Cimoliopterus is a genus of pterosaur that lived during the Late Cretaceous in what is now England and the United States. The first known specimen, consisting of the front part of a snout including part of a crest, was discovered in the Grey Chalk Subgroup of Kent, England, and described as the new species Pterodactylus cuvieri in 1851. The specific name cuvieri honoured the palaeontologist George Cuvier, and the genus Pterodactylus was then used for many pterosaurs of species that are no longer thought to be closely related. It was among the first pterosaurs to be depicted as sculptures, in Crystal Palace Park in the 1850s. The species was subsequently assigned to various other genera, including Ornithocheirus and Anhanguera. In 2013, the species was moved to a new genus, as Cimoliopterus cuvieri; the generic name Cimoliopterus is derived from the Greek words for "chalk" and "wing". Other specimens and species have also been assigned to or synonymised with the species with various levels of certainty. In 2015, a snout discovered in the Britton Formation of Texas, US, was named as a new species in the genus, C. dunni; the specific name honours its collector, Brent Dunn.

C. cuvieri is estimated to have had a wingspan of 3.5 metres (11 ft), and C. dunni is thought to have been similar to C. cuvieri in size. Cimoliopterus can be distinguished from related pterosaurs in features such as having a premaxillary crest that begins hindward on the snout, in having a ridge on the palate that extends forwards until the third pair of tooth sockets, and in the spacing and proportions of the tooth sockets. Unlike similar pterosaurs, the tip of the snout is only subtly expanded to the sides. C. cuvieri and C. dunni differ from each other in various details in the configuration of these features; for example, the crest of C. cuvieri begins by the seventh tooth socket, whereas that of C. dunni begins at the fourth. More completely known related genera were fairly large pterosaurs, with proportionally large skulls, long jaws and tooth-rows, often with large, rounded crests at the front of the jaws. The teeth at the front of the jaws were large and recurved; further back, the teeth were smaller, slightly recurved, and well-spaced. As pterosaurs, Cimoliopterus would have been covered in pycnofibres (hair-like filaments), and had extensive wing-membranes, which were distended by long wing-fingers.

While long considered an ornithocheiran, the affinities of C. cuvieri were unclear due to the fragmentary nature of it and other English pterosaurs, until more complete relatives were reported from Brazil in the 1980s. Cimoliopterus was moved to the family Cimoliopteridae within the clade Targaryendraconia in 2019, with its closest relative being Camposipterus. That C. cuvieri from England and C. dunni from North America were so similar despite living on opposite sides of the North Atlantic Ocean indicates they became less isolated from each other than other animal groups because they could fly. This kind of pterosaur was probably adapted for long-distance oceanic soaring, which is also supported by their fossils mainly being found in marine settings. While they may have been proficient in water, their terrestrial abilities were limited due to their having short hindlimbs but long forelimbs. They possibly fed while flying by dipping their long jaws into water and catching fish with their interlocking teeth. While some have suggested the premaxillary crests were used to stabilise the jaws while submerged in water during feeding, they may have been used as display structures.

The taxonomic history of Cimoliopterus and related pterosaurs from the Cretaceous of England has been described as confusing by modern pterosaur researchers, since many of them were described from very fragmentary remains, and named using convoluted nomenclatural schemes of the Victorian era. Prior to these discoveries, many of the hollow, thin-walled pterosaur bones found in England were thought to have belonged to birds. In 1851, the British naturalist James Scott Bowerbank described a large pterosaur snout he had obtained, which was found in the Lower Culand Pit in what is now called the Grey Chalk Subgroup at Burham, Kent, in South East England. Pterosaur fossils had been discovered earlier in the same pit, including the front part of some jaws Bowerbank had used as the basis for the species Pterodactylus giganteus in 1846, as well as other bones. Based on the new snout, Bowerbank named the species Pterodactylus cuvieri; at this time, the genus Pterodactylus (originally named in 1815 based on a Bavarian specimen) was used for many pterosaur species now thought to be only distantly related to each other. The specific name honours the French palaeontologist Georges Cuvier, who had recognised that pterosaurs were flying reptiles. In full, the name can be translated as "Cuvier's wing finger".

