Genus of pteranodontid pterosaur from the Late Cretaceous
Pteranodon
(
); from
Ancient Greek
πτερ?ν
(
pteron
'wing') and
?ν?δων
(
anodous
,
anodontos
'toothless')
[1]
is a
genus
of
pterosaur
that included some of the largest known flying
reptiles
, with
P. longiceps
having a wingspan of over 6 m (20 ft). They lived during the late
Cretaceous
geological period of
North America
in present-day
Kansas
,
Nebraska
,
Wyoming
,
South Dakota
and
Alabama
.
[2]
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
.
[3]
Pteranodon
is the most famous pterosaur, frequently featured in dinosaur media and strongly associated with dinosaurs by the general public.
[4]
While not dinosaurs, pterosaurs such as
Pteranodon
form a
clade
closely related to dinosaurs as both fall within the clade
Avemetatarsalia
.
Discovery and history
[
edit
]
First fossils
[
edit
]
Pteranodon
was the first pterosaur found outside of
Europe
. Its fossils first were found by
Othniel Charles Marsh
in 1871,
[5]
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).
[6]
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').
[6]
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.
[6]
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.
[7]
Re-evaluation by later scientists has supported Marsh's case, refuting Cope's assertion that
P. umbrosus
represented a larger, distinct species.
[6]
A toothless pterosaur
[
edit
]
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.
[3]
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
.
[8]
[6]
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.
[9]
[6]
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
.
[6]
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.
[10]
Revising species
[
edit
]
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.
[6]
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
.
[6]
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 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 categories or "subgenera" for them.
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 already in use ("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
Occidentalia
(with a small crest), which in turn gave rise to
Pteranodon
with its long backwards crest, finally leading to
Geosternbergia
with its large, upright crest. 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, though Wellnhofer (1978) followed Miller's species list. and Schoch (1984) somewhat oddly published another revision that essentially returned to Marsh's original classification scheme, most notably sinking
P. longiceps
as a synonym of
P. ingens
.
[6]
Recognizing variation
[
edit
]
During the early 1990s, S. Christopher Bennett also published several major papers reviewing the anatomy, taxonomy and life history of
Pteranodon
.
[11]
Fragmentary fossils assigned to
Pteranodon
have also been discovered in
Skane
,
Sweden
.
[12]
Description
[
edit
]
Pteranodon
species are extremely well represented in the fossil record, allowing for detailed descriptions of their anatomy and analysis of their life history. Over 1,000 specimens have been identified, though less than half are complete enough to give researchers good anatomical information. Still, this is more fossils material than is known for any other pterosaur, and it includes both male and female specimens of various age groups and possibly species.
[4]
Adult
Pteranodon
specimens from the two major species can be divided into two distinct size classes. The smaller class of specimens have small, rounded head crests and very wide pelvic canals, even wider than those of the much larger size class. The size of the pelvic canal probably allowed the laying of eggs, indicating that these smaller adults are females. The larger size class, representing male individuals, have narrow hips and very large crests, which were probably for display.
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 5.6 m (18 ft). Adult females were much smaller, averaging 3.8 m (12 ft) in wingspan.
[4]
A large specimen of
Pteranodon longiceps
, USNM 50130, is estimated to have a wingspan of 6.25?6.5 m (20.5?21.3 ft), body length of 2.6 m (8.5 ft) and body mass of 50 kg (110 lb).
[4]
[13]
[14]
[15]
Even larger specimens had wingspans of 7.25?7.6 m (23.8?24.9 ft).
[4]
[16]
While most specimens are found crushed, enough fossils exist to put together a detailed description of the animal.
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, researchers Mark Witton and Mike Habib argued that the largest estimate of 93 kg is much too high and an upper limit of 20 to 35 kg is more realistic. Witton and Habib considered the methods used by researchers who obtained smaller mass estimates equally flawed. Most have been produced by scaling modern animals such as bats and birds up to
Pteranodon
size, despite the fact that pterosaurs have vastly different body proportions and soft tissue anatomy from any living animal.
[17]
Other distinguishing characteristics that set
Pteranodon
apart from other pterosaurs include narrow
neural spines
on the vertebrae, plate-like bony ligaments strengthening the vertebrae above the hip, and a relatively short tail in which the last few vertebrae are fused into a long rod.
[18]
The entire length of the tail was about 3.5% as long as the wingspan, or up to 25 centimeters (9.8 in) in the largest males.
