Pteranodon

First fossils Pteranodon was the first pterosaur found outside of Europe. Its fossils first were found by Othniel Charles Marsh in either 1870 in the Late Cretaceous Smoky Hill Chalk deposits of western Kansas. These chalk beds were deposited at the bottom of what was once the Western Interior Seaway, a large shallow sea over what now is the midsection of the North American continent. These first specimens, YPM 1160 and YPM 1161, consisted of partial wing bones, as well as a tooth from the prehistoric fish Xiphactinus, which Marsh mistakenly believed to belong to this new pterosaur (all known pterosaurs up to that point had teeth). In 1871, Marsh named the find Pterodactylus oweni, assigning it to the well-known (but much smaller) European genus Pterodactylus. Marsh also collected more wing bones of the large pterosaur in 1871. Realizing that the name he had chosen had already been used for Harry Seeley's European pterosaur species Pterodactylus oweni in 1864, Marsh renamed his giant North American pterosaur Pterodactylus occidentalis, meaning "Western wing finger," in his 1872 description of the new specimen. He named two additional species, based on size differences: Pterodactylus ingens (the largest specimen so far), and Pterodactylus velox (the smallest). Re-evaluation by later scientists has supported Marsh's case, refuting Cope's assertion that P. umbrosus represented a larger, distinct species. A second, smaller skull soon was discovered as well. These skulls showed that the North American pterosaurs were different from any European species, in that they lacked teeth and had bony crests on their skulls. Marsh recognized this major difference, describing the specimens as "distinguished from all previously known genera of the order Pterosauria by the entire absence of teeth." Marsh recognized that this characteristic warranted a new genus, and he coined the name Pteranodon ("wing without tooth") Marsh also named several additional species: Pteranodon comptus and Pteranodon nanus were named for fragmentary skeletons of small individuals, while Pteranodon gracilis was based on a wing bone that he mistook for a pelvic bone. He soon realized his mistake, and re-classified that specimen again into a separate genus, which he named Nyctosaurus. P. nanus was also later recognized as a Nyctosaurus specimen. Revising species Williston was also the first scientist to critically evaluate all of the Pteranodon species classified by Cope and Marsh. He agreed with most of Marsh's classification, with a few exceptions. First, he did not believe that P. ingens and P. umbrosus could be considered synonyms, which even Cope had come to believe. He considered both P. velox and P. longiceps to be dubious; the first was based on non-diagnostic fragments, and the second, though known from a complete skull, probably belonged to one of the other, previously-named species. In 1903, Williston revisited the question of Pteranodon classification, and revised his earlier conclusion that there were seven species down to just three. He considered both P. comptus and P. nanus to be specimens of Nyctosaurus, and divided the others into small (P. velox), medium (P. occidentalis), and large species (P. ingens), based primarily on the shape of their upper arm bones. He thought P. longiceps, the only one known from a skull, could be a synonym of either P. velox or P. occidentalis, based on its size. though this was later changed to simply Pteranodon due to the rules of priority. P. sternbergi and P. walkeri, the upright-crested species, were given the subgenus Sternbergia, Finally, Miller named the subgenus Occidentalia for P. eatoni, the skull formerly associated with P. occidentalis. Miller further expanded the concept of Pteranodon to include Nyctosaurus as a fourth subgenus. Miller considered these to be an evolutionary progression, with the primitive Nyctosaurus, at the time thought to be crestless, giving rise to small-crested Occidentalia, which in turn gave rise to long-crested Pteranodon, finally leading to tall-crested Geosternbergia. Recognizing variation In the late 1980s and early 1990s, S. Christopher Bennett published several major papers reviewing the anatomy, taxonomy and life history of Pteranodon. In the 1992 paper, he referred only to two species, P. longiceps and P. sternbergi. Two years later, he published a paper fully revising its taxonomy, wherein he concluded that only P. longiceps and P. sternbergi were valid species. P. marshi and P. walkeri were regarded as junior synonyms of P. longiceps, and P. eatoni as a junior synonym of P. stenbergi. The remainder were either rendered nomina dubia or placed in Nyctosaurus. ==Description==

