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Pteranodon; Temporal range: ; Late Cretaceous, 86–84.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Mounted replica skeleton of an adult male P. longiceps at the American Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Family:	†Pteranodontidae
Subfamily:	†Pteranodontinae; Williston, 1892
Genus:	†Pteranodon; Marsh, 1876
Type species
	†Pteranodon longiceps; Marsh, 1876
Other species
	†P. sternbergi? ; Harksen, 1966;
Synonyms
	Genus synonymy Pteranodon (Longicepia) ; Miller, 1971 ; Pteranodon (Occidentalia) ; Miller, 1971 ; Geosternbergia? ; Miller, 1978 ; Dawndraco? ; Kellner, 2010 ; Species synonymy Pteranodon (Longicepia) longiceps ; (Marsh, 1876) ; Pteranodon marshi ; Miller, 1972 ; Pteranodon (Longicepia) marshi ; (Miller, 1972) ; Pteranodon (Pteranodon) marshi ; (Miller, 1972) ; Pteranodon walkeri ; Miller, 1972 ; Pteranodon (Geosternbergia) walkeri ; (Miller, 1972) ; Pteranodon (Sternbergia) walkeri ; (Miller, 1972) ; Geosternbergia sternbergi? ; (Harksen, 1966) ; Dawndraco kanzai? ; Kellner, 2010 ;

Pteranodon (/tɪˈrænədɒn/; from Greek πτερόν (pteron, meaning "wing"), ἀν (an, meaning "without"), and ὀδούς (odous or odont, meaning "tooth")) is a genus of pteranodontid pterodactyloid pterosaur discovered in at least two rock formations in North America, which date back to the Santonian and Campanian stages of the Late Cretaceous period, around 86 to 84.5 million years ago. Fossil remains of Pteranodon are currently the most common of all pterosaurs, with more than 1,100 different specimens identified, but even so, many of these lack completeness, and therefore not enough to give researchers very detailed anatomical information. Pteranodon lived throughout the United States, and some specimens were even found in other formations that extended as far north as Canada. During the Late Cretaceous, most of central United States and Canada was covered by a large inland sea called the Western Interior Seaway, this meant that Pteranodon likely lived near the coast, and led to the idea that its diet mainly consisted of fish.

Similar to other pterosaurs of its family, Pteranodon is mostly known for its elongated cranial crest, which projected upward and backward from the skull. In males, the crest is much more elongated than in females, a feature that can be distinguished easily between the two sexes, leading to the idea that Pteranodon was sexually dimorphic. Pteranodon is one of the few pterosaurs that had a uniquely built cranial crest, and paleontologists have concluded that it may have been used for heat exchange, allowing them to absorb or shed heat and regulate their body temperature, which also would account for the correlation between crest size and body size. Unfortunately, no evidence of extra blood vessels in the crests of Pteranodon has been found to prove this purpose.

When Pteranodon was unearthed in 1870, it was, back then, the largest known pterosaur, with wingspan estimates of about 6.25 meters (20.5 ft). Larger wingspan estimates have been done in the past however, and some have reached an impressive 7.25 meters (23.8 ft) based on specimens that were proportionally larger than any other known Pteranodon specimens. Throughout the history of Pteranodon, many species were also formerly assigned to it, e.g. Pteranodon sternbergi and Pteranodon gracilis, which are now thought to have been the genera Geosternbergia and Nyctosaurus. Some fossilized remains of Pteranodon have also been found to contain fish bones in the stomach area, and several fossilized fish bolus have been found between the jaws of another Pteranodon specimen.^[1]^[2]

History of discovery[edit]

Earliest finds[edit]

The first fossil remains of Pteranodon were uncovered in an 1870 expedition led by American paleontologist Othniel Charles Marsh, in the Smoky Hill Chalk deposits of the Niobrara Formation of western Kansas. Among several pterosaur bones that represented two individuals (specimens YPM 1160 and YPM 1161), a wing metacarpal (each one of the bones that form the intermediate part of the hand) was recovered. Marsh estimated a wing expanse, based on the wing metacarpal he had found, not less than 6.1 meters (20 ft), which is more than twice that of the largest European pterosaurs known at the time. This estimate also provided the ﬁrst indication that pterosaurs had wingspans in considerable excess of any modern ﬂying animals. In 1871, Marsh had found more wing remains of Pteranodon, and later created a new species called "Pterodactylus oweni", in honor of the British paleontologist Sir Richard Owen. Marsh also indicated the presence of teeth associated with the pterosaur remains, noting that they are "smooth and compressed",^[3]^[4] however, the supposed tooth that was found was actually from a fish called Xiphactinus.^[5] Marsh assumed that it belong to "P. oweni" given that virtually all pterosaurs known at that time had teeth.^[3]

Later, in 1872, Marsh had realized that the name he had chosen, "P. oweni", had already been used for a pterosaur species described by British paleontologist Harry Govier Seeley in 1864, Marsh renamed his discovery as Pterodactylus occidentalis (meaning "Western wing finger"). In the same year, Marsh recovered additional material of P. occidentalis, this included a complete wing that verified his 6.1-meter (20 ft) wingspan estimate. He also found additional specimens, YPM 1169 and YPM 1170, precisely wing elements from four individuals, which hinted a species with a wingspan measuring 6.7 meters (22 ft). Marsh assigned these new specimens to a new separate species called Pterodactylus ingens. He also, once again, assumed that this species bore teeth and described them as being relatively slender compared to P. occidentalis. Aside from P. ingens, Marsh also named another species: Pterodactylus velox, which is based on the distal end of a right wing metacarpal (situated further from the point of attachment) and the proximal end (situated closer from the point of attachment) of the first wing phalanx (digital bone) he had found. He also noted differences in the joints of the crushed limb bones of P. occidentalis and the two newly named species (P. ingens and P. velox), and used these differences, as well as their size, to separate them as different species.^[5]^[3]^[6]