The snout which Bowerbank made the holotype specimen (on which the scientific name is based) of P. cuvieri consists of the front of the upper jaw, including part of a premaxillary crest (a crest on the premaxilla, the frontmost bone of the upper jaw), and is catalogued today as NHMUK PV 39409 at the Natural History Museum in London. It was originally reported to preserve a single tooth in the first right tooth socket (at the front of the snout), but this had disappeared when the holotype was examined in the 2000s. Two complete teeth were also originally reported to be preserved in the same block of chalk as the snout. Bowerbank also believed some large bones in three other collections may either have belonged to the same species, to P. giganteus, or to a third possible species. The British biologist Richard Owen assigned one long bone to P. cuvieri in 1851 (today catalogued as NHMUK PV 41637) based on its size and the character of its surface, and identified it as a possible phalanx bone of the elongated wing-finger.

In the 1850s the British artist Benjamin Waterhouse Hawkins created full-sized sculptures of prehistoric animals for Crystal Palace Park in London, under the supervision of Owen. Among them were two species of pterosaur, including two P. cuvieri sculptures made of iron-framed concrete and two smaller statues of Pterodactylus bucklandi. While Owen only identified one of the large sculptures as P. cuvieri in 1854, they are similar enough that they can be assumed to depict the same species. Hawkins' sculptures were the first to depict pterosaurs, and the oldest life reconstructions of giant members of the group. Incidentally, he thought these animals to be the original dragons, such as in the legend of Saint George. The larger P. cuvieri statues are today in disrepair due to their delicate nature and vandalism, and the smaller ones have been lost. The British palaeontologist Mark Witton stated in 2019 that the anatomy of the sculptures was probably based on the (by then) more completely known P. antiquus. They were depicted with scales (though pterosaurs are now known to have had a hair-like covering, a feature already realised by some scientists at the time) and bird-like proportions such as small heads and large torsos, as was customary at the time. One sculpture is correctly shown in a quadrupedal pose, and with one foot flat on the ground. While this pterosaur was one of the first known preserved with a crest at the tip of the jaw, this feature is not included in the sculptures, as it seems they were assumed to have been more similar to those of P. antiquus. Witton and the British biologist Ellinor Michel said in 2023 that while it was the largest known pterosaur at the time, its historical significance was overshadowed by the 1870 discovery of the larger Pteranodon, a genus that was widely featured in text and artwork, while the Crystal Palace sculptures remained the only major publicity of P. antiquus.

In 1869, the British palaeontologist Harry Govier Seeley placed P. cuvieri in the new genus Ptenodactylus along with other English pterosaurs known mainly from upper jaws, in an index of specimens in the Woodwardian Museum. He noted these names were provisional, only intended for the convenience of students using the museum, and not necessarily as names for these species. In 1870, Seeley placed the species in the genus Ornithocheirus, which he had originally used for other species in his 1869 index, and figured a dentary bone (front bone of the mandible) he listed belonged to O. cuvieri. In 1874, Owen assigned the species to the genus Coloborhynchus. The British palaeontologist Reginald Walter Hooley used the name O. cuvieri in his 1914 revision of Ornithocheirus, using Seeley's terminology.

In 1922, the Austrian naturalist Gustav von Arthaber lamented that the scientific literature had accepted the many Ornithocheirus names that had only been mentioned in Seeley's catalogue for students. In his opinion names were of no use without an illustration of the specimens they were based on, or better still, a complete reconstruction of the relevant skeleton. For this reason, he provided a drawing of the skull of O. cuvieri (among other species), one of the few species for which the known jaw material proved its validity. In 1924, von Arthaber's interpretations were criticised by the Hungarian palaeontologist Franz Nopcsa von Felső-Szilvás, who found some of the skull reconstructions "worthless".

