Liaodactylus
Liaodactylus is a genus of filter-feeding ctenochasmatid pterosaur from the Jurassic of China. The genus contains one species, L. primus, described by Zhou et al. in 2017. As an adaptation to filter-feeding, Liaodactylus had approximately 150 long, comb-like teeth packed closely together. It is both the earliest known ctenochasmatid and the first filter-feeding pterosaur from the Jurassic Tiaojishan Formation. Later and more specialized ctenochasmatids differ from Liaodactylus in having longer snouts, smaller openings (or fenestrae) in the skull, and more teeth. Within the Ctenochasmatidae, Liaodactylus was most closely related to the European Ctenochasma.
There is one specimen of Liaodactylus known, namely the holotype PMOL-AP00031, which is stored at the Palaeontological Museum of Liaoning. It consists of a complete skull and lower jaws, along with the first two cervical vertebrae. It originates from outcrops located about 500 metres (1,600 ft) west of the village of Daxishan, in Jianchang County, Liaoning, China. These outcrops belong to the Late Jurassic Tiaojishan Formation, which has been dated to range from 161.8 ± 0.4 to 159.5 ± 0.6 million years ago (Oxfordian) based on argon-argon dating.[1][2][3]
Liaodactylus was described in 2017 by Zhou et al. The genus name combines Liao, a shortened prefix form of "Liaoning", with Greek dactylos ("finger"), a standard pterosaurian suffix. Meanwhile, the specific name primus, from Latin, refers to the early age of Liaodactylus relative to other ctenochasmatids.[1]
The head of Liaodactylus is slender and long, with a skull length of 13.3 centimetres (5.2 in) and a jaw length of 11.7 centimetres (4.6 in).[1] Out of this, the snout is 49.1% of total skull length, and the nasoantorbital fenestra (the fusion of the nostril and the antorbital fenestra, seen in all members of the Monofenestrata[4][5]) is 31% of skull length. In more derived ctenochasmatids, the nasoantorbital fenestra is much smaller relative to the skull, being only 10-12% of skull length in Pterodaustro; the snout is also longer, being over 85% of skull length in Pterodaustro.[6] Also shorter than other ctenochasmatids is the dentary symphysis, the fused portion of the lower jaw, which is only 30.5% of jaw length. Morphologically, the sides of the snout are parallel (unlike the spoon-tipped snouts of Gnathosaurus), most of the mandible is composed mainly of the dentary, and the well-developed retroarticular process is formed by the angular bone like in other ctenochasmatids.[1]
There are many long, needle-like, outward-projecting, tightly packed, equally-spaced teeth in the jaws of Liaodactylus, totalling to 152 teeth across both jaws. This is more than Gnathosaurus (128–136), about the same as Gegepterus (150),[7] but much less than Ctenochasma (200-552)[8] and Pterodaustro (almost a thousand).[6] The teeth become shorter towards the back of the jaws, eventually becoming short, peg-like structures at the back of the tooth row; the back of the tooth row corresponding to the front 1/3 of the nasoantorbital fenestra, which is unusual among ctenochasmatids (where the teeth usually stop entirely before the fenestra). The first tooth at the front of each jaw is also somewhat shortened, being only half the length of the second. Collectively, the teeth, which would have interlocked when the jaw was closed, form a comb-like complex that would have been used for filter-feeding.[1][9]