In the same year, 1872, Marsh's rival, paleontologist Edward Drinker Cope, had also unearthed several specimens, including AMNH 1571 and AMNH 1572, which he believed that represented both large and small pterosaur species. Afterward, Cope named the species Ornithochirus umbrosus and Ornithochirus harpyia based on these specimens, respectively. He attempted to assign them to the pterosaur genus Ornithocheirus, but misspelled the name forgetting the 'e'. Cope stated that Pterodactylus was chiefly from the Jurassic period, so it was unlikely that the species from the Niobrara Formation, which is from the Cretaceous period, belonged to Pterodactylus, therefore, he assigned both O. umbrosus and O. harpyia to the genus Ornithocheirus, even though misspelling it. These two species however, were differentiated by Cope based only on size, he pointed out that the wingspan of O. umbrosus measured nearly 7.6 meters (25 ft), while the wingspan of O. harpyia measured 5.5 meters (18 ft). He additionally indicated, more conservatively, that the skulls "were slender and the teeth indicated carnivorous habits". In his description of these species, he stated that Ornithochirus harpyia was around the same size and probably synonymous with "Pterodactyhts oweni", but because this species was preoccupied, his Ornithochirus harpyia should replace it. Anonymously, Marsh replied to Cope's paper describing O. umbrosus and O. harpyia, and noted that these species were junior synonyms of Pterodactylus ingens and Pterodactylus occidentalis, respectively. This is because Marsh's second publication, the one where he renamed "P. oweni" as P. occidentalis, was published 5 days before Cope's publication of O. umbrosus and O. harpyia, and thus Marsh's publication had priority over Cope's. Later, in 1875, Cope had repeated his description of the type specimens of both Ornithochirus umbrosus and Ornithochirus harpyia, where he included slight corrections. He accepted that his O. harpyia was a junior synonym of Marsh's Pterodactylus occidentalis, but he had reassigned O. umbrosus as Pterodactylus umbrosus, thus becoming a species of Pterodactylus, even though he had noted before that species from the Niobrara Formation unlikely belonged to Pterodactylus due to their different age, this also meant that he still considered O. umbrosus as a separate species. Re-evaluation by later scientists had supported Marsh's case, and also found that Cope's assertion of O. umbrosus as larger in size than Pterodactylus ingens was incorrect, this is due to a comparison of the diameters of the distal condyles of the syntypes of both species, which showed that they were nearly the same size.^[5]^[7]

Naming[edit]

Specimen YPM 1177, the holotype of Pteranodon. It is interpreted as a female individual due to its short cranial crest

In 1874, Marsh had hired many fossil collectors to work in the exposures of the Niobrara Formation. More fossil material was collected in the next 6 years, among these include specimen YPM 1177, which was discovered in 1876. YPM 1177 is a well-preserved and nearly complete skull, this specimen revealed that the pterosaur species from the Niobrara Formation were different from every other pterosaur species that were then known, this is because it possessed features such as toothless jaws and a cranial crest that projected from the back of the skull. These features weren't seen in any of the pterosaurs known at the time. Due to this staggering new discovery, Marsh coined a new genus and species called Pteranodon longiceps.^[5]^[8] The generic name is derived from the Greek words πτερόν (pteron, meaning "wing"), ἀν (an, meaning "without"), and ὀδούς (odous or odont, meaning "tooth"), in reference to the toothlessness of its jaws,^[9] while the specific name, longiceps, derives from the Latin words longus (meaning "long") and ceps (meaning "headed").^[10] He assigned this species as the type species of the genus, and subsequently, he reassigned all known North American species of Pterodactylus to Pteranodon, distinguishing them only by their toothlessness. He considered P. longiceps to be somewhat larger than P. occidentalis, but smaller than P. ingens. Additionally, he indicated skull lengths of more than 1.2 meters (4 ft) and wingspans reaching 7.6 meters (25 ft).^[5]^[3]

Other discoveries[edit]

In the same paper publishing P. longiceps, Marsh named another species, Pteranodon gracilis, based on a notarium (bone consisting of fused vertebrae in the shoulder) that had both scapulocoracoids (union of the scapula (shoulder blade) and coracoid), he erroneously identified this specimen as a pelvis. Eventually, Marsh had recognized his mistake, and without mentioning his misidentification of the notarium, he placed P. gracilis in a new genus he called Nyctosaurus. The reason why is because the coracoid and scapula in P. gracilis were not co-ossified (grown as one with the other) as in other species Pteranodon.^[5]^[3]^[11] Marsh had also named two additional species thereafter, one of them was Pteranodon comptus, which was based on fragments of three skeletons including what he had identified as two distal ends of a metacarpal, as well as two sacral vertebrae. These fossil remains were actually the distal ends of tibiae belonging to a small Pteranodon individual and dorsal vertebrae of Nyctosaurus. The other species Marsh named as a very small one, Pteranodon nanus, based on fragments of the jaw, a partial notarium, a humerus, and a scapulocoracoid. Thi specimen was placed in Pteranodon because its scapulocoracoid was fully co-ossified, as in other Pteranodon species Altogether, Marsh had named six Pteranodon species that ranged in size from the very small P. nanus to the very large P. ingens. Morphological characters were noted for each of the species, however, it is clear that Marsh used the size of the species as the main difference between them.^[5]

Revising species[edit]

In 1892, Samuel Williston examined the classification of Pteranodon by Marsh, and he noticed that back 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",^[12] and 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, and he reassigned the species P. ingens as Ornithostoma ingens due to this conclusion.^[13]^[5] Interestingly, he also reassigned Cope's Ornithochirus harpyia into Ornithostoma, creating the new combination Ornithostoma harpyia.^[5] In 1901 however, German paleontologist Felix Plieninger pointed out that "Ornithostoma" had never been scientifically described or even assigned to a species name until Williston's work, and therefore had been a nomen nudum and could not beat out Pteranodon for naming priority.^[14]^[3] Williston accepted this conclusion and went back to calling the genus Pteranodon. Both Williston and Plieninger however, were incorrect, because unnoticed by both of them was the fact that back in 1891, Seeley himself had finally described and properly named Ornithostoma, assigning it to the species named as O. sedgwicki.^[5]^[15] 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.^[13]^[5]

