Ceoptera

''Ceoptera'' (meaning "mist wing") is an extinct genus of darwinopteran pterosaur from the Middle Jurassic Kilmaluag Formation of Scotland. The genus contains a single species, ''C. evansae'', known from a partial skeleton. It is the only pterosaur from Kilmaluag Formation. ''Ceoptera'' represents the second pterosaur named from Scotland, after '' Dearc'' in 2022.

Discovery and naming

In 2006, a set of rocks with protruding fossilized bones was noticed by a team of palaeontologists on Cladach a’Ghlinne, a beach north of Elgol on the Isle of Skye in Scotland. Fossils of this site are considered to be part of the Kilmaluag Formation, dated to the Middle Jurassic. The site was administered by the Scottish Natural Heritage as a Site of Special Scientific Interest, disallowing the disturbance of rocks on the clifface, and the land was owned by a private trust. However, permission was granted by both parties for collection of the specimen as it had fallen naturally onto the beach. Care was taken in returning the specimen to the Natural History Museum in London, England as it was very fragile. Preparation, the process of removing the fossils from the surrounding rock (the matrix), proved difficult. The limestone matrix was especially hard, fossils within were very fragile; twelve months of acid preparation were necessary. Many remains were still embedded in the rock after this point, and CT scanning was necessary to visualize and study them.

The discovery was considered significant, as pterosaur fossils from the Middle Jurassic are extremely rare. Most of the knowledge on pterosaurs comes from specimens preserved in lagerstätten sites, which have an exceptional capacity for preservation, localized within the Late Jurassic and Early Cretaceous. Contrastingly, there is a paucity remains from other points in time, especially the Early and Middle Jurassic, a critical point in pterosaur evolution. As only the fourth Middle Jurassic pterosaur known from an associated skeleton rather than an individual bone, the Kilmalaug specimen was considered to be important to pterosaur research. Additionally, it is the most complete pterosaur found in the United Kingdom since ''Dimorphodon'' was discovered by Mary Anning in the early 1800s. The specimen, catalogued as NHMUK PV R37110, is preserved on three blocks, and consists of four torso vertebrae, a single tail vertebra, two other poorly preserved vertebrae of uncertain position, fragments of the sternum and pelvis, a complete scapulocoracoid, and several bones from the left forelimb and hindlimb.

The fossil material was first mentioned in a 2019 conference abstract, later in a 2020 review of the fossil vertebrae fauna of the Kilmaluag Formation, and in a 2022 academic preprint. In 2024, Elizabeth Martin-Silverstone and her colleagues described the specimen as the new genus and species ''Ceoptera evansae'' in a study published in the ''Journal of Vertebrate Paleontology''. The generic name, "''Ceoptera''", combines the Scottish Gaelic word "cheò"/"ceò" (pronounced "ki-yo"), referencing the common Gaelic name for the Isle of Skye, Eilean a' Cheò (meaning "Isle of Mist"), and the Latin word "ptera", meaning "wing". The specific name, "''evansae''", honours British paleontologist Susan E. Evans, honouring her scientific contributions as well her role in introducing the team to the Skye locality and facilitating the discovery. It is only the second pterosaur named from Scotland, after '' Dearc'' in 2022.

Description

The ''Ceoptera'' holotype has an estimated forelimb length of and wingspan of around . Many skeletal structures are fully fused, and some surfaces of the bones have a dense, smooth texture. Both of these features are characteristic of osteological maturity, so the individual was likely done growing when it died. As a darwinopteran, ''Ceoptera'' would have likely possessed a long head, bearing many small pointed teeth and a prominent cranial crest. Its neck would have relatively long, compared to early pterosaurs, with prominent wings and a long, stiff tail.

Distinguishing traits

Compared to all other pterosaurs, ''Ceoptera'' is distinguished by two unique traits. The first is found in the coracoid, a shoulder bone that articulates with the sternum. In most pterosaurs, the bottom of the coracoid has a small flange on its inner edge, and in darwinopterans a similar flange is expanded on the outer edge as well, in a triangular shape. In ''Ceoptera'', this flange is especially expanded, extending along a quarter of the coracoid and possessing a nearly rectangular shape. A similarly shaped elongate flange is present in ''Kunpengopterus'', but that of ''Ceoptera'' ends more abruptly and has a unique wavy margin. This flange was interpreted as a likely site for the intersection of the ''m. sternocoracoideus'' muscle. The second distinguishing trait is found on the ilium, part of the pelvis. The post-acetabular process, an elongate portion of bone sticking backwards from the ilium beyond the hip socket, is overall similar in anatomy to other darwinopterans. However, the outward-facing side of the process has is recessed in shape, with a small vertical ridge splitting this depression into two equal halves. In almost all other pterosaurs, this side of the bone has a flat or convex shape. ''Kunpengopterus'' also has a depression, but it is small in size by comparison. Additionally, the process as a whole is more short and robust than the slender, elongate processes found in ''Kunpengopterus'' and other darwinopterans.

Comparative anatomy

The anatomy of the forelimb is rather typical of a darwinopteran. The cristospine of the sternum, a bony crest unique to pterosaurs, is short, deep, and robust as in other darwniopterans but unlike other pterosaurs. The ulna and radius are entirely typical of Jurassic pterosaurs, and the syncarpals (fused carpal bones of the wrist) have a roughly pentagonal outline similar those of ''Kunpengopterus'' and unlike the rectangular form in more primitive taxa. The metacarpal of the fourth finger is, like those of other darwinopterans, intermediate in length between the short finger of earlier pterosaurs and the long ones of later pterodactyloid ones. Both condyles, attachment points at the end of the bone, project outwards so as to form a sloping shape shared with other monofenestratan pterosaurs and unlike the flat, parallel shape seen in earlier forms like ''Rhamphorhynchus''. Unusually, a notch on the upper surface of the finger's midsection that accommodates the fully flexed wing finger in other pterosaurs is absent, as is a muscle scar usually present in an adjacent position. The preserved finger bone of the wing is entirely ordinary for a pterosaur.

