In the 1970s, paleontologists discovered several finely preserved skeletons of pterosaurs in the Upper Triassic Zorzino Limestone near the town of Cene, Lombardy in northern Italy. First discovered was Eudimorphodon ranzii in 1973, then the tiny Peteinosaurus zambellii in 1978. Peteinosaurus is based on two partial specimens. The first of these specimens is incomplete, represented by portions of the lower jaw, and scattered parts of both wings and legs. The second example is a very well preserved specimen in articulation, but missing the head and neck.
The lower jaw of Peteinosaurus is very long and thin with parallel upper and lower borders. The bone is lined with many small teeth. The teeth are shaped like curved blades, closely packed, and except for the first two teeth, are uniformly small. The wings are robust, relatively short — at only twice the length of the legs — with a wingspan of only 60 cm (24 inches), about the same size as a magpie.
The claws on the hands and feet were large and curved. Peteinosaurus also had a very long, bony tail which, at over 15 cm (6 inches) made up at least half of its total length. The tail vertebrae bore long extensions overlapping several vertebrae back. This made the tail fairly stiff, but also flexible, similar to a fishing rod. Peteinosaurus may have had a vertical fin on the end of its tail, like what is seen in many other long-tailed pterosaurs.
When first described, Peteinosaurus was regarded as a close relative of the puffin-faced Dimorphodon macronyx, from the Early Jurassic of the UK. Subsequent researchers initially supported this view, but most recent research suggests that Peteinosaurus is more closely related to Eudimorphodon. Multiple researchers have found it to be part of a lineage of small, exclusively Triassic, and mostly European pterosaurs. This group, called Eopterosauria, is the first major radiation of pterosaurs and includes the eudimorphodontids, preondactylians, and Peteinosaurus.
Eopterosaurs, including Peteinosaurus, were uniformly small and probably had a varied diet of fish and small terrestrial vertebrates and invertebrates. The robust limbs and large claws suggest that Peteinosaurus may have spent a lot of time clamoring about in trees in search of food.