Williston was also the first scientist to critically evaluate all of the Pteranodon species classified by Cope and Marsh. He did agree with most of Marsh's classifications, but a few exceptions were made.^[3] First, he did not believe that P. ingens and P. umbrosus could be considered synonyms, which even Cope had come to believe. Williston considered both P. velox and P. longiceps to be dubious; the first (P. velox) was based on non-diagnostic fragments, and the second (P. longiceps), though known from a complete skull, probably was a synonym of one of the other previously named species.^[5] In 1903, Williston revisited the question of Pteranodon classification, and revised his earlier conclusion, in which he stated that there were only three species of Pteranodon, instead of seven. He also 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) primarily based on the shape of their upper arm bones.^[16] He also followed his first conclusion of P. longiceps being a synonym of either P. velox or P. occidentalis based on its size, but he did not specify to which of the two species would be synonymized.^[16] Later that year, paleontologist George Francis Eaton became the first scientist to publish a more detailed description of the entire Pteranodon skeleton. He used his findings to revise the classification of this genus, once again based on a better understanding of the differences in pteranodontid anatomy.^[5] Eaton found that most of the differences in bone shapes could be easily explained by the pressures of fossilization, and concluded that none of the 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. He assigned the different sized skulls into different species according to their size, but in the end, Eaton only recognized three valid species: P. occidentalis, P. ingens, and P. longiceps.^[17]^[18] In 1910, Eaton assigned specimen YPM 1164 as the type species of P. occidentalis, and stated that back then, Marsh had observed the form of the jaws of P. occidentalis in a fragmentary skull of specimen YPM 1179, and from his notes it is evident to also consider this specimen as the type, thus assigning it as the "type skull" of P. occidentalis.^[19] This was incorrect however, because the remains found of YPM 1179 were not collected until after the initial publication of P. occidentalis in 1871 by Marsh, which was published under the preoccupied name "Pterodactylus" oweni.^[19]

In the same year as the assignments of YPM 1164 and YPM 1179, Eaton had given credit to Williston's conclusions after he had criticized them back in 1903, this was due to the incompleteness and uncertainty of the specimens. Eaton also limited his discussions of the skeletons of Pteranodon afterwards.^[20] In doing so, he noticed one issue: he couldn't trace a fibula in the preserved specimens, which was stated by Williston back then. Williston then mentioned that he found distinct remains of the fibula fused with the tibia, and therefore, he conducted experiments in 1912 using clay models of bones to help determine the effects of crushing and flattening on the shapes of the arm bones that Eaton had used in his own classifications.^[20]^[21] In 1920, paleontologist Carl Wiman had noted that in his description of the specimens purchased by fossil collector Charles Hazelius Sternberg, a tibia of which he figured to belong to Pteranodon included a remnant of a fibula, this meant that at least several specimens had this state of preservation.^[20]

In 1952, paleontologist George Fryer Sternberg, the son of Charles H. Sternberg, unearthed several fossil remains from the lower Niobrara Formation that looked similar to those of P. longiceps, though the crests were set upright and in a slightly different position. In 1958, Sternberg and paleontologist Myrl V. Walker published a study about the peculiar find.^[22] In 1966, American paleontologist John Christian Harksen assigned the specimens found as a new species called Pteranodon sternbergi, due to its distinct upright crest.^[23] This however, complicated the situation even more, prompting another revision of the genus in 1971 by Halsey W. Miller.^[24] Miller concluded that all Pteranodon species except P. longiceps and P. sternbergi (the ones based on skulls) must be considered nomina dubia and abandoned due to impossible determination of crest shape for all of the species based on headless skeletons. This conclusion however, was mostly ignored at the time, and paleontologists still assigned previously found specimens to new species.^[3] The skull that George Eaton had thought to belong to P. ingens was later placed in a new species called P. marshi by Miller, and the skull he assigned to P. occidentalis was reassigned as P. eatoni, resulting in two new species.^[5] Miller had also recognized another species based on a skull with a crest similar to that of P. sternbergi, he reassigned its specimen as a new species called P. walkeri. This would contradict his first conclusion of considering all Pteranodon species that weren't based on skulls as nomina dubia.^[3] Miller also created three categories or subgenera for them due to the tangle of names; P. marshi and P. longiceps were placed in a subgenus known as Longicepia, though this was later changed to simply Pteranodon due to the rules of priority, meaning that Pteranodon was both a genus and a subgenus at the time.^[25] P. sternbergi and P. walkeri, which specialized in having the upright sagittal crests, were given the subgenus Sternbergia, but was later changed to Geosternbergia, because Sternbergia was found have been named to a genus of flower, and therefore had been preoccupied at the time.^[26]^[27] Finally, Miller named the subgenus Occidentalia for P. eatoni, due to its skull being formerly associated with P. occidentalis. He further expanded the concept of Pteranodon to include Nyctosaurus as a fourth subgenus, and considered these to be an evolutionary progression, with the primitive Nyctosaurus, at the time thought to be crestless, giving rise to Occidentalia (with a small crest), which in turn evolved to Pteranodon with its long backwards crest, and finally leading to Geosternbergia with its large, upright crest.^[24] In 1972, Miller followed Eaton's assignments of specimens as the types of dubious species.^[19] He accepted that specimen YPM 1164 would be the type of P. occidentalis, though assigning YPM 1179 as the type of P. eatoni. Following Eaton yet again, Miller also accepted specimen YPM 1175 as the type of P. ingens, while listing specimen YPM 1176 as the type of P. velox, to which Eaton did not state a number.^[19] Both Miller and Eaton however, made several mistakes in their studies concerning which specimens Marsh had assigned to which species, and most scientists disregarded his work on the subject in their later research.^[28]^[29]

Later revisions[edit]