Body size and sexual dimorphism Adult male Pteranodon were among the largest pterosaurs, and were the largest flying animals known until the late 20th century, when the giant azhdarchid pterosaurs were discovered. The wingspan of an average adult male Pteranodon was . Adult females were much smaller, averaging in wingspan. A large specimen of Pteranodon longiceps, USNM 50130, is estimated to have a wingspan of , body length of and body mass of . Even larger specimens had wingspans of . Size aside, females were distinguished by their short, rounded head crests and wide pelvic canals, whereas males had narrow hips and very large head crests, likely serving a display function. The most distinctive characteristic of Pteranodon is its cranial crest. These crests consisted of skull bones (frontals) projecting upward and backward from the skull. The size and shape of these crests varied due to a number of factors, including age, sex, and species. Male Pteranodon sternbergi, the older species of the two described to date, had a more vertical crest with a broad forward projection, while their descendants, Pteranodon longiceps, evolved a narrower, more backward-projecting crest. Like many pterosaurs and birds, it possessed a notarium, a fused mass comprising the first six dorsal vertebrae. Similarly, the first few ribs were fused. The humeri were extremely robust, with large, curved deltopectoral crests. The radius and ulna were similarly robust. The first three metacarpals were very slender, and their respective digits sported short, curved unguals (claws). Pteranodon's hind feet had four metatarsals, which were tipped with less curved claws. ==Paleobiology==

Flight The wing shape of Pteranodon suggests that it would have flown rather like a modern-day albatross. This is based on the fact that Pteranodon had a high aspect ratio (wingspan to chord length) similar to that of the albatross — 9:1 for Pteranodon, compared to 8:1 for an albatross. Albatrosses spend long stretches of time at sea fishing, and use a flight pattern called "dynamic soaring" which exploits the vertical gradient of wind speed near the ocean surface to travel long distances without flapping, and without the aid of thermals (which do not occur over the open ocean the same way they do over land). While most of a Pteranodon flight would have depended on soaring, like long-winged seabirds, it probably required an occasional active, rapid burst of flapping, and studies of Pteranodon wing loading (the strength of the wings vs. the weight of the body) indicate that they were capable of substantial flapping flight, contrary to some earlier suggestions that they were so big they could only glide. However, a more recent study suggests that it relied on thermal soaring, unlike modern seabirds but much like modern continental flyers and the extinct Pelagornis. Like other pterosaurs, Pteranodon probably took off from a standing, quadrupedal position. Using their long forelimbs for leverage, they would have vaulted themselves into the air in a rapid leap. Almost all of the energy would have been generated by the forelimbs. The upstroke of the wings would have occurred when the animal cleared the ground followed by a rapid down-stroke to generate additional lift and complete the launch into the air. which has been speculated for various other such as the distantly related Anhanguera. Locomotion Historically, terrestrial locomotion in Pteranodon, as in pterosaurs overall, has been the subject of debate, chiefly the matter of whether or not they were bipedal or quadrupedal. The earliest model of Pteranodon locomotion, put forward by Cherrie D. Bramwell and G. R. Whitfield, suggested that they were utterly incapable of walking or standing. Instead, they suggested that it moved on land by pushing itself around, and that it took off by perching on cliffsides and allowing the wind to take it. Subsequent works largely revolved around more conventional methods of locomotion, such as bipedalism and various kinds of quadrupedalism. In 2004, Sankar Chatterjee and R. J. Templin proposed a dual system, wherein pterosaurs walked quadrupedally most of the time, but opted for a bipedal takeoff. Diet The diet of Pteranodon is known to have included fish; Therefore, display was probably the main function of the crest, and any other functions were secondary. Bennett (1992) agreed with Eaton's own assessment that the crest was too large and variable to have been a muscle attachment site. One researcher, Ross S. Stein, even suggested that the crest may have supported a membrane of skin connecting the backward-pointing crest to the neck and back, increasing its surface area and effectiveness as a rudder. The rudder hypothesis, again, does not take into account females nor P. sternbergi, which had an upward-pointing, not backward-pointing crest. Bennett also found that, even in its capacity as a rudder, the crest would not provide nearly so much directional force as simply maneuvering the wings. The suggestion that the crest was an air brake, and that the animals would turn their heads to the side in order to slow down, suffers from a similar problem. Additionally, the rudder and air brake hypotheses do not explain why such large variation exists in crest size even among adults. The gender of the different size classes was determined, not from the skulls, but