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| Dearc sgiathanach Jagielska, O’Sullivan, Funston, Butler, Challands, Clark, Fraser, Penny, Ross, Wilkinson & Brusatte, 2022 Illustration: Natalia Jagielska |
Highlights:
• A new pterosaur genus and species from the Middle Jurassic of Scotland is described
• It is represented by a well-preserved fossil skeleton, including the brain endocast
• It was not fully grown when it died and would have had a wingspan of >2.5 m
• Pterosaurs evolved to a considerably larger size earlier than previously recognized
Summary
Pterosaurs were the first vertebrates to evolve flight and include the largest flying animals in Earth history. While some of the last-surviving species were the size of airplanes, pterosaurs were long thought to be restricted to small body sizes (wingspans ca. <1.8–1.6 m) from their Triassic origins through the Jurassic, before increasing in size when derived long-skulled and short-tailed pterodactyloids lived alongside a diversity of birds in the Cretaceous. We report a new spectacularly preserved three-dimensional skeleton from the Middle Jurassic of Scotland, which we assign to a new genus and species: Dearc sgiathanach gen. et sp. nov. Its wingspan is estimated at >2.5 m, and bone histology shows it was a juvenile-subadult still actively growing when it died, making it the largest known Jurassic pterosaur represented by a well-preserved skeleton. A review of fragmentary specimens from the Middle Jurassic of England demonstrates that a diversity of pterosaurs was capable of reaching larger sizes at this time but have hitherto been concealed by a poor fossil record. Phylogenetic analysis places D. sgiathanach in a clade of basal long-tailed non-monofenestratan pterosaurs, in a subclade of larger-bodied species (Angustinaripterini) with elongate skulls convergent in some aspects with pterodactyloids.6 Far from a static prologue to the Cretaceous, the Middle Jurassic was a key interval in pterosaur evolution, in which some non-pterodactyloids diversified and experimented with larger sizes, concurrent with or perhaps earlier than the origin of birds.
Keywords: pterosaur, Jurassic, Scotland, Isle of Skye, wingspan, paleontology, evolution, fossil, histology, phylogeny
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| The new Middle Jurassic pterosaur Dearc sgiathanach (A–C) Photographs of main slab (NMS G.2021.6.1–2), bones in dorsal view (A); wing phalanges 2–3 (NMS G.2021.6.3–4), in dorsal view (B); and main counterslab (NMS G.2021.6.3), bones in ventral view (C). (D–F) Schematic drawings of (A)–(C). (G–H) Reconstruction of skull in dorsal (G) and ventral (I) views and skeleton in lateral view (H). ar, articular region; cd, caudal vertebrae; cor, coracoid; cv, cervical vertebrae; d, digit; den, dentary; dors, dorsal vertebrae; dpc, deltopectoral crest; ep, extensor process; fm, femur; gas, gastralia; hdc, humeral distal condyle; hmt, humeral tubercle; isc, ischium; ju, jugal; max, maxilla; mc, metacarpal; mt, metatarsal; po, postorbital; r, ribs; sac, sacral plate; sca, scapula; scv, sacral (?) vertebrae; sm, sesamoid; sq, squamosal; st, sternum; symp, symphysis; uc, ulnar crest; ul, ulna; wp, wing phalanx; r/l, right/left. Blue on reconstructions are missing regions; red line in (E) is location of histological sectioning. Scale bars, 30 mm. |
Pterosauria Owen, 1842
Breviquartossa Unwin, 2003
Rhamphorhynchidae Seeley, 1870
Rhamphorhynchinae Seeley, 1870
Angustinaripterini He, 1983
Included species: Angustinaripterus longicephalus, Sericipterus wucaiwanensis, and Dearc sgiathanach (below).
Diagnosis: Group of rhamphorhynchine pterosaurs sharing a low and elongate skull (height-to-length ratio < 0.2); large antorbital fenestra (20%–35% skull length and >80% orbit dorsoventral height); lacrimal process of jugal nearly perpendicularly inclined (90°–110°) to jugal body; strongly inclined quadrate (130°–140° relative to maxilla long axis); cervical vertebrae with considerable change in length-to-width ratio across the neck (1.8 to 1.2, from anterior to posterior); humeral diaphysis slender with muscle scar tubercle.
Dearc n. gen.
Dearc sgiathanach sp. nov.
Etymology: Scottish Gaelic, with the double meaning of “winged reptile” and “reptile from Skye,” paying homage to pterosaurs (winged reptiles) and the Gaelic name for Skye (An t-Eilean Sgitheanach, the “winged isle”). Phonetic pronunciation: jark ski-an-ach.
Holotype: NMS (National Museums Scotland, Edinburgh) G.2021.6.1-4, a three-dimensionally preserved articulated skeleton, lacking anterior and dorsal portions of the cranium, left manus, portions of the wings, hindlimb elements, and the distal tail. The fossil was separated into four slabs during preparation: the main slab contains the majority of bones, exposed in dorsal view (NMS G.2021.6.1), and the main counter slab contains bones exposed ventrally (NMS G.2021.6.3). An additional block contains a wing phalanx (NMS G.2021.6.4). The skull and anterior cervical vertebrae (NMS G.2021.6.2) were separated from the main slab for X-ray computed microtomography (μCT) (Figure 2).
Diagnosis: Dearc sgiathanach is a rhamphorhynchine pterosaur with the following autapomorphies: tri-tubular vomers with “trident-shaped” precapillary contact, pre-choana depression on the palatal surface of the maxilla, enlarged optic lobes expanded anteroposteriorly, and fourth metatarsal more robust (diameter 2.5×) than mt1-3.
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| Phylogenetic relationships of the Middle Jurassic pterosaur Dearc sgiathanach and wingspan estimates for Jurassic pterosaurs Strict consensus of most parsimonious trees from phylogenetic analysis, with silhouettes scaled to wingspan (Dearc = ca. 2.0 m) (1), and skull reconstructions of key taxa: (A) Scaphognathus crassirostris (based on GPIB 1304), (B) Dorygnathus banthensis (based on SMNS 55886), (C) Rhamphorhynchus muensteri (based on NHMUK R 37002), (D) Angustinaripterus longicephalus (based on ZDM T8001), and (E) Dearc sgiathanach. Wingspan plot (2): estimated wingspan range for isolated pterosaur remains from the Taynton Limestone collection. (A) NHMUK PV R 36634, (B) GSM 113726, (C) OUM J28352, (D) NHMUK PV R 38016, (E) NHMUK PV R1362, (F) LL12158, (G) NHMUK PV R 40126, (H) NMS G.2021.6.1-4 (Dearc), (I) OUM J23046, (J) OUM J28273, (K) NHM UK PV R 40126 B, (L) OUM J28319, (M) OUM J28307, (N) OUM J28271, (O) OUM J28354, (P) LL12160, (Q) OUM J23047, and (R) MJM L K1995. |
Natalia Jagielska, Michael O’Sullivan, Gregory F. Funston, Ian B. Butler, Thomas J. Challands, Neil D.L. Clark, Nicholas C. Fraser, Amelia Penny, Dugald A. Ross, Mark Wilkinson and Stephen L. Brusatte. 2022. A Skeleton from the Middle Jurassic of Scotland illuminates An Earlier Origin of Large Pterosaurs. Current Biology. DOI: 10.1016/j.cub.2022.01.073
