剪嘴翼龍屬

剪嘴翼龍（屬名：Forfexopterus，意為「剪刀翅膀」）是梳頜翼龍科翼龍的一個屬，化石發現於中國早白堊世九佛堂組。屬下包括單一物種熱河剪嘴翼龍（F. jeholensis），由蔣順興等人於2016年根據一副基本完整的骨骼所命名。第二件標本由一隻翅膀組成，於2020年描述。首件標本尺寸較大，但發育成度弱於第二件標本，表明剪嘴翼龍的發育軌跡是可變的。像其它梳頜翼龍科一樣，剪嘴翼龍生有長而窄的顱骨，口中有眾多細小牙齒，與該類群其它成員不同的是剪嘴翼龍沒有鏟形吻尖或嵴，牙齒也更彎曲。有一項特徵可區分剪嘴翼龍與更廣泛類群古翼手龍下目的所有其它成員，即翼指的四節指骨中，第一節短於第二節但長於第三節。

剪嘴翼龍屬 化石時期：阿普第階，
剪嘴翼龍的第二件標本（SDUST V1003）
科學分類
界：	動物界 Animalia
門：	脊索動物門 Chordata
綱：	蜥形綱 Sauropsida
目：	†翼龍目 Pterosauria
科：	†梳頜翼龍科 Ctenochasmatidae
屬：	†剪嘴翼龍屬 Forfexopterus Jiang et al., 2016
模式種
†熱河剪嘴翼龍 Forfexopterus jeholensis Jiang et al., 2016

發現與命名

剪嘴翼龍正模標本由當地農民所發現，但在去除周圍岩石的過程中部分受損，後來得到清修。標本被編號為HM V20，代表單具個體，由一副基本完整的骨骼組成，其中含有顱骨但缺少大部分脊柱。其發現於中國遼寧省建昌縣喇嘛洞鎮附近肖台子村的九佛堂組岩層中，該層位的地質年齡為大約1.2億年前（阿普第階）。該標本由蔣順興等人於2016年描述。

第二件標本SDUST V1003由周長付等人於2020年描述，由一隻關節連接的右翅組成，發現於肖台子村東北3.5公里（2.2英里）處的小窯溝村。當所有保存下來的骨頭均已出土時，翅膀細長的第四掌骨有兩處斷裂，第二及第三指部分缺失。和正模標本一樣，該標本也是在發挖期間受損，尺骨、橈骨、腕骨及翼狀骨（翼龍翅膀所特有的骨骼）上的某些解剖學特徵亦變得模糊不清。周長付等人於2022年描述了第三件標本SDUST V1007。該標本由下頜吻尖組成，發現於建昌縣大窯溝村。

屬名取自拉丁語forfex（剪刀）及希臘語pterus（翅膀），指其剪刀形的雙顎；種名指熱河省。

描述

剪嘴翼龍標本與人類的體型比較

Forfexopterus would have been large for an archaeopterodactyloid pterosaur. In 2016, Jiang and colleagues estimated the wingspan of HM V20 at 3米（9.8英尺）; in 2020, Zhou and colleagues revised this to 2.37米（7英尺9英寸） by doubling the length of the wing. A similar methodology yielded 1.78米（5英尺10英寸） for SDUST V1003. Despite being the larger specimen, HM V20 was only a subadult, while the smaller SDUST V1003 was an adult. The former has unfused bones that are typically fused in adult pterosaurs: the atlas and axis, the first two neck vertebrae; the scapula and coracoid in the shoulder; the epiphysis (lower end) of the humerus to its shaft; and the attachment of the extensor tendon to the first phalanx bone of the wing finger, whereas these are all fused in the latter. This discrepancy is suggestive of developmental variation in the genus, and may be both connected to and independent of sexual dimorphism as in other pterosaurs such as Pteranodon; however, insufficient fossil evidence exists to assess this.

