| Ceoptera | |
|---|---|
 | |
| Holotype ofCeoptera | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Pterosauria |
| Clade: | †Darwinoptera |
| Genus: | †Ceoptera Martin-Silverstone et al.,2024 |
| Type species | |
| †Ceoptera evansae Martin-Silverstone et al., 2024 | |
Ceoptera (meaning "mist wing") is anextinct genus ofdarwinopteran pterosaur from theMiddle JurassicKilmaluag Formation of Scotland. The genus contains asingle 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, afterDearc in 2022. As one of the only pterosaur skeletons known from the Middle Jurassic, its discovery contributed to understanding the early diversification of the group. Belonging to the group Darwinoptera, a group intermediate between earlyrhamphorhynchoid and laterpterodactyloid 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 itscoracoid and a prominent depression on the back extension of theilium. It would have lived in alow-salinity lagoon ecosystem with wet and dry seasons.
In 2006, a set of rocks with protruding fossilized bones was noticed by a team ofpalaeontologists on Cladach a'Ghlinne, a beach north ofElgol on theIsle of Skye inScotland. Fossils of this site are considered to be part of theKilmaluag Formation, dated to theMiddle 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 theNatural History Museum inLondon,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, andCT scanning was necessary to visualize and study them.[1][2]
Most knowledge about pterosaurs comes from specimens preserved inlagerstätten sites, which have an exceptional capacity for preservation, localized within theLate Jurassic andEarly Cretaceous. Contrastingly, there is a paucity remains from other points in time, especially theEarly and Middle Jurassic, a critical point in pterosaur evolution. The Kilmaluag specimen, laterCeoptera, was only the fourth Middle Jurassic pterosaur known from an associated skeleton rather than an individual bone.[1] Additionally, it is the most complete pterosaur found in theUnited Kingdom sinceDimorphodon was discovered byMary Anning in the early 1800s.[3] The specimen, catalogued asNHMUK PV R37110, is preserved on three blocks, and consists of fourtorso vertebrae, a singletail vertebra, two other poorly preserved vertebrae of uncertain position, fragments of thesternum andpelvis, a completescapulocoracoid, and several bones from the left forelimb and hindlimb.[1]
The fossil material was first mentioned in a 2019conference abstract,[4] later in a 2020 review of the fossil vertebrae fauna of the Kilmaluag Formation,[5] and in a 2022 academicpreprint.[6] In 2024, Elizabeth Martin-Silverstone and her colleaguesdescribed the specimen as the new genus and speciesCeoptera evansae in a study published in theJournal of Vertebrate Paleontology. Thegeneric name, "Ceoptera", combines theScottish 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 theLatin word "ptera", meaning "wing". Thespecific name, "evansae", honours British paleontologistSusan E. Evans for 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, afterDearc in 2022.[1]
TheCeoptera holotype has an estimated forelimb length of 0.76 metres (2 ft 6 in) and wingspan of around 1.6 metres (5.2 ft). 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.[1] As a darwinopteran,Ceoptera would likely have had a long head bearing many small pointed teeth and a prominent cranial crest. Its neck would have been relatively long compared to early pterosaurs, with prominent wings and a long, stiff tail.[7]
Compared to all other pterosaurs,Ceoptera is distinguished by two unique traits. The first is found in thecoracoid, a shoulder bone that articulates with thesternum. 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. InCeoptera, 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 inKunpengopterus, but that ofCeoptera ends more abruptly and has a unique wavy margin. This flange was interpreted as a likely site for the intersection of them. sternocoracoideus muscle. The second distinguishing trait is found on theilium, part of thepelvis. 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 inKunpengopterus and other darwinopterans.[1]
The anatomy of the forelimb is rather typical of a darwinopteran. The cristospine of thesternum, a bony crest unique to pterosaurs, is short, deep, and robust as in other darwinopterans but unlike other pterosaurs. Theulna andradius are entirely typical of Jurassic pterosaurs, and the syncarpals (fusedcarpal bones of the wrist) have a roughly pentagonal outline similar those ofKunpengopterus and unlike the rectangular form in more primitivetaxa. Themetacarpal 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 laterpterodactyloid ones. Bothcondyles, rounded prominences at the end of the bone, project outwards so as to form a sloping shape shared with othermonofenestratan pterosaurs and unlike the flat, parallel shape seen in earlier forms likeRhamphorhynchus. 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.[1]
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 thetransverse 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 theprezygapophyses (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 relatedDarwinopterus. 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 elongatefiliform processes extending along the tail, typical of many long-tailed pterosaurs.[1]