In 1975, paleontologist Ross S. Stein published a revision that essentially returned to Marsh's original classification scheme, most notably sinking P. ingens as a synonym of P. longiceps.^[30] Later, in 1978, German paleontologist Peter Wellnhofer followed the incorrect species list by Miller and Eaton, and recognized both P. occidentalis and P. eatoni as valid based on postcranials, while also listing the specimens YPM 1164 and YPM 1179 as their type respectively. However, Wellnhofer argued the inclusion of Nyctosaurus being a subgenus of Pteranodon.^[19]^[5] In 1984, paleontologist Robert Milton Schoch from the Yale Peabody Museum published a revision of the type specimens of both Pteranodon and Nyctosaurus.^[19] Schoch stated that the species P. longiceps and P. marshi should be considered junior subjective synonyms of P. ingens, the dubious species P. comptus as a junior subjective synonym of P. velox, and the species P. eatoni as a junior subjective synonym of P. occidentalis. Schoch then designated specimen YPM 1170 as the lectotype of P. ingens due to the it being the most complete specimen. He also mentioned that back in 1972, Miller had accepted Eaton's assignment of specimen YPM 1175 as the type of P. ingens, but stated that this wouldn't be case due to the fact that YPM 1175 was collected after Marsh's initial description of P. ingens. Schoch also noted that Miller had stated that the cataloged bones of YPM 1175 were found in two different localities, Schoch however, hadn't found a single evidence to prove this statement.^[19] Later, in 1994, pterosaur researcher S. Christopher Bennett made an extensive revision of the species of Pteranodon, and only recognized two species as valid: P. longiceps and P. sternbergi (or Geosternbergia sternbergi), and regarded the other species as nomina dubia based on inadequate materials, or junior synonyms based on specimens of different size, sex, or age than the type specimens of the valid species.^[5]

Description[edit]

Size[edit]

Pteranodon specimens are extremely well represented in the fossil record, with at least 1,200 identified, which is more than any other pterosaur. Detailed descriptions of their anatomy and analysis of their life history have been debated since, and even with the amount of specimens found, more than half still lack completeness, so paleontologists base upon the better known specimens to extract data.^[5]^[11]

Marsh initially estimated the wingspan of Pteranodon around 7.6 meters (25 ft) following his publication of the genus, this made Pteranodon the largest known pterosaur back then, and no other wingspan estimates could challenge it. This was later downsized by Eaton in 1910 however, giving a lower estimate of about 6.8 meters (22 ft). In 1910, Eaton concluded that factoring flexions to the wing bones would give a more realistic wingspan estimate, instead of just adding the length of both wing bones snd shoulder width.^[31] The conclusion of Eaton however, resulted in accuracy complications, since no methodological details were provided.^[3] The description of Pteranodon sternbergi (now known as Geosternbergia) in 1966 by Harksen, also resulted in several complications for size conclusions, as the skull was the only accurate basis back then.^[23] Harksen had estimated a wingspan of about 9.1 meters (30 ft) based on the nearly complete skull, making it the pterosaur with the largest wingspan estimate known at the time, even larger than the recorded estimate by Marsh to P. longiceps, which was about 7.6 meters (25 ft).^[3] Later, in 1994, paleontologist Christopher Bennett followed the size conclusion of Eaton in 1910, but he did not consider the conclusion by Harksen in 1966.^[5] He stated that Pteranodon would still be a valid taxon, and in 2001, Bennett made a more comprehensive review with the known material of Pteranodon, and suggested that its wingspan estimates would have fared better for later studies rather than its taxonomy.^[32] In his review, Bennett kept the 6.8 meter (22 ft) wingspan estimate for P. longiceps, but rejected the 9.1 meter (30 ft) estimate for P. sternbergi, this is due to his agreement with Eaton, in which the wingspan estimates should allow flexions to the wing joints, while excluding the shoulder width when measuring the length of the wing bones. Bennett also suggested that the largest specimen of Pteranodon was not the skull that belonged to P. sternbergi, but instead, he pointed out that a few reported specimens unearthed in the Pierre Shale Formation were found to have been proportionally larger than any other known Pteranodon specimens, these specimens were estimated to have had a wingspan of about 7.25 meters (23.8 ft) based on flexions added to wing joints, while also excluding the shoulder width.^[3] If this statement is correct, then it would most likely be the largest known Pteranodon specimen.^[5] Recent studies however, conclude that this specimen may have belonged to the separate species Geosternbergia maysei instead.^[27]

Average wingspan estimates for Pteranodon had since decreased, adult males are estimated to have had a wingspan of only about 5.6 meters (18 ft), and adult females were yet smaller, and according to several analyses, their wingspans only measured about 3.8 meters (12 ft).^[5] The largest specimen of Pteranodon longiceps was unearthed in the Niobrara Formation, and was estimated to have measured about 6.25 meters (20.5 ft) from wingtip to wingtip, far shorter than initial estimates.^[3] In 2017, a much smaller specimen was uncovered in the Niobrara Formation, this represented an individual measuring only about 1.76 meters (5.8 ft), which is approximately 45 percent smaller than the smallest previously known specimen, but does not differ in morphology from the larger specimens. It is thought that this specimen belongs to a young juvenile because they are otherwise unknown or rare in the Smoky Hill Chalk Member of the Niobrara Formation, and they must have occupied different environments and ecological niches compared to adults. Pteranodon therefore exhibited ontogenetic niches, and evidence is also presented that most other pterosaurs such as Rhamphorhynchus, Pterodactylus and Anhanguera may have exhibited various ontogenetic niches similar to those of Pteranodon. In 2018, Christopher Bennett published a conclusion about ontegenetic niches of Pteranodon and related genera, in which he suggested that the diversity of pterosaur taxonomy was rather low, similar to that of crocodilians.^[33]

