In 2011, paleontologists Shunxing Jiang and Xiaolin Wang described Pterofiltrus qiui, a small, new pterosaur from the Lower Cretaceous Yixian Formation of northeastern China. Pterofiltrus is only known from a single disarticulated skull and two damaged neck vertebrae. The name Pterofiltrus is derived from the Ancient Greek word “pteron” meaning wing and the Latin word “filtrus” meaning filter. The species name honors paleontologist Zhanxiang Qiu.
The skull itself is preserved in three segments, the snout, the braincase region, and the mandible. The snout segment is very long and tapered, with a large number of long thin teeth filling at least two-thirds of the upper jaw. The snout segment is lying on its left side, and the teeth appear to be vertically oriented, but the tooth sockets themselves seem to show the teeth near the tips of the jaw were angled more horizontally in life. The braincase region includes not just the braincase, but the bones housing the jaw muscles and the upper jaw joint. It had drifted away from the snout, and came to rest next to the snout teeth.
The mandible had also drifted away from its life position, and was found on the upper side of the snout segment, and largely disarticulated. It had numerous needle-like teeth and it appears to have been oriented almost horizontally in life, like that of the upper jaw. The mandible is unusual because its symphysis – the joint joining the right and left sides – is well over half the length of the mandible as a whole. It also shows a long groove on the upper surface of the symphysis.
When in articulation, the whole skull would have been about 21 cm (about 8 inches) long and about 3.5 cm (about 1.5 inches) tall. It had at least 112 teeth in total, with one tooth emerging every three millimeters. When the mouth was closed, the long needle-like teeth interlaced, with teeth from the opposite jaw filled in the gaps between adjacent teeth. Comparison to other pterosaurs suggests that the wingspan of Pterofiltrus was about 100 cm (40 inches), but without any of the rest of the skeleton other than two vertebrae, this is just a rough estimate.
Jiang and Wang assigned Pterofiltrus to the Ctenochasmatidae, a diverse group of filter-feeding pterosaurs that first emerged in the Late Jurassic and lived as late as the end of the Early Cretaceous. All ctenochasmatids had long narrow snouts with large numbers of needle-shaped teeth, like Pterofiltrus. Ctenochasmatids are part of a larger lineage of pterosaurs known as the archaeopterodactyloids that were the earliest common short-tailed pterosaurs.
Although Jiang and Wang didn’t perform a phylogenetic analysis, they did compare Pterofiltrus to a large number of other ctenochasmatid species including several others from the area. Pterofiltrus has a unique combination of features, including the long mandibular symphysis, the symphysis groove, and a very long upper tooth row extending as far back as the nasoantorbital fenestra.
The Yixian Formation is famous for its feathered dinosaurs, but is also home to many exquisite pterosaur specimens, among thousands of other amazing fossils. One hundred twenty-five million years ago, the environment was a temperate forest with numerous lakes, perfect feeding grounds for Pterofiltrus and its kin.