In 1998, paleontologists Ji Shu’an and Ji Qiang named a newly discovered pterosaur species Dendrorhynchus curvidentatus from the Middle Jurassic Tiaojishan Formation of northeastern China. The following year, the genus name was modified to Dendrorhynchoides, as “Dendrorhynchus” was already used as the generic name of a protozoan that parasitizes the guts of certain fly species. The name Dendrorhynchus is derived from the Ancient Greek words “dendro” meaning tree and “rhynchus” meaning beak, and was meant to be a an allusion to Rhamphorhynchus, then thought to be a close relative. Dendrorhynchoides adds the Ancient Greek suffix “-oides” meaning looks-like. The species name curvidentatus is derived from Latin, and means curved teeth. In 2012, Lü Junchang and David Hone named a second species of Dendrorhynchoides, D. mutoudengensis based on a second specimen found near the town of Mutoudeng, Hebei Province.
Both specimens are very small, with the specimen of D. curvidentatus being more complete than that of D. mutoudengensis. Nevertheless, both provide important information about the anatomy. The skulls of both specimens are crushed and difficult to interpret, but it is clear that they have remarkably short and broad snouts, with skull length slightly less than skull width. The teeth of the two specimens are different however, with D. curvidentatus having short, curved teeth, and D. mutoudengensis having two types of teeth: shorter cone-like teeth, and longer curved teeth.
The vertebrae of the neck and torso are largely complete in the D. curvidentatus specimen, and show that it had a short neck, and relatively compact body. This specimen had been modified by private fossil dealers prior to description by scientists. The dealers had added the tail of what appears to be a small dromaeosaur to make it appear more complete and probably fetch a higher price. The real tail of D. curvidentatus is incomplete, but the second species does have the entire tail present, and it is remarkably short, only about 85% the length of the femur.
Both specimens are preserved on their backs or bellies, with the wings and legs splayed to the side. They have very short hands, similar to early pterosaurs and unlike other short-tailed pterosaurs. The wing membrane stretched from the tip of the wing-finger to the ankles, and another wing membrane stretched from the long fifth toe to the tail, making the tail essentially invisible. The wingspan of both specimens is about 40cm (16 inches), roughly the same as most living swallows.
When originally, described, Ji and Ji considered Dendrorhynchoides to be a close relative – and possibly the same genus as – Rhamphorhynchus from the Upper Jurassic Germany (hence the name). This was largely due to the short hands, and added dromaeosaur tail; dromaeosaurs have long and overlapping extensions of the tail vertebrae, looking remarkably similar to the tails of rhamphorhynchids. Not long after its initial description, the discovery of the forgery and the short, wide skull led researchers to realize that Dendrorhynchoides is actually an anurognathid. Anurognathids are all small, short-snouted pterosaurs known from Middle Jurassic to Lower Cretaceous rocks.
Anurognathids are difficult to place on the family tree of pterosaurs due to their small size, delicate and often crushed skull bones, and strange mix of skeletal characteristics. Many researchers have found anurognathids to be among the most primitive pterosaurs due to their short necks and hands, having convergently lost their tails. Alternatively, some researchers have found the anurognathids to be the closest relatives of the short-tailed pterodactyloids which were to dominate the skies in the Cretaceous. Pterodactyloids all had long skulls and necks, and greatly lengthened hands, unlike what is seen in anurognathids. This would-be transitional position is complicated by the wukongopterids, a small family of pterosaurs known from Middle Jurassic rocks that have lengthened skulls, necks, and hands, but retained fairly long tails, and appear to be more straightforward transitional forms.
Regardless of their phylogenetic position, anurognathids like Dendrorhynchoides have been regarded as insect-eaters because of their wide mouths and small sharp teeth. Dendrorhynchoides and the other anurognathids also show other features pointing to hunting insects while flying including large eyes, and narrow wings. They were likely acrobatic fliers, filling a similar ecological role as modern swifts, swallows, nightjars, and bats. The two Dendrorhynhoides species lived in a temperate forest, alongside fellow anurognathid Jeholopterus. These three species all hunted flying insects, but may have preyed upon different species or hunted in different ways to avoid direct competition.