Several methods have been used to estimate the mass of large male specimens, which have also been considered notoriously unreliable, producing a wide range of estimates from as low as 20 kilograms (44 lb), to as high as 93 kilograms (205 lb). Published in 2010, a review of pterosaur size estimates concluded by researchers Mark Witton and Mike Habib demonstrated that the largest wingspan estimates of Pteranodon are almost certainly incorrect given the total volume of a Pteranodon body.^[34] Witton and Habib considered the methods used by researchers who obtained smaller mass estimates equally flawed. Most have been produced by scaling up modern animals such as bats and birds up to the size of Pteranodon, despite the fact that pterosaurs have vastly different body proportions, as well as soft tissue anatomy compared to any living animal today.^[34]

Skull and beak[edit]

Comparison between different pteranodontian skulls, including the ones belonging to *Pterandon longiceps* (middle left), the one belonging to *Pteranodon* sp. (lower left), and the one belonging to the dubious species *P. ingens* (lower right)

When Pteranodon was discovered, the skull was yet to be known, and therefore paleontologists based upon other pterosaur genera (most notably Pterodactylus) to make early reconstructions of the animal, in which Pteranodon had teeth, and lacked the cranial crest. When the first skull of Pteranodon was unearthed and then analyzed, paleontologists had understood more about the skull anatomy of Pteranodon, and concluded that it was unique compared to European pterosaurs such as Rhamphorhynchus.^[35] This is mainly due to the fact it lacked teeth, and had a distinctive crest on its head.^[32] The cranial crest of Pteranodon is the most distinctive characteristic of the animal, and consists of skull bones 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. Males from the species Pteranodon sternbergi (now known as Geosternbergia), likely had a more vertical crest with a broad forward projection, while their later descendant species, Pteranodon longiceps, evolved a narrower, more backward-projecting crest.^[11] Females of both species however, bore smaller, rounded crests. These crests were probably mainly display structures, specially in males, though several conclusions of paleontologists led to the idea that the crests may have had other functions as well.^[36]^[11]

Unlike earlier pterosaurs such as Rhamphorhynchus and Pterodactylus, Pteranodon had a toothless beak that was made of solid, bony margins that projected from the base of the jaws, similar to modern-day birds. The beaks also had subparallel dorsal and ventral margins, as well as slender and thin, but sharp points. The maxilla was found to be longer than the mandible, and was curved upward, this was more exaggerated in males than in females.^[37] One specimen in particular (UALVP 24238) has been found to possess a distinctive curvature than in other specimens, which likely corresponded with the beak widening towards the tip. While the tip of the beak is not known in this distinct specimen, the level of curvature suggests it would have been extremely long. The unique form of this specimen's beak led to a genus reassigning in 2010 by Brazilian paleontologist Alexander Kellner, in which the genus would be called Dawndraco.^[27] A recorded skull length of Pteranodon based on several skull fragments was about 1.3 meters (4.3 ft), this was concluded by Marsh with his publication of P. longiceps back in 1876.^[3]

Shoulder girdle[edit]

The shoulder girdle of Pteranodon was found with a strong structure, and consists of the scapula, the coracoid and the sternum. It is found to project obtusely in front of the articulations of the animal. The sternum of Pteranodon had thin lateral margins which are thin, and have three emarginations where four articular projections separated. According to Williston, the sternal bones were small and pointed, and could have only given attachment to slender ribs. He also stated that the lateral borders of the sternum were parallel with the longitudinal axis of the bone; the posterior border, while not preserved, resembled generally that of Nyctodactylus, a junior synonym of Nyctosaurus.^[16]^[31] The posterior border was also nearly straight, though it might have been gently concave or convex. In Eaton's study of the osteology of Pteranodon, specimen YPM 2546 was stated to have a lower surfaced sternum, while it was also referred to belong to a large animal, about nine-tenths the size of YPM 1175, a specimen that belongs to the large species P. ingens. Specimen YPM 2546, which has a nearly complete restoration of its sternum, was suggested that its four lateral projections would have been an attachment for its sternal ribs; Eaton also found a fifth pair of projections that may have been for articulation with a fifth pair of sternal ribs. A small vacuity was present in the midline of the midline of the sternum, close to the posterior border, and immediately at the rear of the vacuity, a pair of closely approximated articular projections was also seen. These projections may have probably served as a connection with the abdominal ribs. Vertically, the manubrium was much deeper than widely, and the sharp inferior edge continued backward middle of the broad part of the sternum, similar in shape to a rudimentary keel.^[31]

In YPM 1175, the scapula and coracoid were united, and were defective behind and below the glenoid. The right scapula and right coracoid of specimen YPM 1181 had a deep and narrow depression that lies immediately behind the glenoid surface, this depression is presumably the coracoidal foramen as seen unmistakably, but no other specimen showed clear evidence of this feature, so there is no specific reason for supposing this in other species. A large oval facet was present in the distal extremity of the scapula, and was placed obiquely to the long axis, while also obliquely to the transverse axis of the body, this indicates that the facet was not only directed outward and downward, but also more or less forward.^[31] The glenoid articulation is deeply concave from above downward, convex from side to side, and bounded both above and below by a prominent ridge that was much stronger than the upper one, and the ridge itself is located on the inferior border. An articular process arised from the scapula, and reaches the anterior surface of the coracoid, to which it was somehow joined, and as stated by Williston, this fusion is called "coracoscapula", and it is described as U-shaped.^[38] The articular process incloses a small, oval foramen just located at the back of the middle section of the glenoid surface, and the diameter of the foramen is about 12 millimeters (0.47 in).^[31]

Wings[edit]

Pteranodon had wings very similar in build to the modern-day albatross, and it has been suggested that it would have flown similarly. This is based on the fact that Pteranodon had a high aspect ratio (wingspan to chord length) and low wing loadings, similar to modern-day soaring birds such as the mentioned albatross. The aspect ratio of Pteranodon is estimated to be about 9:1, while the one estimated for albatrosses is 8:1.^[39]^[40]

