Dearc

Credit: Natalia Jagielska.

*Dearc*, referred to by the working nickname "Scottie", is an extinct genus of augustinaripterinin rhamphorhynchid that lived on the Island of Skye during the Middle Jurassic.

## History

NMS G.2021.6.1-4, the holotype, was discovered in 2017 by Amelia Penny from the east coast of the Trotternish peninsula of the Lealt Shale Formation, being a full 3D articulated skeleton split into four slabs for preparation. Penny had seen the skull poking from the surrounding beach, excavating the specimen with diamond-tipped saws before the tide could fully erode the fossil. As they excavated the concrete-like rock, they found a full skeleton, returning at midnight to continue work. They then left it overnight and returned in the morning to roll the 400-pound slab up the hill and back to a museum. The specimen preserves the body except for the end of the tail (which is cut off by a calcite vein), most of the hindlimb, parts of the wing and the very tip of the beak. Nigel Larkin prepared the specimen to be displayed by National Museums Scotland. *Dearc* comes from the Scottish Gaelic, meaning "Isle of Skye reptile" or "winged reptile", named by Jagielska et al. (2022), but the name was coined by local excavator Dugie Ross. After discovery, *Dearc* made headlines worldwide based on size and completeness, and because it was one of the best preserved pterosaurs from Britain in centuries. The discovery was teased on February 21, 2022 and the paper was published the next day at 10 am GMT.

## Description

It bears features typical of adults related to *Rhamphorynchus*, including large recurved premaxilla teeth, a well-developed crest on the humerus, the scapula and coracoid fusing, smooth bone texture and others. However, the unfused cranial and sacral vertebrae bones indicate immaturity, with histology further supporting that the individual was at least 2 years old at death; this would have made it actively growing. Two prominent growth lines on the wings suggest it died after emerging from a growth hiatus. Because it was immature, a full wingspan could not be obtained, and several phalanges are also missing of the wing finger, which makes estimation difficult. However, they compared more complete taxa, *Rhamphorynchus* and *Dorygnathus*, to find a wingspan of 2.2 meters (based on humerus length) and 3.8 (based on humeral length) of the former. Of the latter, cranial length finds a wingspan of 1.9 meters and humeral length with 1.9 meters. This would make it already the largest Jurassic pterosaur. The estimations based on *Rhamphorynchus* were favoured because it is better sampled, has a fuller ontogenetic series and phylogenetic proximity. Thus, a wingspan of 3 meters is possible.

The bauplan is typical for rhamphorhynchids, but features more similar to pterodactyloids include a skull longer than the dorsals and sacrals combined and cervical shorter than pterodactyloids but more elongate than non-monofenestrians, resembling the more derived *Wukongopterus*. Elongate fangs to the tip of the snout and conical peg-like teeth back are found in the jaws. Autapomorphies include: vomers with 3 tubes that form a trident, the contribution of the maxilla to the palate, a depression in the inner nostril in front of the choana, enlarged optic lobes lengthwise-expanded and a more robust (~2.5 times as thick) fourth metatarsal in the foot. Traits that are not unique but with unique combinations are: a pear-shaped infratemporal fenestra with a narrowing on top and an upward-projecting process in the ectopterygoid that runs through the choana and contacts the vomer perpendicularly.

## Paleobiology

*Dearc* had large fanged teeth near the front of the jaws, with smaller teeth near the back, which in *Rhamphorynchus* are inferred to have functioned similar to a gharial, eating fish and cephalopods. Natalia Jagielska notes that while *Dearc* is the most complete. other large pterosaur fossils are known from the Jurassic, most known only from a single bone. The wing finger phalanges and dorsum were lost via tidal erosion. Preserved are ear canals and a massive optic lobes that correlate to good sight, despite the rest of the brain being tiny and bird-like.

## Classification

Jagielska et al. (2022) recover the following, using then-recent and new publications and research, and excluding taxa known from juveniles and ones that greatly vary with age:

## Paleoecology

*Dearc* is known from the Lealt Shale Formation, a Middle Jurassic of Scotland comprised of silty fissile mudstones with subordinate thin limestones. In this formation, ornithopod, stegosaur and theropod tracks are known alongside a theropod tooth. This was a warm and wet environment riddled with a series of scattered landmasses with shallow water that would have periodically fallen. The theropod, stegosaur and ornithopod tracks were found just meters from *Dearc*. NMS G.2021.6.1-4 is a rare specimen because pterosaur remains are fragile and are not often preserved with such completeness and little distortion/flattening.

## References

1. ↑ https://twitter.com/WryCritic/status/1496716368405803008
2. ↑ https://twitter.com/WryCritic/status/1503823948676538370
3. ↑ 3.0 3.1 3.2 https://www.cell.com/current-biology/fulltext/S0960-9822(22)00135-X#secsectitle0020
4. ↑ https://twitter.com/SteveBrusatte/status/1496062714065657866
5. ↑ https://www.cell.com/current-biology/fulltext/S0960-9822(22)00135-X?\_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS096098222200135X%3Fshowall%3Dtrue
6. ↑ https://www.nationalgeographic.com/science/article/stunning-scottish-pterosaur-is-biggest-fossil-of-its-kind
7. ↑ https://www.scotsman.com/whats-on/arts-and-entertainment/worlds-biggest-jurassic-era-pterodactyl-discovered-on-isle-of-skye-3580073
8. ↑ https://twitter.com/WryCritic/status/1496459727202574342
9. ↑ 9.0 9.1 9.2 https://twitter.com/WryCritic/status/1496062214079279106
10. ↑ https://twitter.com/WryCritic/status/1495867777839775746/photo/1
11. ↑ https://twitter.com/SteveBrusatte/status/1495803631488090115/photo/1
12. ↑ https://twitter.com/WryCritic/status/1496872098685685763
13. ↑ https://en.wikipedia.org/wiki/Rhamphorhynchus
14. ↑ https://twitter.com/WryCritic/status/1496724702911512577
15. ↑ https://en.wikipedia.org/wiki/Lealt\_Shale