Meet Dearc sgiathanach

 

Dearc sgiathanach. Scale bars: 30 mm. Adapted from From Jagielska et al., 2022.

Pterosaurs were the first vertebrates to evolve powerful flight. Their reign extended to every continent and achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. The oldest-known pterosaurs appear in the fossil record about 219 million years ago. Most Triassic and Jurassic pterosaurs are small but already had a highly specialized body plan linked to their ability to fly: shoulder girdle with strongly posteroventrally enlarged coracoid braced with the sternum and laterally facing glenoid fossa; forelimb with pteroid bone and hypertrophied fourth digit supporting a membranous wing; and pelvic girdle with prepubic bone and strongly developed preacetabular process. Pterosaurs have traditionally been divided into two major groups, “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail. Dearc sgiathanach, a newly described rhamphorhynchine pterosaur from the Isle of Skye, Scotland, is the largest known Jurassic pterosaur.

Postcranial skeleton and dentition of Dearc sgiathanach. From Jagielska et al., 2022

Discovered in 2017 by Amelia Penny, the holotype (NMS G.2021.6.1-4), a well preserved, articulated, skeleton, was found at Rubha nam Brathairean (Brothers’ Point), Isle of Skye, in north-west Scotland, in the Lonfearn Member of the Lealt Shale Formation (Bathonian, Middle Jurassic). The specimen is almost complete with the exception of the anterior and dorsal portions of the cranium, the end of the tail, hindlimbs elements, and parts of the wings. The name comes from the Scottish Gaelic language and has a double meaning: “winged reptile” and “reptile from Skye.”

Dearc sgiathanach includes the following autopomorphies: vomers with “trident-shaped” precapillary contact, a pre-choana depression on the palatal surface of the maxilla, and enlarged optic lobes. Bone histology indicates that the specimen belong to a juvenile individual. Based on the proportions of humerus length and skull length of Rhamphorhynchus and Dorygnathus, the research team lead by Natalia Jagielska, estimated the wingspan of Dearc sgiathanach at >2.5 m. Phylogenetic analysys places Dearc sgiathanach within the clade Angustinaripterini. The new specimen suggests that many “pterodactyloid” features convergently evolved in other groups, and hightlights that the Middle Jurassic was a time of increasing diversification in pterosaur history.

References:

JAGIELSKA, Natalia, et al. A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs. Current Biology, 2022. DOI: 10.1016/j.cub.2022.01.073
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