The hindlimb ofCeoptera is, likewise, similar to its relatives. Most of thefemur is similar to other pterosaurs; the upper portion has a well developedgreater trochanter projecting upwards, unlike more primitive pterosaurs but similar to darwinopterans. Thefemoral neck is elongate and constrict, distinct from the typical short and stout neck seen in the femurs of other darwinopterans. Thetibia andfibula are, contrastingly, similar to those of other darwinopterans in every respect. The one preserved foot claw is elongate, with a recurved shape. The flexortubercle, 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 toCeoptera, but is distinctive of Darwinoptera and distinct from other pterosaurs.[1]
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The 2024 study namingCeoptera performed aphylogenetic analysis in order to test its relationships to other pterosaurs, using a dataset built upon those of various prior studies. This analysis found it to belong to the groupDarwinoptera, though this grouping was only weakly supported. Nonetheless, its identity as a darwinopteran was considered to be strongly supported due to the strong resemblance of its skeletal anatomy to other members of that group in several respects, such as the bulbous tip of thescapula and proportions of themetacarpals in the wing. Internal relationships within Darwinoptera were not resolved, but morphological diversity within the group was considered evidence for the existence of various subgroups that remain presently unrecognized. The discovery ofCeoptera and other darwinopterans around the world demonstrates the success of the group, originally only known from several species discovered in theTiaojishan Formation ofChina.[1]
As a darwinopteran,Ceoptera was a close relative of thepterodactyloid radiation that included most known pterosaurs, with intermediate anatomy between pterodactyloids and earlier "rhamphorhynchoid" pterosaurs. They are united with pterodactyloids in the groupMonofenestrata, most notably characterized by the fusion of theirnasal andantorbitalfenestra into a single large hole in the skull.[1] Due to the consistent anatomy seen in these pterosaurs, the authors supported the existence of Darwinoptera as anatural grouping, an offshoot whose intermediate nature was inherited from a common ancestor with pterodactyloids. Other studies, however, find that anatomical form to merely be a transitional stage in pterosaur evolution, and consider thesetaxa to besuccessively distant relatives ofPterodactyloidea.[1][8][9] As a rare Middle Jurassic pterosaur,Ceoptera existed at a key point in the diversification of darwinopterans and other pterosaurs. Combined with other lines of evidence emerging in the 2010s and 2020s, its discovery is considered indicative that many groups of pterosaurs emerged in theEarly Jurassic and had achieved a high level of ecological diversity by the Middle Jurassic, despite the paucity of fossils.[1]
The results of the 2024 analysis are shown below:[1]
Known remains ofCeoptera are found in theKilmaluag Formation, part of theGreat Estuarine Group and dating to theBathonian age of theJurassic 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 closedlagoon ecosystem near the ocean fed bymeteoric 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 inCeoptera. 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 exposedsupralittoral ecosystem which was significantly more barren than the vertebrate beds.[1][5][10]
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 theForest Marble Formation, a formation of similar age found inEngland. Plant fossils, contrastingly, are extremely rare within the Kilmaluag Formation, mostly restricted togymnosperm pollen andpteridophyte spores. Invertebrates are best represented by extremely abundant freshwaterostracods such asDarwinula andTheriosynoecum. Other invertebrates includeconchostracansAnthronesteria andPseudograpta, the gastropodViviparus, and thebivalveUnio.[5] Burrows indicate the presence of shrimps or crabs.[5][11] Insects fossils are not common, but include beetles. Fish include thehybodontsAcrodus andHybodus,pycnodonts, thesemionotiformLepidotes,amiiforms, and asarcopterygian that may be a type ofcoelacanth. Amphibians include thekarauridMarmorerpeton wakei, a very primitive form ofsalamander, as well as thealbanerpetontidAnoualerpeton; frogs are seemingly absent.[5][12]
Many reptiles are found in the formation, with the earlylepidosauromorphMarmoretta being the most common. Lizards includeBellairsia gracilis,Balnealacerta, andParviraptor are also found in the formation.[5][13]Rhynchocephalians appear to be absent. Aquatic reptiles include thechoristodereCteniogenys, and turtle remains are common, includingEileanchelys, one of the earliest aquatic turtles.[5][14]Crocodylomorphs are represented byatoposaurids andgoniopholids.[5][15] Dinosaurs are primarily known from tracks, indicating the presence ofmegalosauridtheropods and largeeusauropods.[10] Aneornithischiann dinosaur, possibly the oldest knownornithopod, is represented by a partial skeleton.[16] Mammals include thetritylodontidStereognathus ooliticus,[17] thedocodontsBorealestes serendipitus,Borealestes cuillinensis, andKrusatodon kirtlingtonensis,[18][19] themorganucodontWareolestes rex,[20] thecladotherianPalaeoxonodon ooliticus,[21] andPhascolotherium.Multituberculates andharamiyidans notably appear absent.[5]
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