[18]
Skull and beak
[
edit
]
Unlike earlier pterosaurs, such as
Rhamphorhynchus
and
Pterodactylus
,
Pteranodon
had toothless
beaks
, similar to those of
birds
.
Pteranodon
beaks were made of solid, bony margins that projected from the base of the jaws. The beaks were long, slender, and ended in thin, sharp points. The upper jaw, which was longer than the lower jaw, was curved upward; while this normally has been attributed only to the upward-curving beak, one specimen (UALVP 24238) has a curvature corresponding with the beak widening towards the tip. While the tip of the beak is not known in this specimen, the level of curvature suggests it would have been extremely long. The unique form of the beak in this specimen led
Alexander Kellner
to assign it to a distinct genus,
Dawndraco
, in 2010.
[11]
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 (and nowadays placed in its own genus
Geosternbergia
), had a more vertical crest with a broad forward projection, while their descendants,
Pteranodon longiceps
, evolved a narrower, more backward-projecting crest.
[3]
Females of both species were smaller and bore small, rounded crests.
[6]
The crests were probably mainly display structures, though they may have had other functions as well.
[19]
Paleobiology
[
edit
]
Flight
[
edit
]
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).
[20]
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.
[17]
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
.
[21]
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.
[17]
Terrestrial locomotion
[
edit
]
Historically, the terrestrial locomotion of
Pteranodon
, especially whether it was
bipedal
or
quadrupedal
, has been the subject of debate. Today, most pterosaur researchers agree that pterosaurs were quadrupedal, thanks largely to the discovery of pterosaur
trackways
.
[22]
The possibility of aquatic locomotion via swimming has been discussed briefly in several papers (Bennett 2001, 1994, and Bramwell & Whitfield 1974).
Diet
[
edit
]
The diet of
Pteranodon
is known to have included
fish
; fossilized fish bones have been found in the
stomach
area of one
Pteranodon
, and a fossilized fish
bolus
has been found between the jaws of another
Pteranodon
, specimen AMNH 5098. Numerous other specimens also preserve fragments of fish scales and vertebrae near the torso, indicating that
fish made up a majority of the diet
of
Pteranodon
(though they may also have taken invertebrates).
[4]
Traditionally, most researchers have suggested that
Pteranodon
would have taken fish by dipping their beaks into the water while in low, soaring flight. However, this was probably based on the assumption that the animals could not take off from the water surface.
[4]
It is more likely that
Pteranodon
could take off from the water, and would have dipped for fish while swimming rather than while flying. Even a small, female
Pteranodon
could have reached a depth of at least 80 centimeters (31 in) with its long bill and neck while floating on the surface, and they may have reached even greater depths by plunge-diving into the water from the air like some modern long-winged seabirds.
[4]
In 1994, Bennett noted that the head, neck, and shoulders of
Pteranodon
were as heavily built as diving birds, and suggested that they could dive by folding back their wings like the modern
gannet
.
[4]
Crest function
[
edit
]
Pteranodon
was notable for its skull crest, though the function of this crest has been a subject of debate. Most explanations have focused on the blade-like, backward pointed crest of male
P. longiceps
, however, and ignored the wide range of variation across age and sex. The fact that the crests vary so much rules out most practical functions other than for use in mating displays.
[23]
Therefore, display was probably the main function of the crest, and any other functions were secondary.
[19]
Scientific interpretations of the crest's function began in 1910, when George Francis Eaton proposed two possibilities: an aerodynamic counterbalance and a muscle attachment point. He suggested that the crest might have anchored large, long jaw muscles, but admitted that this function alone could not explain the large size of some crests.
[24]
Bennett (1992) agreed with Eaton's own assessment that the crest was too large and variable to have been a muscle attachment site.
[19]
Eaton had suggested that a secondary function of the crest might have been as a counterbalance against the long beak, reducing the need for heavy neck muscles to control the orientation of the head.
[24]
Wind tunnel tests showed that the crest did function as an effective counterbalance to a degree, but Bennett noted that, again, the hypothesis focuses only on the long crests of male
P. longiceps
, not on the larger crests of
P. sternbergi
and very small crests that existed among the females. Bennett found that the crests of females had no counterbalancing effect, and that the crests of male
P. sternbergi
would, by themselves, have a negative effect on the balance of the head. In fact, side to side movement of the crests would have required more, not less, neck musculature to control balance.
[19]
In 1943, Dominik von Kripp suggested that the crest may have served as a
rudder
, an idea embraced by several later researchers.
[19]
[25]
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.