The structure of the wings also suggest that Pteranodon flew very long distances without flapping constantly, similar to the related ornithocheirids, which have also been identified with this flight technique.^[41] The geological formations where Pteranodon has been discovered were stated that these were covered by a large inland sea, which formed part of the Western Interior Seaway, meaning that Pteranodon would have lived, hunted, and most of the time, flown near the coast.^[42] Early reconstructions of Pteranodon were made during the first quarter of the 20th century, where paleontologists carried the wing-membranes down to the lower hindlimbs or ankles. Reconstructions of several other pterosaurs such as Dorygnathus and Pterodactylus have also resulted in their brachiopatagium extending down to their lower hindlimbs, therefore looking somewhat bat-like.^[43] Several other reconstructions however, have found that pterosaurs such as Pteranodon had ther wing-membranes extended only until their hips, and as a result, it is associated with the hindlimb at about the level of the knee.^[43]^[44]

Forelimbs[edit]

Pteranodon had unusually long forelimbs compared to other pterosaur genera, this may be, yet again, another indication that Pteranodon was more advanced, or at least more derived.^[41] The metacarpals of Pteranodon were more than twice the length of the humerus, and such proportions can only be seen in one other group of pterosaurs: the azhdarchids, which also possessed very large metacarpals in comparison to their humeri.^[41] The wing fingers of Pteranodon occupied over 60 percent of the wing, which is an impressive proportion only seen in the more advanced genera such as other pteranodontids and azhdarchids. Analyses on ornithocheirids led to the idea that they most likely possessed comparable metacarpal sizes to those of Pteranodon, but not as large.^[41]^[32] British paleontologist Mark Witton concluded that the first, second and third metacarpals of Pteranodon have lost contact with the carpus, but still possessed three small fingers at the distal endings.^[41] Back in 1911, Samuel Williston made a revision of the wing-finger of the pterosaurs Pteranodon, Nyctosaurus and Pterodactylus, where he stated that the more adavanced and larger pterosaurs had either lost or reduced their fifth In his revision of Pteranodon and Nyctosaurus, he stated that the three carpal bones remained along with a proximal one, as a result, doubtlessly fused radiale, intermedium, and ulnare were found; a lateral carpal for the support of the pteroid, which, as Williston stated, may be either the centrale or the first carpale was also found, and finally, he noted a distal finger which represented the fourth carpale alone, therefore it would have been highly probable that the carpale is the fourth, and that it supports its proper finger, meaning that the fifth had either migrated to a more anterior carpale, or was potentially lost.^[45]

Vertebral anatomy[edit]

Vertebrae remains of Pteranodon had many distinguishing traits compared to other pterosaur vertebrae, some of these include neural spines, which were generally tall and spikelike; plate-like bony ligaments strengthening the vertebrae above the hip were also found in some specimens. Similar to its close relatives, Pteranodon also had a relatively long and robust neck, and it was proportionally longer than the torso itself.^[46]^[37]

Pteranodon had nine cervical vertebrae, counting the atlas and the axis as the first two units of the vertebral column. All of the Pteranodon specimens had the atlas and axis co-ossified, but in specimens YPM 1175 and YPM 1177, it is not possible to trace readily the limits of the theoretical elements that composed the fused vertebrae. The third, fourth, fifth, sixth and seventh cervicals are similar in appearance in terms of general form, their only slight difference is seen in their lengths. The natural sequence of the cervicals of Pteranodon can also be seen without any doubt. Measurements of the cervical centra of YPM 1175 have been done by Eaton in 1910; following him, the third cervical centrum measured 61 millimeters (2.4 in), the fourth 67 millimeters (2.6 in), the fifth 88 millimeters (3.5 in), the sixth 76 millimeters (3.0 in), and the seventh 65 millimeters (2.6 in). With these measurements of the cervical centra in mind, it would appear that the third cervical was the shortest of the five vertebrae, then the fourth and fifth successively increasing in length, but afterwards, the sixth and seventh were decreasing, and the size of the seventh cervical was reduced comparably to the fourth. While this sequence is present in YPM 1175, it is also substaintiated in part by YPM 2594, where the third cervical is anything but greater in size than the united atlas and axis, which is where it is remained attached. Pneumatic canals have found to lighten the cervical vertebrae to where they enter the centra.^[31]^[47]^[32]

Nearly all the dorsal vertebrae of Pteranodon are involved in one or two heavily fused girder-like structures called the notarium and synsacrum.^[48] The first articular facet joint that supports the ribs begins at the angles, and runs backwards about 1.27 centimeters (0.042 ft). According to Williston back in 1897, the articular facet joint is of considerable thickness, and might have served as an attachment for the co-ossified ribs, and the ribs themselves are connected to the consolidated dorsal vertebrae of the animal.^[38] In 1910, Eaton found that the neural arch of the vertebrae of Pteranodon was proportionally smaller than that of the close relative Nyctosaurus. In a posterior view of the neural arch, the convex oval termination of the centrum appears to be transversely more produced than the one seen in Nyctosaurus, and the supplementary articular processes, while not confluent, remained separate and distinct, similar to the cervicals. An extention of the notarium of Pteranodon is formed by eight dorsal vertebrae which are bound together by paired ossifications. The first dorsal vertebra is found to have the largest centrum; its length and width are about equal, and its oval articular "cup" as well as the anterior articulating facets resemble those of the last cervical of Pteranodon.^[31]^[47] A fusion of vertebral ribs and dorsal vertebrae, and dorsal vertebrae themselves is seen in Pteranodon, as well as in the pterosaurs Dsungaripterus and Tupuxuara. This may likely reflect a response to the structural demands placed on these regions by stresses transmitted through the body during flight, and as suggested, it might have immobily rendered the dorsal portion of the thorax, though did not completely restrict thoracic movement.^[49]

Tail and caudal[edit]