O. cuvieri and many other English pterosaurs were kept in the genus Ornithocheirus for most of the 20th century. In 1987, the German palaeontologist Peter Wellnhofer described the new crested pterosaur Tropeognathus from the Santana Formation of Brazil and noted the similarities between it and other newly described Brazilian taxa such as Anhanguera to English taxa that were based on fragmentary snouts, such as the various species assigned to Ornithocheirus. He concluded that while the appearance of the English taxa had long been a puzzle (leading for example to von Arthaber's unusual reconstructions), the discovery of the related and much better preserved Brazilian species made this clearer, showing that the English species too had premaxillary crests at the end of large, long skulls. When Anhanguera was described in 1985, it was thought to be the only pterosaur with such a crest known until that point (then referred to as a sagittal crest). In 1991, Wellnhofer stated that the genus Ornithocheirus had become a "wastebin" of species from different countries, assigned to it on the basis of insufficient characters, and needed clearer definition, and perhaps included several distinct genera.

The British palaeontologist S. Christopher Bennett stated in 1993 that the holotype specimen of O. cuvieri was the right first wing-phalanx bone mentioned by Owen in 1851, and cited him for the name without further explanation. In 1995, the Russian palaeontologist Natalia N. Bakhurina and the British palaeontologist David M. Unwin assigned a partial mandibular symphysis (the part connecting the two halves of the lower jaw) from Russia to cf. Anhanguera cuvieri (from Latin "confer", possibly belonging to this or a related animal), thereby using a new combination. Unwin and colleagues assigned pterosaur skeletal elements from the Toolebuc Formation of Australia to Anhanguera ?cuvieri in 2000. In 2001, Unwin also used the combination A. cuvieri, and cited Bowerbank for the name, with the snout as holotype. He assigned 23 jaw fragment from the Cambridge Greensand Formation to A. cuvieri and considered it the most common pterosaur of that formation. Unwin concluded that the species O. brachyrhinus, O. colorhinus, O. dentatus, O. denticulatus, O. enchorhynchus, O. scaphorhynchus and O. xyphorhynchus were junior synonyms of A. cuvieri. He also considered a species originally named Pterodactylus fittoni by Owen in 1859 as a member of Anhanguera. In 2011, the Brazilian palaeontologist Alexander W. Kellner and colleagues made the Australian material that had been assigned to A. ?cuvieri the basis of a new genus, Aussiedraco, and stated that they saw no ground for placing O. cuvieri in Anhanguera.

In 2013, the Brazilian palaeontologist Taissa Rodrigues and Kellner reviewed the species that had so far been placed in the genus Ornithocheirus (which they restricted to its type species, O. simus), as well as other English Cretaceous pterosaurs. They concluded that A. cuvieri differed enough from its relatives to be placed in a new, monotypic genus; Cimoliopterus. This generic name combines the Greek words Kimolia (Κιμωλία), which means "chalk", and pteron, (πτερόν) meaning "wing". In full, the name can be translated as "Cuvier's chalk wing". Rodrigues and Kellner also found that while the species P. fittoni, O. brachyrhinus, and O. enchorhynchus had various features in common with C. cuvieri, and could therefore not be excluded from that genus, they were too fragmentary to be assigned to it definitively and were considered nomina dubia (dubious names). They considered other species that were assigned to A. cuvieri by Unwin in 2001 dubious or belonging to other taxa. They also considered the Russian specimen assigned to cf. A. cuvieri in 1995 unrelated. In 2019, the Brazilian palaeontologist Rodrigo V. Pêgas and colleagues suggested that the type specimen of Lonchodectes (a dubious genus originally known as Pterodactylus compressirostris) represented by a partial mandibular symphysis from the Chalk Group, could represent the same species as C. cuvieri. They cautioned this is impossible to confirm until associated skull and mandible material is found.