[26]
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.
[27]
Additionally, the rudder and air brake hypotheses do not explain why such large variation exists in crest size even among adults.
[19]
Alexander Kellner
suggested that the large crests of the pterosaur
Tapejara
, as well as other species, might be used for heat exchange, allowing these pterosaurs to absorb or shed heat and regulate body temperature, which also would account for the correlation between crest size and body size. There is no evidence of extra blood vessels in the crest for this purpose, however, and the large, membranous wings filled with blood vessels would have served that purpose much more effectively.
[19]
With these hypotheses ruled out, the best-supported hypothesis for crest function seems to be as a sexual display. This is consistent with the size variation seen in fossil specimens, where females and juveniles have small crests and males large, elaborate, variable crests.
[19]
Sexual variation
[
edit
]
Adult
Pteranodon
specimens may be divided into two distinct size classes, small and large, with the large size class being about one and a half times larger than the small class, and the small class being twice as common as the large class. Both size classes lived alongside each other, and while researchers had previously suggested that they represent different species, Christopher Bennett showed that the differences between them are consistent with the concept that they represent females and males, and that
Pteranodon
species were
sexually dimorphic
. Skulls from the larger size class preserve large, upward and backward pointing crests, while the crests of the smaller size class are small and triangular. Some larger skulls also show evidence of a second crest that extended long and low, toward the tip of the beak, which is not seen in smaller specimens.
[19]
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.
[19]
Note that the overall size and crest size also corresponds to age. Immature specimens are known from both females and males, and immature males often have small crests similar to adult females. Therefore, it seems that the large crests only developed in males when they reached their large, adult size, making the sex of immature specimens difficult to establish from partial remains.
[13]
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.
[19]
Paleoecology
[
edit
]
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.
[6]
Some very fragmentary fossils belonging to pteranodontian pterosaurs, and possibly
Pteranodon
itself, have also been found on the
Gulf Coast
and
East Coast of the United States
. For example, some bone fragments from the
Mooreville Formation
of
Alabama
and the
Merchantville Formation
of
Delaware
may have come from
Pteranodon
, though they are too incomplete to make a definite identification.
[6]
Some remains from Japan have also been tentatively attributed to
Pteranodon
, but their distance from its known Western Interior Seaway habitat makes this identification unlikely.
[6]
Pteranodon longiceps
would have shared the sky with the giant-crested pterosaur
Nyctosaurus
. Compared to
P. longiceps
, which was a very common species,
Nyctosaurus
was rare, making up only 3% of pterosaur fossils from the formation. Also less common was the early toothed
bird
,
Ichthyornis
.
[28]
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.
[19]
Below the surface, the sea was populated primarily by invertebrates such as
ammonites
and
squid
. Vertebrate life, apart from basal fish, included
sea turtles
, such as
Toxochelys
, the
plesiosaurs
Elasmosaurus
and
Styxosaurus
, and the flightless diving bird
Parahesperornis
.
Mosasaurs
were the most common marine reptiles, with genera including
Clidastes
,
Mosasaurus
and
Tylosaurus
.
[3]
At least some of these marine reptiles are known to have fed on
Pteranodon
.
Barnum Brown
, in 1904, reported plesiosaur stomach contents containing "pterodactyl" bones, most likely from
Pteranodon
.
[29]
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
).
[30]
Classification
[
edit
]
Timespan and evolution
[
edit
]
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.
[6]
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.
[28]
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
.
[4]
Valid species
[
edit
]
Many researchers consider there to be at least two species of
Pteranodon
. However, aside from the differences between males and females described above, the post-cranial skeletons of
Pteranodon
show little to no variation between species or specimens, and the bodies and wings of all pteranodonts were essentially identical.
[6]
Two species of
Pteranodon
are traditionally recognized as valid:
Pteranodon longiceps
, the
type species
, and
Pteranodon sternbergi
. The species differ only in the shape of the crest in adult males (described above), and possibly in the angle of certain skull bones.
[6]
Because well-preserved
Pteranodon
skull fossils are extremely rare, researchers use stratigraphy (i.e. which rock layer of the geologic formation a fossil is found in) to determine species identity in most cases.
Pteranodon sternbergi
is the only known species of
Pteranodon
with an upright crest. The lower jaw of
P. sternbergi
was 1.25 meters (4.1 ft) long.
[31]
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.