The last few vertebrae were fused into a long rod that extended until the beginning of the animal's tail. The tail of Pteranodon was relatively short compared to earlier genera such Rhamphorhynchus, which led to the idea that the later genera such as Pteranodon used their tail less often. The entire length of the tail was about 3.5 percent the size of the wingspan, and was up to 25 centimeters (9.8 in) in the largest males, which is not that impressively large in terms of tail-to-wingspan ratio.^[50]^[37] Short tails were also seen in the contemporary ornithocheirids such as Ornithocheirus, and were very similar in structure to that of Pteranodon. Other related such as Anhanguera are also known for several tail remains, and a few synapomorphies between Anhanguera and Pteranodon were found, the most notable synapomorphy was the structure of their short tail, and both of these pterosaurs also had broad caudal vertebrae.^[50]^[51] In comparison to the related genus Dawndraco, the caudal vertebrae of Pteranodon were overall shorter. However, it is unknown if the distal caudals of Dawndraco also extended into a rod-like structure.^[27]

Hindlimbs[edit]

In contrast to the forelimbs of Pteranodon, its hindlimbs were relatively short compared to the overall size of the body. Pteranodon, and its relative Nyctosaurus, had the shortest hindlimbs of any pterosaur genera, in terms of hindlimb-to-body ratio, only about 20 percent the size of the wing.^[41]

Some remains of the feet of Pteranodon were also found, and are enough for paleontologists to determine how their size were. Contrary to the small feet seen in earlier pterosaurs such as istiodactylids and boreopterids, the feet of Pteranodon were found to have been similar to the larger feet of ornithocheirids. Another feature that Pteranodon had was that it only bore four toes instead of five, a common synapomorphy also seen in most of the later genera. The large feet of Pteranodon appear to have helped it take off from the ground, acting like strong propulsors, while flapping repeatedly before gaining control of a soar flight.^[41]^[11]^[32]

Classification[edit]

Evolution and timespan[edit]

Fossils of Pteranodon are primarily known from the Niobrara Formation of the central United States. Broadly defined, Pteranodon existed for more than 4 million years, from the late Coniacian to the early Campanian stages of the Late Cretaceous period.^[5] 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 the fossils in this formation, demonstrating that the species P. sternbergi, now considered to belong to the separate genus Geosternbergia, existed in the formation from 88 to 85 million years ago, while the type, and potentially only species, P. longiceps, existed between 86 and 84.5 million years ago.^[42]

In the early 1990s, Bennett noted that the two major morphs of pteranodontids 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 one time, and the species P. sternbergi (or G. sternbergi) in all likelihood was the direct ancestor of the type species, P. longiceps, or more specifically, the genus Geosternbergia would have been the dirtect ancestor of Pteranodon.^[5]^[29]

Phylogeny[edit]

Studies on Pteranodon specimens have suggested that it was a distant relative of the ornithocheirids such as Ornithocheirus due to the similar diet, as well as the flight techniques and features. A genus called Anhanguera for example, had broad caudal vertebrae that was similar to that of Pteranodon.^[37]^[52]^[53]

Phylogenetic analyses have placed the type species of Pteranodon, P. longiceps, within the family Pteranodontidae, as the sister taxon of the species P. sternbergi, which is now reassigned as Geosternbergia sternbergi. The recently named genus Tethydraco has been included within the family Pteranodontidae in an analysis presented by Nicholas Longrich et al. in 2018, and placed as the sister taxon of both P. longiceps and P. sternbergi, but within a more basal position.^[54] The clade Pteranodontia was once thought to have been the more inclusive clade containing the pteranodontids, the ornithocheirids, and their descendants, but recent analyses have concluded that the clade Pteranodontoidea would have been the more inclusive group, while restricting Pteranodontia with the families Pteranodontidae and Nyctosauridae.^[54]^[55]^[56]

Topology 1: Andres and Myers (2013).^[57]

Pteranodontia

Nyctosauridae

Alamodactylus byrdi

Pteranodontoidea

	Pteranodon longiceps

	Pteranodon sternbergi

Istiodactylidae

Longchengpterus zhaoi

Nurhachius ignaciobritoi

Liaoxipterus brachyognathus

	Istiodactylus latidens

	Istiodactylus sinensis

Lonchodectes compressirostris

Aetodactylus halli

Cearadactylus atrox

Brasileodactylus araripensis

	Ludodactylus sibbicki

	Ornithocheirae

Topology 2: Longrich and colleagues (2018).^[54]

Pteranodontoidea

Ornithocheiromorpha

Pteranodontia

Pteranodontidae

Tethydraco regalis

	Pteranodon longiceps

	Pteranodon sternbergi

Nyctosauridae

Alamodactylus byrdi

Volgadraco bogolubovi

Cretornis hlavaci

	Alcione elainus

	Simurghia robusta

Muzquizopteryx coahuilensis

	Barbaridactylus grandis

	Nyctosaurus lamegoi

	Nyctosaurus nanus

	Nyctosaurus gracilis

Paleobiology[edit]

Flight and aerodynamics[edit]

The flight ability of Pteranodon was intensively more than pterosaurs, and the flight techniques that Pteranodon used were similar to those of modern-day albatrosses, which consisted in long distance flights and rarely flapping.^[41] Flight and wing analyses of Pteranodon had been made throughout its history.^[58] In 1971, Heptonstall concluded that the species P. ingens (now considered a synonym of P. longiceps) had a weight of about 22.7 kilograms (50 lb), which was sufficient to enable the animal to bank to an angle of 75 degrees and allowed a minimum horizontal turning circle of radius 11.4 meters (37 ft).^[40] Flying speed and sinking speed relationships have also been computed by Heptonstall, and a comparison was made between the performance of fulmars, a typical man-made glider, and P. ingens. In the comparison, Heptonstall concluded that P. ingens would have had difficulties hovering, this is due to the volume of muscle required, and as a result, P. ingens would be unable to take off without the assistance of a prevailing wind. Heptonstall also concluded that the cranial crest is shown to have been adapted for controlling yawing movements while reducing the torque on the neck muscles, therefore Pteranodon was also well suited to thermal soaring.^[40]