Few vertebra are preserved, but illustrate anatomy from various portions. A well preserved vertebra from the front of the torso has an overall typical shape for a small pterosaur. The portion of the transverse processes (long projections on either side of the vertebra) that attaches to the capitular facets (an attachment point for the ribs) extend forward onto the side of the prezygapophyses (articulations points for the preceding vertebra). Additionally, this same portion of the process extends beyond the capitular facet to form a short flange. Both of these extensions of the transverse process are absent in most pterosaurs, but they are presented in the related ''Darwinopterus''. A similar extension of the transverse process onto the prezygapophyses is seen on a vertebra preserved from the back of the torso. The known vertebra from the front of the tail is typical, with a long shape and simplistic anatomy. Developed processes pointing forward and backward from the attachment points for adjacent vertebrae indicate the presence of elongate filiform processes extending along the tail, typical of many long-tailed pterosaurs.

The hindlimb of ''Ceoptera'' is, likewise, similar to its relatives. Most of the femur is similar to other pterosaurs; the upper portion has a well developed greater trochanter projecting upwards, unlike more primitive pterosaurs but similar to darwinopterans. The femoral neck is elongate and constrict, distinct from the typical short and stout neck seen in the femurs of other darwinopterans. The tibia and fibula are, contrastingly, similar to those of other darwinopterans in every respect. The one preserved foot claw is elongate, with a recurved shape. The flexor tubercle, a portion of the unside of the claw allowing it to be flexed, has a geometric (rather than round) shape and a flat bottom edge that gently slopes into the main portion of the claw. This anatomy is not unique to ''Ceoptera'', but is distinctive of Darwinoptera and distinct from other pterosaurs.

Classification

Martin-Silverstone et al. (2024) recovered ''Ceoptera'' as a darwinopteran member of the Monofenestrata, in an unresolved polytomy with similar taxa. The Darwinoptera is, in turn, the sister taxon to the Pterodactyloidea.

Palaeoecology

Known remains of ''Ceoptera'' are found in the Kilmaluag Formation, part of the Great Estuarine Group and dating to the Bathonian age of the Jurassic period, around 166.1 million years ago. Specifically, ''Ceoptera'' is found in the vertebrate beds of the southern, argillaceous mud and limestone dominated section of the formation. During the Bathonian, it would have represented a freshwater or low-salinity closed lagoon ecosystem near the ocean fed by meteoric waters, with sediments delivered by surrounding rivers. The lagoon would have been shallow, and expanded and dried out with the passage of wet and dry seasons. During these dry periods, mudflats would have been exposed. The preservation of vertebrate fossils in these beds is characterized by a distinct black colour, as seen in ''Ceoptera''. This ecosystem is distinct from that found in other sections of the Great Estuarine Group, which are saltwater in nature. As represented in a higher layer, the lagoon would eventually more permanently dry out into an exposed supralittoral ecosystem which was significantly more barren than the vertebrate beds.

A rich fauna is preserved at Cladach a’Ghlinne and other sites within the formation. This fauna is noted for its similarity to that of the Forest Marble Formation, a formation of similar age found in England. Plant fossils, contrastingly, are extremely rare within the Kilmaluag Formation, mostly restricted to gymnosperm pollen and pteridophyte spores. Invertebrates are best represented by extremely abundant freshwater ostracods such as ''Darwinula'' and '' Theriosynoecum''. Other invertebrates include conchostracans '' Anthronesteria'' and '' Pseudograpta'', the gastropod ''Viviparus'', and the bivalve '' Unio''. Burrows indicate the presence of shrimps or crabs. Insects fossils are not common, but include beetles. Fish include the hybodonts ''Acrodus'' and ''Hybodus'', pycnodonts, the semionotiform ''Lepidotes'', amiiforms, and a sarcopterygian that may be a type of coelacanth. Amphibians include the karaurid '' Marmorerpeton wakei'', a very primitive form of salamander, as well as the albanerpetontid ''Anoualerpeton''; frogs are seemingly absent.

Many reptiles are found in the formation, with the early lepidosauromorph ''Marmoretta'' being the most common. Lizards include '' Bellairsia gracilis'', '' Balnealacerta'', and '' Parviraptor'' are also found in the formation. Rhynchocephalians appear to be absent. Aquatic reptiles include the choristodere ''Cteniogenys'', and turtle remains are common, including '' Eileanchelys'', one of the earliest aquatic turtles. Crocodylomorphs are represented by atoposaurids and goniopholids. Dinosaurs are primarily known from tracks, indicating the presence of megalosaurid theropods and large eusauropods. A neornithischiann dinosaur, possibly the oldest known ornithopod, is represented by a partial skeleton. Mammals include the tritylodontid '' Stereognathus ooliticus'', the docodonts ''Borealestes serendipitus'', '' Borealestes cuillinensis'', and '' Krusatodon kirtlingtonensis'', the morganucodont '' Wareolestes rex'', the cladotherian '' Palaeoxonodon ooliticus'', and ''Phascolotherium''. Multituberculates and haramiyidans notably appear absent.

References

{{Taxonbar, from=Q124434036

Monofenestrata
Middle Jurassic pterosaurs
Jurassic pterosaurs of Europe
Fossils of Scotland
Jurassic Scotland
Bathonian life
Fossil taxa described in 2024