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 discovered in 2006 and named in 2024. It is the only pterosaur from the Kilmaluag Formation and the second pterosaur named from Scotland, after Dearc in 2022. As one of the few pterosaur skeletons known from the Middle Jurassic, its discovery contributed to understanding the early diversification of the group. Belonging to Darwinoptera, a clade intermediate between early rhamphorhynchoid and later pterodactyloid pterosaurs, it would have been a small animal with a large head and long tail. It is distinguished from all other pterosaurs by two traits: the large size of a wavy flange on its coracoid and a prominent depression on the back extension of the ilium. It would have lived in a low-salinity lagoon ecosystem with wet and dry seasons.

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 discovered in 2006 and named in 2024. It is the only pterosaur from the Kilmaluag Formation and the second pterosaur named from Scotland, after Dearc in 2022. As one of the few pterosaur skeletons known from the Middle Jurassic, its discovery contributed to understanding the early diversification of the group. Belonging to Darwinoptera, a clade intermediate between early rhamphorhynchoid and later pterodactyloid pterosaurs, it would have been a small animal with a large head and long tail. It is distinguished from all other pterosaurs by two traits: the large size of a wavy flange on its coracoid and a prominent depression on the back extension of the ilium. It would have lived in a low-salinity lagoon ecosystem with wet and dry seasons.

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 insertion 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 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 shorter and more robust than the slender, elongate processes found in Kunpengopterus and other darwinopterans.

Comparative anatomy

; Ceoptera would have looked very similar 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 darwinopterans 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 to 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, rounded prominences 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 vertebrae 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 present 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 constricted, 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 underside 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.

Palaeoecology

dinosaurs that lived alongside Ceoptera 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, the formation 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, expanding and drying 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. , pictured, demonstrate ecological ties to the Forest Marble Formation. A rich fauna is preserved at Cladach a'Ghlinne and other sites within the formation. This fauna is similar 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. Insect 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 found in the formation include Bellairsia gracilis, Balnealacerta, and Parviraptor. 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 neornithischian 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.

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