from the pelvic bones. Contrary to what may be expected, the smaller size class had disproportionately large and wide-set pelvic bones. Bennett interpreted this as indicating a more spacious birth canal, through which eggs would pass. He concluded that the small size class with small, triangular crests represent females, and the larger, large-crested specimens represent males. The fact that females appear to have outnumbered males two to one suggests that, as with modern animals with size-related sexual dimorphism, such as sea lions and other pinnipeds, Pteranodon might have been polygynous, with a few males competing for association with groups consisting of large numbers of females. Similar to modern pinnipeds, Pteranodon may have competed to establish territory on rocky, offshore rookeries, with the largest, and largest-crested, males gaining the most territory and having more success mating with females. The crests of male Pteranodon would not have been used in competition, but rather as "visual dominance-rank symbols", with display rituals taking the place of physical competition with other males. If this hypothesis is correct, it also is likely that male Pteranodon played little to no part in rearing the young; such a behavior is not found in the males of modern polygynous animals who father many offspring at the same time. In 2017, Bennett described the smallest known specimen of Pteranodon: FHSM 17956, an incomplete right wing from the Smoky Hill Chalk. It is from a juvenile with an estimated wingspan of . Other than in size, it was not found to differ from larger specimens. Bennett interpreted its presence in the Smoky Hill Chalk—an open ocean setting lacking small terrestrial vertebrates—as indication that juvenile Pteranodon were precocial and already capable of flying long distances. Because juveniles are otherwise unknown in the Smoky Hill Chalk, Bennett inferred that they occupied different environments and ecological niches than adults. A 2023 study by Yang et al. assessed wing ontogeny and performance in Pteranodon compared to Sinopterus, Pterodactylus, Rhamphorhynchus, and anurognathids. They found that, unlike the smaller pterosaurs, Pteranodon's limbs showed positive allometry, meaning they grew at a faster rate than the rest of the skeleton; this suggests Pteranodon became better fliers as they grew. Thus, in contrast with Bennett 2017, Yang et al. concluded Pteranodon was more altricial than smaller pterosaurs, with early juveniles requiring parental care; though they may still have had wings capable of flight, they likely only flew occasionally so as to maintain a low tissue maturity and high growth rate. ==Paleoecology==

during the mid-Cretaceous period, illustrating the Western Interior Seaway (middle to upper left) and other nearby seaways Specimens assigned to Pteranodon have been found in both the Smoky Hill Chalk deposits of the Niobrara Formation, and the slightly younger Sharon Springs deposits of the Pierre Shale Formation. When Pteranodon was alive, this area was covered by a large inland sea, known as the Western Interior Seaway. Famous for fossils collected since 1870, these formations extend from as far south as Kansas in the United States to Manitoba in Canada. However, Pteranodon specimens (or any pterosaur specimens) have only been found in the southern half of the formation, in Kansas, Wyoming, and South Dakota. Despite the fact that numerous fossils have been found in the contemporary parts of the formation in Canada, no pterosaur specimens have ever been found there. This strongly suggests that the natural geographic range of Pteranodon covered only the southern part of the Niobrara, and that its habitat did not extend farther north than South Dakota. Fossils from terrestrial dinosaurs also have been found in the Niobrara Chalk, suggesting that animals who died on shore must have been washed out to sea (one specimen of a hadrosaur appears to have been scavenged by a shark). It is likely that, as in other polygynous animals (in which males compete for association with harems of females), Pteranodon lived primarily on offshore rookeries, where they could nest away from land-based predators and feed far from shore; most Pteranodon fossils are found in locations which at the time, were hundreds of kilometres from the coastline. ==Classification==