In 2013, the American amateur fossil collector Brent Dunn discovered a pterosaur snout fragment in the Britton Formation near Lewisville Lake, northwest of Dallas, Texas, US. He donated the specimen to the Shuler Museum of Paleontology of Southern Methodist University, where it is catalogued as SMU 76892. In 2015, the American palaeontologist Timothy S. Myers described the specimen and made it the holotype of the new species Cimoliopterus dunni; the specific name honours Dunn, who died in 2013. The holotype specimen of C. dunni consists of the front part of a snout, including part of a premaxillary crest. The fossil was initially covered by a thin layer of red clay, which was prepared away. The three-dimensionally preserved fossil does not appear to have suffered the extreme crushing often seen in pterosaur fossils, though some of the hind part was distorted by compaction. C. dunni was only the third toothed pterosaur known from the Cretaceous of North America.

Because the fossils are incomplete, the size of Cimoliopterus is difficult to estimate. Extrapolating from the remains of more complete pterosaur species, as well as various bones possibly belonging to C. cuvieri, Bowerbank estimated a wingspan of about 5.1 metres (16.6 ft) in 1851. This was larger than the estimates for the earlier named P. giganteus (now in the genus Lonchodraco), which he had considered "gigantic" for a pterosaur. Later the same year, Owen called C. cuvieri "truly gigantic", compared to P. giganteus, which he felt was therefore inaccurately named. In 2001, comparing the C. cuvieri holotype specimen with the more complete Anhanguera, Unwin estimated a wingspan of about 3.5 metres (11 ft). He estimated an assigned specimen, CAMSM B54.431, to have had a wingspan of up to 5 metres (16 ft). In 2013, this specimen—originally a syntype snout tip of Ornithocheirus colorhinus—was tentatively assigned instead to Camposipterus by Rodrigues and Kellner. Witton and Michel gave a 4 metres (13 ft) wingspan for C. cuvieri in 2023, but cautioned it was "rough" due to the poor fossils. In 2015, Myers stated the holotypes of C. cuvieri and C. dunni belonged to individuals of a similar size. C. dunni would have been mid-sized for a pterosaur, with a wingspan of about 1.8 metres (6 ft), according to a press release accompanying its description. In 2019, Pêgas and colleagues refrained from estimating wingspans for such species represented by too fragmentary material.

More completely known related genera were fairly large pterosaurs, with proportionally large skulls, long jaws and tooth-rows, and often with large, rounded crests at the front of the jaws. The teeth at the front of the jaws were large and recurved, and further back the teeth were smaller, slightly recurved, and well-spaced. Much of the skeleton would have been pneumatised (filled with air sacs that lightened it). The necks were proportionally long, and the torsos relatively small. The forelimbs were proportionally enormous compared to the legs, with very long wing-fingers. As a pterosaur, Cimoliopterus would have been covered in pycnofibres (hair-like filaments), and had extensive wing-membranes, which were distended by the wing-fingers.

Rodrigues and Kellner provided a single diagnosis (a list of features distinguishing a taxon from its relatives) for the genus Cimoliopterus and species C. cuvieri in 2013, which Myers amended in 2015 when including C. dunni. The holotype snouts of the two Cimoliopterus species share features that distinguish them from other pterodactyloid (or short-tailed) pterosaurs such as a premaxillary crest that begins hindward on the snout and that the palatal ridge (which ran along the middle of the palate) extended forwards until the third tooth socket pair. In both species, the second and third tooth sockets are similar in size and larger than the fourth. The spacing between the sockets is irregular, with those towards the front being more closely spaced, and those towards the back more widely separated. There are three tooth sockets per 3 cm (1 in) of jaw margin towards the front of the jaw in C. dunni, while in C. cuvieri there are almost three sockets per 3 cm (1 in). However, towards the back of the jaw, there are two sockets every 3 cm (1 in) in both species. The palate is curved upwards. The snout tips of C. cuvieri and C. dunni are only expanded subtly from side to side, unlike the "spoon-like" expansions seen in many other toothed pteranodontoids, such as Anhanguera, Coloborhynchus, and Ornithocheirus. The subtle sideways expansion on the snout tip of Cimoliopterus results from the third pair of sockets being larger than the fourth pair, similar to what can be seen on the lower jaw of Aetodactylus. The subtle expansion is so weakly developed that it has been thought absent at times.