissues making it broadly fan-shaped.
The tips of the jaws are completely toothless, and there are eight tooth positions present farther back. The eighth tooth socket emerges just in front of the nasoantorbital fenestra and appears to be the last tooth position in the upper jaws. Each tooth socket is ringed by a low bony collar similar to what’s seen in other dsungaripterids, but much less extreme than the condition in Dsungaripterus itself.
Nothing else is known of the skull or skeleton. Maisch and colleagues estimated that the complete skull would be about 40 cm (16 inches) long. Comparison to other dsungaripterids suggests a wingspan of roughly 3 meters (10 feet).
When Maisch and colleagues initially described Lonchognathosaurus in 2004, they compared it to other dsungaripterids as well as germanodactylids which have similar dentition. They noted several differences between Lonchognathosaurus and its contemporaries Dsungaripterus and Noripterus. Dsungaripterus is overall more robust, has twelve pairs of teeth in the upper jaws with each tooth is almost completely surrounded by bone, and the toothless jaw tips curve upward. Noripterus has straight jaw tips and less developed bony collars like Lonchognathosaurus, but that genus has at least fifteen pairs of teeth in the upper jaws, and a crest with a convex rather than concave front edge.
Despite these difference, Brian Andres and colleagues considered Lonchognathosaurus to be a specimen of Dsungaripterus in 2010, and Hone and colleagues considered it to be a specimen of Noripterus in 2017. Conversely, when describing new cranial material of Noripterus in 2009, Lü and colleagues considered Lonchognathosaurus to be a distinct and valid taxon.
When Lonchognathosaurus lived, about 120 million years ago, the Junggar basin was bound by hills and mountains and home to a large lake. Dsungaripterids were quite common in inland basins at the time, sometimes being the only pterosaurs known. They likely used their long toothless jaw tips to probe for mollusks and crustaceans, crushing them with their reinforced jaws and teeth.