[6]
Because fossils identifiable as
P. sternbergi
are found exclusively in the lower layers of the Niobrara Formation, and
P. longiceps
fossils exclusively in the upper layers, a fossil lacking the skull can be identified based on its position in the geologic column (though for many early fossil finds, precise data about its location was not recorded, rendering many fossils unidentifiable).
[11]
Below is a
cladogram
showing the phylogenetic placement of this genus within Pteranodontia from Andres and Myers (2013).
[32]
Alternative classifications
[
edit
]
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.
[11]
Disused species
[
edit
]
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 7 meters (23 ft).
[33]
Other valid species include the possibly larger
P. sternbergi
, with a wingspan originally estimated at 9 m (30 ft).
[33]
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
[
edit
]
Status of names listed below follow a survey by Bennett, 1994 unless otherwise noted.
[6]
Name
|
Author
|
Year
|
Status
|
Notes
|
Pterodactylus
oweni
|
Marsh
|
1871
|
Nomen dubium
|
Renamed
Pterodactylus occidentalis
Marsh 1872 on grounds of
oweni
being preoccupied by "Pterodactylus oweni" Seeley 1864 (
nomen nudum
for
Ornithocheirus oweni
Seeley 1870)
|
Pterodactylus
ingens
|
Marsh
|
1872
|
Reclassified as
Pteranodon ingens
|
|
Pterodactylus
occidentalis
|
Marsh
|
1872
|
Junior objective synonym of
Pterodactylus oweni
|
Reclassified from
Pterodactylus oweni
Marsh 1871 on grounds of
P. oweni
being preoccupied by "Pterodactylus oweni" Seeley 1864 (
nomen nudum
for
Ornithocheirus oweni
Seeley 1870)
|
Pterodactylus
velox
|
Marsh
|
1872
|
Nomen dubium
|
Reclassified as
Pteranodon velox
|
Ornithochirus umbrosus
|
Cope
|
1872
|
Nomen dubium
|
|
Ornithochirus harpyia
|
Cope
|
1872
|
Nomen dubium
|
|
Pterodactylus umbrosus
|
(Cope) Cope
|
(
1872
)
1874
|
Reclassification of
Ornithochirus umbrosus
|
|
Pteranodon longiceps
|
Marsh
|
1876
|
Valid
|
Type species
|
Pteranodon ingens
|
(Marsh) Williston
|
(
1872
)
1876
|
Nomen dubium
|
Reclassified from
Pterodactylus ingens
|
Pteranodon occidentalis
|
Marsh
|
(
1872
)
1876
|
Junior objective synonym of
Pterodactylus oweni
|
Reclassified from
Pterodactylus occidentalis
|
Pteranodon velox
|
Marsh
|
(
1872
)
1876
|
Nomen dubium
|
Reclassified from
Pterodactylus velox
, based on a juvenile specimen
|
Pteranodon gracilis
|
Marsh
|
1876
|
Reclassified as
Nyctosaurus gracilis
|
|
Pteranodon comptus
|
Marsh
|
1876
|
Nomen dubium
|
|
Pteranodon nanus
|
Marsh
|
1876
|
Reclassified as
Nyctosaurus nanus
|
|
Ornithocheirus
umbrosus
|
(Cope) Newton
|
(
1872
)
1888
|
Reclassified as
Pteranodon umbrosus
|
Spelling correction of
Ornithochirus umbrosus
|
Ornithocheirus
harpyia
|
(Cope) Newton
|
(
1872
)
1888
|
Reclassified as
Pteranodon harpyia
|
Spelling correction of
Ornithochirus harpyia
|
Pteranodon umbrosus
|
(Cope) Williston
|
(
1872
)
1892
|
Nomen dubium
|
Reclassification of
Ornithochirus umbrosus
|
Ornithostoma
ingens
|
(Marsh) Williston
|
(
1872
)
1893
|
Synonym of
Pteranodon ingens
|
Reclassified from
Pteranodon ingens
|
Ornithostoma
umbrosum
|
(Cope) Williston
|
(
1872
)
1897
|
Synonym of
Pteranodon umbrosus
|
Reclassified from
Pteranodon umbrosus
|
Pteranodon oregonensis
|
Gilmore
|
1928
|
Reclassified as
Bennettazhia oregonensis
|
|
Pteranodon sternbergi
|
Harksen
|
1966
|