Later, in 1974, Cherrie Bramwell and George R. Whitfield published an extensive analysis of the biomechanics of Pteranodon. In their analysis, they concluded that when flapping, the humerus of Pteranodon can move down (at the lowest point) 25 degrees below its horizontal position, and it can raised (at the highest point) 70 degrees above its horizontal position. Bramwell and Whitfield also considered that Pteranodon had a specialization for gliding instead of flapping, this is due to their conclusion that the glenoid cavities of Pteranodon had their upper and lower surfaces set at an angle to each other, and when combined with the ridged articular head of the humerus, a lock in one position is formed. When articulated in this way, the humerus of Pteranodon is directed upwards 20 degrees, and positioned 19 degrees backwards, therefore, Bramwell and Whitfield assumed that this would have been the natural position for gliding. Wind tunnel experiments were also made in the analysis, where Brawmwell and Whitfield used head models of Pteranodon with and without a crest. The head model without a crest showed that the couple rises rapidly with an increasing angle, to a maximum of 12.5 newton-meters (9.2 lb⋅ft) at a 55 degree turn, and then falling gradually to zero when reaching an angle of 180 degrees. The crest of Pteranodon on the other hand, had little effect at small angles, but beyond 70 degrees it begins to balance the beak of the animal, and at angles above 100 degrees, the couple is found to be very small. This unexpected result suggests that at small angles the crest lies in the turbulent wake behind the head, while also blanketed. At larger angles however, it balances the beak of the animal. A calculated 100 grams (3.5 oz) of muscle is just sufficient to resist the loads on the head with the crest at the most difficult angle, about 60 degrees. Without the crest however, 100 grams (3.5 oz) of muscle is too weak at angles above 100 degrees, and at least twice as much muscle would be needed to hold the head at an angle of 130 degrees. If Pteranodon had even less efficient muscles, even more mass of muscle would have been needed, and since there are two neck muscles, the total mass must have been 200 grams (7.1 oz). Additionally, the crest weighs about 30 grams (1.1 oz), so clearly, the crest is lighter than the extra neck muscle that would have otherwise been required. In this way, the crest of Pteranodon is mass-saving by allowing mass reduction of the neck muscles. The head is also considered a useful rudder, while the crest contributes little to this, as it is located very near the center of gravity of the animal. Turned through 90 degrees, the head would have also been a good air brake, contributing drag that is equal to that of the rest of the animal, and about half this drag is due to the crest.^[47]^[59]

Another flight analysis of the species P. ingens was conducted by Ross Stein in 1975. In the analysis, Stein considered that Pteranodon would have been better suited for soaring or gliding rather than a flapping flight, as concluded in previous analysis. He also concluded that the minimum flight velocity of P. ingens was calculated to have been about 4.5 meters (15 ft) per second, while the maximum was around 15 meters (49 ft) per second. Along with this, the wing-beat cycle of Pteranodon would have been about 1 stroke per second, and therefore it would have allowed an unassisted takeoff.^[60]^[58]

Terrestrial locomotion[edit]

^[47]

Respiration[edit]

Studying and analyzing the respiratory system of different pterosaurs, paleontologists have seen that the ribcage, including that of the early Eudimorphodon, consists of a large ossified sternum and distinct vertebral and sternal ribs; the sternal ribs of well preserved examples of Pteranodon bore elaborate dorsal and ventral processes termed as sternocostapophyses. These projections likely functioned as levers that increased the moment arm for the intercostal muscles, and conferring an enhanced capacity to move the sternal ribs during lung ventilation. Similar to the uncinate processes found in birds and maniraptoran theropods, sternocostapophyses have an analogous function in lung ventilation. Another similarity found in sternocostapophyses is that the leverage provided by the sternocostapophyseal projections of Pteranodon and other pterosaurs likely lowered the work of breathing of the intercostal musculature, and have resulted in costal and sternal displacement. Unlike the uncinate processes of birds however, the mechanical leverage provided by the sternocostapophyses likely differed from that conferred by the uncinate processes of maniraptoran theropods and birds, and the greatest mechanical leverage would have been provided in the ventral region rather than in the dorsal thoracic. Yet another dissimilarity found in pterosaurs such as Pteranodon that is not seen in birds is that the sternocostapophyses are located on the sternal ribs rather than the vertebral ribs, and generally, there are multiple sternocostapophyseal projections per sternal rib, rather than a singular uncinate process.^[49]

Skeletal pneumatization[edit]

Pneumatization is a special feature seen in several pterosaur genera such as Pteranodon; pneumatic foramina were also found to have been reliable indicators of postcranial skeletal pneumatization. Pneumatic bones in pterosaurs have been concluded to be analogous with that of modern-day birds, while at the same time being associated with the presence of air sac systems, to which allows the invasion of air inside the bone. This feature shows the possibility of how pterosaurs developed the ability to fly actively.^[61]^[62] Within the analyzed specimens of Pteranodon, a pneumatic foramen was found on the base of the prezygapophysis (superior articular processes), in a similar position to the primitive non-pterodactyloids such as Rhamphorhynchus; in YPM 2440, a specimen belonging to Pteranodon, only the fourth cervical vertebra has appeared to have some variation in the position of the foramen, and as stated by Bennett in 2001, the foramen was possibly originally positioned on the centrum.^[32]^[61] Paleontologists Richard Buchmann and Taissa Rodrigues found that in mid-cervical vertebrae, the dorsal presence of pneumatic foramina to the neural canal has appeared three times in azhdarchoids, in specimen AMNH 22555 (a possible anhanguerid), and in a specific species of Pteranodon: P. longiceps. Analyzing dorsal vertebrae, Buchmann and Rodrigues found that the presence of pneumatic foramina has appeared at least four times independently within these bones, and only in specific types of pterosaurs: the anhanguerids, the azhdarchids, a specific species of Rhamphorhynchus: R. muensteri, and in P. longiceps. They also found that P. longiceps had lateral pneumatic foramina in the mid-cervicals, but none in the posterior cervicals.^[61]