顱骨與椎骨

The skull was low and long, measuring 51厘米（20英寸） in length. The tip of the upper jaw was not expanded into a spatulate shape, unlike Gnathosaurus, Huanhepterus, and Plataleorhynchus. Unlike Feilongus and Moganopterus, it appears that no crest was present on either jaw. Both jaws were filled by slender, smooth-surfaced teeth that pointed outwards like other ctenochasmatids, with an estimated 30 and 28 teeth on each side of the upper and lower jaws. However, the teeth of Forfexopterus were more curved than other ctenochasmatids, and they were also less dense than contemporary ctenochasmatids (with a tooth density of 2.2厘米（0.87英寸） in the lower jaw). The teeth were restricted to the front third of the jaw, before the nasoantorbital fenestra that housed the nostrils, which was similar to Huanhepterus, Cathayopterus, and Gegepterus. These characteristics are part of a unique combination of features that distinguishes Forfexopterus. While Pterofiltrus had a similar number of teeth, they occupied more of the jaws. The tip of the lower jaw had a short midline projection at the front, which is also seen in Pangupterus and Liaodactylus; a similar process is known as the odontoid process in the Istiodactylidae, but unlike in istiodactylids the process of Forfexopterus was probably too short to have had a cutting function.

In the neck, the axis (second neck vertebra) was short and had a low neural spine on top, like Moganopterus. However, the fifth neck vertebra was less elongated than Moganopterus or Huanhepterus and was closer to the typical condition of other archaeopterodactyloids (being 4.7 times as long as it was wide). Ribs are associated with the fifth neck vertebra as in Beipiaopterus and Gegepterus, but the sixth and seventh lack them. Unlike the Boreopteridae, these vertebrae had relatively low neural spines as well.

四肢及肢帶

Comparison of reconstructed wings of (a) SDUST V1003 and (b) HM V20

In the shoulder girdle, a number of characteristics contributed to a unique combination of features: a pointed projection on the sternum known as the cristospine was long; the location where the coracoids attached to the sternum, located on either side of a midline ridge on the cristospine, was further forward on the right side than the left; and the coracoid bears a weakly-developed flange (also known in Beipiaopterus, Gegepterus, and Elanodactylus, although also variably present in the Azhdarchoidea). HM V20 in particular was the first archaeopterodactyloid specimen that preserved the articulation of the sternum with the coracoid. Like Beipiaopterus, Elanodactylus, and Zhenyuanopterus, the scapula was longer than the coracoid. Unlike Gegepterus, the back of the sternum was curved in Forfexopterus.

In the arm, the humerus had a well-developed deltopectoral crest that was only a quarter of the shaft's length like Beipiaopterus and Zhenyuanopterus. At the bottom of the crest, HM V20 had an opening (pneumatic foramen), also seen in Elanodactylus and Boreopterus, but the condition in SDUST V1003 is unclear. Unlike contemporary archaeopterodactyloids, the ulna was proportionally long compared to the humerus (being 63% longer in HM V20 and 48% longer in SDUST V1003). The ulna was slightly thicker than the radius, like Beipiaopterus and Huanhepterus, while it was up to twice as thick in other archaeopterodactyloids. For the slender, pointed pteroid, the ratio of its length was similar to the Boreopteridae (46.7% in HM V20, 47.3% in SDUST V1003). Forfexopterus is unique among archaeopterodactyloids in that the first phalanx bone of its wing finger was shorter than the second but longer than the third; Elanodactylus was similar, except the first was shorter than the third. The first three wing phalanges were straight, while the fourth phalanx was curved with an expanded (not pointed) end like Elanopterus and Gegepterus. All three of the free digits were tipped with large, curved claws bearing prominent tubercles for muscle attachment, with the first digit being shortest and the third being longest.

As in Elanodactylus and Huanhepterus, the head of the femur had a constricted neck and a flat articulating surface. Like most other archaeopterodactyloids, the tibia was longer than the femur. Relative to Beipiaopterus and Gegepterus, the fibula was short compared to the tibia at 40% of its length, but the third metatarsal bone was similar at 37.1% of its length. Compared to the hand, the claws on the five toes of Forfexopterus were relatively small. Some authors have suggested that the foot structure of Forfexopterus and other filter feeding ctenochasmatids—with long metatarsals and small digits—may have been an adaptation to improve the ability to wade in water.