Timespan and evolution Pteranodon fossils are known primarily from the Niobrara Formation of the central United States. Broadly defined, Pteranodon existed for more than four million years, during the Santonian stage of the Cretaceous period. The genus is present in most layers of the Niobrara Formation except for the upper two; in 2003, Kenneth Carpenter surveyed the distribution and dating of fossils in this formation, demonstrating that Pteranodon sternbergi existed there from 88 to 85 million years ago, while P. longiceps existed between 86 and 84.5 million years ago. A possible third species, which Kellner named Geosternbergia maiseyi in 2010, is known from the Sharon Springs member of the Pierre Shale Formation in Kansas, Wyoming, and South Dakota, dating to between 81.5 and 80.5 million years ago. Fossils of P. longiceps have been found in layers dating to 80-78.25 million years ago. In the early 1990s, Bennett noted that the two major morphs of pteranodont present in the Niobrara Formation were precisely separated in time with little, if any, overlap. Due to this, and to their gross overall similarity, he suggested that they probably represent chronospecies within a single evolutionary lineage lasting about 4 million years. In other words, only one species of Pteranodon would have been present at any one time, and P. sternbergi (or Geosternbergia) in all likelihood was the direct ancestor species of P. longiceps. It was collected by George F. Sternberg in 1952 and described by John Christian Harksen in 1966, from the lower portion of the Niobrara Formation. It was older than P. longiceps and is considered by Bennett to be the direct ancestor of the later species. }} Alternative classifications Due to the subtle variations between specimens of pteranodontid from the Niobrara Formation, most researchers have assigned all of them to the single genus Pteranodon, in at least two species (P. longiceps and P. sternbergi) distinguished mainly by the shape of the crest. However, the classification of these two forms has varied from researcher to researcher. In 1972, Halsey Wilkinson Miller published a paper arguing that the various forms of Pteranodon were different enough to be placed in distinct subgenera. He named these Pteranodon (Occidentalia) occidentalis (for the now-disused species P. occidentalis) and Pteranodon (Sternbergia) sternbergi. However, the name Sternbergia was preoccupied, and in 1978 Miller re-named the species Pteranodon (Geosternbergia) sternbergi, and named a third subgenus/species combination for P. longiceps, as Pteranodon (Longicepia) longiceps. Most prominent pterosaur researchers of the late 20th century however, including S. Christopher Bennett and Peter Wellnhofer, did not adopt these subgeneric names, and continued to place all pteranodont species into the single genus Pteranodon. In 2010, pterosaur researcher Alexander Kellner revisited H.W. Miller's classification. Kellner followed Miller's opinion that the differences between the Pteranodon species were great enough to place them into different genera. He placed P. sternbergi into the genus named by Miller, Geosternbergia, along with the Pierre Shale skull specimen which Bennett had previously considered to be a large male P. longiceps. Kellner argued that this specimen's crest, though incompletely preserved, was most similar to Geosternbergia. Because the specimen was millions of years younger than any known Geosternbergia, he assigned it to the new species Geosternbergia maiseyi. Numerous other pteranodont specimens are known from the same formation and time period, and Kellner suggested they may belong to the same species as G. maiseyi, but because they lack skulls, he could not confidently identify them. Disused species A number of additional species of Pteranodon have been named since the 1870s, although most now are considered to be junior synonyms of two or three valid species. The best-supported is the type species, P. longiceps, based on the well-preserved specimen including the first-known skull found by S. W. Williston. This individual had a wingspan of . Other valid species include the possibly larger P. sternbergi, with a wingspan originally estimated at . P. oweni (P. occidentalis), P. velox, P. umbrosus, P. harpyia, and P. comptus are considered to be nomina dubia by Bennett (1994) and others who question their validity. All probably are synonymous with the more well-known species. Because the key distinguishing characteristic Marsh noted for Pteranodon was its lack of teeth, any toothless pterosaur jaw fragment, wherever it was found in the world, tended to be attributed to Pteranodon during the late nineteenth and early twentieth centuries. This resulted in a plethora of species and a great deal of confusion. The name became a wastebasket taxon, rather like the dinosaur Megalosaurus, to label any pterosaur remains that could not be distinguished other than by the absence of teeth. Species (often dubious ones now known to be based on sexual variation or juvenile characters) have been reclassified a number of times, and several subgenera have in the 1970s been erected by Halsey Wilkinson Miller to hold them in various combinations, further confusing the taxonomy (subgenera include Longicepia, Occidentalia, and Geosternbergia). Notable authors who have discussed the various aspects of Pteranodon include Bennett, Padian, Unwin, Kellner, and Wellnhofer. Two species, P. oregonensis and P. orientalis, are not pteranodontids and have been renamed Bennettazhia oregonensis and Bogolubovia orientalis respectively. List of species and synonyms Status of names listed below follow a survey by Bennett, 1994 unless otherwise noted. ==See also==