In 1874 Richard Owen named a new species of Pterodactylus, ‘P.’ sagittirostris, based on parts of the lower jaws of a single individual. The pterosaur was found in the Lower Cretaceous Upper Turnbridge Wells Sand Formation of southern England. In 1901, Harry Seeley transferred the species to the genus Ornithocheirus, which was used as something of a wastebasket taxon for any fragmentary pterosaur remains from Lower Cretaceous rocks in the United Kingdom. He noted that ‘O.’ sagittirostris and several other species assigned to Ornithocheirus were quite similar to each other, and gave them the informal designation “group 2.” In 1914 Reginald Hooley named the genus Lonchodectes, and included several of the “group 2” species in that genus, including ‘O.’ sagittirostris. In 2017, Stanislas Rigal, David Martill, and Steven Sweetman thought that it was distinct from Lonchodectes, and named a new genus to house ‘L.’ sagittirostris, Serradraco. The genus name translates to “saw dragon,” a reference to the distinctive saw-blade-like appearance of the teeth and jaws. The species name, sagittirostris, translates to “arrow snout.”
Despite its decades-long and confusing naming history, Serradraco is based on a single, partial lower jaw from a single individual. The middle portions of both jaws are known, with the right jaw fragment being about 12 cm (5 inches) long, and the left jaw fragment being about 7 cm (3 inches) long. The fragments show a uniform depth of about 2 cm (less than 1 inch), and are very narrow when seen from above, only about 1 cm (less than 1/2 inch) wide. There is a shallow groove on the external surface of both left and right jaws about 5 mm (less than 1/4 inch) below its upper surface.
The right jaw fragment has six tooth positions preserved with only two broken tooth fragments, and the left has five tooth positions preserved with four complete teeth. The teeth are slightly curved cones about 8-10 mm (less than 1/2 inch) long, and are inclined forward at about 20 degrees. At the base of each tooth, there is a bony collar or pedestal rising about 2-3 mm above the upper margin of the lower jaw. The upper margin of each collar or pedestal is perpendicular to each tooth, and are therefore angled at about 20 degrees.
In a 2013 review of the dozens of species once assigned to Ornithocheirus, Taissa Rodrigues and Alexander Kellner considered the distinctive bony collars on the base of the teeth of ‘L.’ sagittirostris to have been a result of damage when the specimen was originally cleaned by scientists, and therefore considered the species to be undiagnostic. However Rigal, Martill, and Sweetman disagreed after reexamination of the specimen, and considered the inclined collars real features. They noted that the inclined teeth and bony collars of Serradraco were unique among pterosaurs.
Cone-shaped teeth with raised bony collars or pedestals are found in lonchodectids, a mysterious and poorly-known lineage of Cretaceous pterosaurs with long and very narrow jaws. Without more complete remains, the broader relationships of lonchodectids have been difficult to figure out; although a recent analysis by Nick Longrich, David Martill, and Brian Andres found lonchodectids to be closely related to boreopterids within a larger lineage known as the ornithocheiroids. Most ornithocheiroids were marine fishers, although some were terrestrial carnivores.
When Serradraco lived about 135 million years ago, the area that would become southern England was a broad plain crossed by large braided rivers, an ideal hunting or fishing ground for Serradraco and other lonchodectids.