分類

Jiang and colleagues determined that Forfexopterus was a member of the Archaeopterodactyloidea, on account of the long fourth (wing) metacarpal and the reduced fifth metatarsal in the foot. They tentatively assigned it to the Ctenochasmatidae based on the long snout, the presence of more than 100 teeth, the third metatarsal of the foot being longer than a third of the tibia, and the presence of projections called exapophyses on the vertebrae. This attribution was followed by Zhou and colleagues, as well as other authors in their assessments of ctenochasmatid specimens. In 2023, Jiang and colleagues noted proportional similarities between Forfexopterus, Elanodactylus, Eosipterus, and their new taxon Cratonopterus, which they used to affirm its position within the Ctenochasmatidae. Pêgas (2024) included Forfexopterus in a phylogenetic analysis of the Pterosauria and found support for similar relationships, with Forfexopterus and Elanodactylus as sister taxa within the Ctenochasmatoidea. These results are displayed in the cladogram below:

	Aurorazhdarcho       Ardeadactylus     Huanhepterus             Elanodactylus     Forfexopterus         Gladocephaloideus       Feilongus     Moganopterus                 Liaodactylus       Pterofiltrus     Cathayopterus             Plataleorhynchus       Lusognathus       Gnathosaurus     Tacuadactylus             Ctenochasma spp.       Pterodaustro       Gegepterus     Beipiaopterus

古生物學

牙齒磨損與替換

Illustration of the Forfexopterus holotype skull fossil material and reconstructed skull

The teeth of the Forfexopterus lower jaw specimen SDUST V1007 showed signs of abrasion near the tip of the crown, with the teeth having wear facets on the outer (labial), inner (lingual), or both surfaces. The facets on the outer surfaces tended to be relatively low-angled, and were only present on more heavily-worn teeth. By contrast, the facets on the inner surfaces were higher-angled and were present on most of the teeth, implying that this type of tooth abrasion began earlier in life. Such wear facets arise from regular contact (occlusion) between teeth in the upper and lower jaws. However, this contact only results in facets on the outer surfaces of the lower teeth and on the inner surfaces of the upper teeth.

In 2022, Zhou and colleagues suggested that the unique wear pattern of SDUST V1007 was related to the pattern of tooth replacement in Forfexopterus. This specimen preserves nine replacement teeth on the lower jaw, which were sharp and pointed. They grew on the insides of the functional teeth to about a third of their length. If a similar pattern of tooth replacement existed in the upper jaw, this would suggest that the wear facets on the inner surfaces of the lower teeth were made by the older functional tooth, while the wear facets on the outer surfaces of the lower teeth were made by their replacement teeth. Zhou and colleagues indicated that this pattern could only occur when the teeth pointed outwards horizontally, as was the case in Forfexopterus and other ctenochasmatids.

Ctenochasmatid teeth vary in shape and arrangement, from the needle-like, closely-packed teeth of Pterodaustro and Ctenochasma (adapted for eating planktonic prey) to the wider-spaced teeth of Gnathosaurus and Plataleorhynchus arranged in spoonbills (adapted for eating larger prey). Biomechanical research indicates that these specialized forms had very weak bite forces. Compared to these forms, Forfexopterus, Feilongus, and Moganopterus had short tooth rows and widely-spaced teeth, but also lacked spoonbill-shaped snouts. Combined with the wear facets of Forfexopterus, Zhou and colleagues suggested that this was indicative of a relatively active feeding strategy.

古生態學

主條目：九佛堂組

Holotype specimen of Ikrandraco, a contemporary of Forfexopterus

The Jiufotang Formation in the Lamadong area consists of lake deposits, with at least SDUST V1003 having been discovered in such deposits. In particular, fish similar to Jinanichthys and freshwater snails similar to Galba were found on the same slab as SDUST V1003. Other pterosaurs from these deposits include the ctenochasmatid Moganopterus, the lonchodectid Ikrandraco, and the anurognathid Vesperopterylus. Pterosaurs known from other deposits of the Jiufotang Formation include the ctenochasmatids Feilongus, Gladocephaloideus, and Pangupterus; the anhanguerians Guidraco, Liaoningopterus, and Linlongopterus; the chaoyangopterids Chaoyangopterus, Eoazhdarcho, Jidapterus, and Shenzhoupterus; the istiodactylids Istiodactylus, Liaoxipterus, Lingyuanopterus, Nurhachius, and possibly Hongshanopterus; and the tapejarid Sinopterus, for a total of 23 pterosaur species from the formation as of 2016.

Other animals known from the same beds as Forfexopterus include the ornithuromorph birds Mengciusornis and Zhongjianornis; the enantiornithine birds Fortunguavis and Bohaiornis; the turtles Liaochelys and Perochelys; the lizard Yabeinosaurus; the choristoderan Philydrosaurus; the mammal Liaoconodon, and the cynodont Fossiomanus.