Forfexopterus
Forfexopterus | |
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Second specimen of F. jeholensis SDUST V1003 | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Order: | †Pterosauria |
Suborder: | †Pterodactyloidea |
Family: | †Ctenochasmatidae |
Genus: | †Forfexopterus Jiang et al., 2016 |
Species: | †F. jeholensis
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Binomial name | |
†Forfexopterus jeholensis Jiang et al., 2016
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Forfexopterus (meaning "scissor wings") is a genus of
Discovery and naming
The holotype specimen of Forfexopterus was discovered by a local farmer, who had partially damaged this specimen while attempting to remove the encasing rock; the specimen was later restored. The specimen, which has the number HM (Hami Museum) V20, represents a single individual, and consists of a mostly complete skeleton including the skull but missing most of the vertebral column.[1] It was discovered in rocks belonging to the Jiufotang Formation, dating to approximately 120 million years ago (the Aptian age), in the Xiaotaizi locality near Lamadong Town, Jianchang County, Liaoning, China.[2][3] It was described in 2016 by Shunxing Jiang and colleagues.[1]
In 2020, the second specimen SDUST (
The generic name Forfexopterus is derived from Latin forfex ("scissors") and Greek pterus ("wings"), and refers to the scissor-like shape of the jaws; the specific name jeholensis refers to the
Description
Forfexopterus would have been large for an
Skull and vertebrae
The skull was low and long, measuring 51 centimetres (20 in) in length. The tip of the upper jaw was not expanded into a spatulate shape, unlike Gnathosaurus, Huanhepterus, and Plataleorhynchus.[6] 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 per centimetre (5.6/in) 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.[1] 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.[4]
In the neck, the axis (second neck vertebra) was short and had a low
Limbs and limb girdles
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[3]). 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.[1]
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.[1][3]
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.[1]
Classification
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.[1] This attribution was followed by Zhou and colleagues.[3]
Palaeobiology
Tooth wear and replacement
The teeth of the Forfexopterus lower jaw specimen SDUST V1007 showed signs of
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.[4]
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.[7] 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.[4]
Palaeoecology
The Jiufotang Formation in the Lamadong area consists of lake deposits,
Other animals known from the same beds as Forfexopterus include the
References
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- ^ Wu, Z.; Gao, F.; Pan, Y.; Wang, X. (2018). "Division and correlation of the Jiufotang Formation and their rare fossil-bearing beds in western Liaoning, China". Geoscience. 32: 758–765.
- ^ .
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- ^ PMC 6754973.
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