Genus of pteranodontid pterosaur from the Late Cretaceous
Pteranodon (; from 'wing' and 'toothless') is a genus of pterosaur that included some of the largest known flying reptiles, with "P. longiceps" having a wingspan of over . They lived during the late Cretaceous geological period of North America in present-day Kansas, Nebraska, Wyoming, South Dakota and Alabama. More fossil specimens of "Pteranodon" have been found than any other pterosaur, with about 1,200 specimens known to science, many of them well preserved with nearly complete skulls and articulated skeletons. It was an important part of the animal community in the Western Interior Seaway.
When the first fossils of "Pteranodon" were found, they were assigned to toothed pterosaur genera, "Ornithocheirus" and "Pterodactylus". In 1876, Othniel Charles Marsh recognised it as a genus of its own, making particular note of its complete lack of teeth, which at the time was unique among pterosaurs. Over the decades, multiple species would be assigned to "Pteranodon", though today, only two are recognised: "P. longiceps", the type species, and "P. sternbergi". A third species, "P. maiseyi", may also exist. Some have suggested that the latter two as genus of their own, "Geosternbergia", though this is the subject of some debate. Another genus split from "Pteranodon", "Dawndraco", may be synonymous with "Geosternbergia" if that genus is valid, or with "Pteranodon" if it is not.
"Pteranodon" is part of the family Pteranodontidae, part of the clade Pteranodontia, which also includes nyctosaurids. Pteranodontians form a larger clade, Pteranodontoidea, alongside ornithocheiromorphs, and that clade falls under the suborder Pterodactyloidea. While not dinosaurs, pterosaurs such as "Pteranodon" form a clade closely related to dinosaurs as both fall within the clade Avemetatarsalia.
Male and female "Pteranodon" differed in size and crest shape. Males attained wingspans of ; females were smaller, averaging . The crests of males were far larger than those of females. In "P. longiceps", they were long and backswept, whereas in "P. sternbergi", they were tall and upright. Females also had wider pelvises than males.
Discovery and history.
First fossils.
"Pteranodon" was the first pterosaur found outside of Europe. Its fossils first were found by Othniel Charles Marsh in 1871, 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).
Meanwhile, Marsh's rival Edward Drinker Cope had unearthed several specimens of the large North American pterosaur. Based on these specimens, Cope named two new species, Ornithochirus umbrosus and "Ornithochirus harpyia", in an attempt to assign them to the large European genus "Ornithocheirus", though he misspelled the name (forgetting the 'e'). Cope's paper naming his species was published in 1872, just five days after Marsh's paper. This resulted in a dispute, fought in the published literature, over whose names had priority in what obviously were the same species. Cope conceded in 1875 that Marsh's names did have priority over his, but maintained that "Pterodactylus umbrosus" was a distinct species (but not genus) from any that Marsh had named previously. Re-evaluation by later scientists has supported Marsh's case, refuting Cope's assertion that "P. umbrosus" represented a larger, distinct species.
A toothless pterosaur.
While the first "Pteranodon" wing bones were collected by Marsh and Cope in the early 1870s, the first "Pteranodon" skull was found on May 2, 1876, along the Smoky Hill River in Wallace County (now Logan County), Kansas, USA, by Samuel Wendell Williston, a fossil collector working for Marsh. 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") in 1876. Marsh reclassified all the previously named North American species from "Pterodactylus" to "Pteranodon". He considered the smaller skull to belong to "Pteranodon occidentalis", based on its size. Marsh classified the larger skull, YPM 1117, in the new species "Pteranodon longiceps", which he thought to be a medium-sized species in between the small "P. occidentalis" and the large "P. ingens". 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.
In 1892, Samuel Williston examined the question of "Pteranodon" classification. He noticed that, in 1871, Seeley had mentioned the existence of a partial set of toothless pterosaur jaws from the Cambridge Greensand of England, which he named "Ornithostoma". Because the primary characteristic Marsh had used to separate "Pteranodon" from other pterosaurs was its lack of teeth, Williston concluded that "Ornithostoma" must be considered the senior synonym of "Pteranodon". However, in 1901, Pleininger pointed out that "Ornithostoma" had never been scientifically described or even assigned a species name until Williston's work, and therefore had been a "nomen nudum" and could not beat out "Pteranodon" for naming priority. Williston accepted this conclusion and went back to calling the genus "Pteranodon". However, both Williston and Pleininger were incorrect, because unnoticed by both of them was the fact that, in 1891, Seeley himself had finally described and properly named "Ornithostoma", assigning it to the species "O. sedgwicki". In the 2010s, more research on the identity of "Ornithostoma" showed that it was probably not "Pteranodon" or even a close relative, but may in fact have been an azhdarchoid, a different type of toothless pterosaur.
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.
In 1910, Eaton became the first scientist to publish a more detailed description of the entire "Pteranodon" skeleton, as it was known at the time. He used his findings to revise the classification of the genus once again based on a better understanding of the differences in pteranodont anatomy. Eaton conducted experiments using clay models of bones to help determine the effects of crushing and flattening on the shapes of the arm bones Williston had used in his own classification. Eaton found that most of the differences in bone shapes could be easily explained by the pressures of fossilization, and concluded that no "Pteranodon" skeletons had any significant differences from each other besides their size. Therefore, Eaton was left to decide his classification scheme based on differences in the skulls alone, which he assigned to species just as Marsh did, by their size. In the end, Eaton recognized only three valid species: "P. occidentalis", "P. ingens", and "P. longiceps".
The discovery of specimens with upright crests, classified by Harksen in 1966 as the new species "Pteranodon sternbergi", complicated the situation even further. prompting another revision of the genus by Halsey W. Miller in 1972. Because it was impossible to determine crest shape for all of the species based on headless skeletons, Miller concluded that all "Pteranodon" species except the two based on skulls ("P. longiceps" and "P. sternbergi") must be considered "nomena dubia" and abandoned. The skull Eaton thought belonged to "P. ingens" was placed in the new species "Pteranodon marshi", and the skull Eaton assigned to "P. occidentalis" was re-named "Pteranodon eatoni". Miller also recognized another species based on a skull with a crest similar to that of "P. sternbergi"; Miller named this "Pteranodon walkeri". To help bring order to this tangle of names, Miller created three subgenera. "P. marshi" and "P. longiceps" were placed in the subgenus "Longicepia", 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", which was later changed to "Geosternbergia" because "Sternbergia" was preoccupied. 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". However, Miller made several mistakes in his study concerning which specimens Marsh had assigned to which species, and most scientists disregarded his work on the subject in their later research. In 1984, Robert Milton Schoch published another revision that essentially returned to Marsh's original classification scheme, most notably sinking "P. longiceps" as a synonym of "P. ingens".
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 1992, he published a paper discussing sexual dimorphism and its role in individual variation among "Pteranodon" fossils, a follow-up of a 1987 paper he authored on the same subject. 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 had narrow hips and very large head crests, likely serving a display function.
Methods used to estimate the mass of large male "Pteranodon" specimens (those with wingspans of about 7 meters) have been notoriously unreliable, producing a wide range of estimates. In a review of pterosaur size estimates published in 2010, Mark Witton and Michael Habib argued that the largest estimate of is much too high and an upper limit of is more realistic. Witton and Habib