Valid
|
|
Pteranodon marshi
|
Miller
|
1972
|
Synonym of
Pteranodon longiceps
|
|
Pteranodon bonneri
|
Miller
|
1972
|
Reclassified as
Nyctosaurus bonneri
|
|
Pteranodon walkeri
|
Miller
|
1972
|
Synonym of
Pteranodon longiceps
|
|
Pteranodon (Occidentalia) eatoni
|
(Miller) Miller
|
(
1972
)
1972
|
Synonym of
Pteranodon sternbergi
|
|
Pteranodon eatoni
|
(Miller) Miller
|
(
1972
)
1972
|
Synonym of
Pteranodon sternbergi
|
Reclassified from
Pteranodon (Occidentalia) eatoni
|
Pteranodon (Longicepia) longicps
[
sic
]
|
(Marsh) Miller
|
(
1872
)
1972
|
Synonym of
Pteranodon longiceps
|
Reclassified from
Pteranodon longiceps
|
Pteranodon (Longicepia) marshi
|
(Miller) Miller
|
(
1972
)
1972
|
Synonym of
Pteranodon longiceps
|
Reclassified from
Pteranodon marshi
|
Pteranodon (Sternbergia) sternbergi
|
(Harksen) Miller
|
(
1966
)
1972
|
Reclassified as
Pteranodon (Geosternbergia) sternbergi
|
Reclassified from
Pteranodon sternbergi
|
Pteranodon (Sternbergia) walkeri
|
(Miller) Miller
|
(
1972
)
1972
|
Reclassified as
Pteranodon (Geosternbergia) walkeri
|
Reclassified from
Pteranodon walkeri
|
Pteranodon (Pteranodon) marshi
|
(Miller) Miller
|
(
1972
)
1973
|
Synonym of
Pteranodon longiceps
|
Reclassified from
Pteranodon marshi
|
Pteranodon (Occidentalia) occidentalis
|
(Marsh) Olshevsky
|
(
1872
)
1978
|
Synonym of
Pteranodon occidentalis
|
Reclassified from
Pteranodon occidentalis
|
Pteranodon (Longicepia) ingens
|
(Marsh) Olshevsky
|
(
1872
)
1978
|
Synonym of
Pteranodon ingens
|
Reclassified from
Pteranodon ingens
|
Pteranodon (Pteranodon) ingens
|
(Marsh) Olshevsky
|
(
1872
)
1978
|
Synonym of
Pteranodon ingens
|
Reclassified from
Pteranodon ingens
|
Pteranodon (Geosternbergia) walkeri
|
(Miller) Miller
|
(
1972
)
1978
|
Synonym of
Pteranodon longiceps
|
Reclassified from
Pteranodon walkeri
|
Pteranodon (Geosternbergia) sternbergi
|
(Harksen) Miller
|
(
1966
)
1978
|
Synonym of
Pteranodon sternbergi
|
Reclassified from
Pteranodon (Sternbergia) sternbergi
|
Pteranodon orientalis
|
(Bogolubov) Nesov & Yarkov
|
(
1914
)
1989
|
Reclassified as
Bogolubovia orientalis
|
Reclassified from
Ornithostoma orientalis
|
Geosternbergia walkeri
|
(Miller) Olshevsky
|
(
1972
)
1991
|
Synonym of
Pteranodon sternbergi
|
Reclassified from
Pteranodon (Sternbergia) walkeri
|
Geosternbergia sternbergi
|
(Harksen) Olshevsky
|
(
1966
)
1991
|
Synonym of
Pteranodon sternbergi
|
Reclassified from
Pteranodon (Geosternbergia) sternbergi
|
See also
[
edit
]
References
[
edit
]
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Further reading
[
edit
]
- Anonymous. 1872. On two new Ornithosaurians from Kansas.
American Journal of Science
, Series 3, 3(17):374?375. (Probably by O. C. Marsh)
- Bennett, S. C. 2000. New information on the skeletons of
Nyctosaurus
. Journal of Vertebrate Paleontology 20(Supplement to Number 3): 29A. (Abstract)
- Bennett, S. C. (2001). "The osteology and functional morphology of the Late Cretaceous pterosaur
Pteranodon
. Part II. Functional morphology".
Palaeontographica, Abteilung A
.
260
: 113?153.
doi
:
10.1127/pala/260/2001/113
.
S2CID
210463400
.
- Bennett, S. C. (2003). "New crested specimens of the Late Cretaceous pterosaur
Nyctosaurus
".
Palaontologische Zeitschrift
.
77
: 61?75.
doi
:
10.1007/bf03004560
.
S2CID
129438441
.
- Bennett, S. C. (2007).
"Articulation and function of the pteroid bone of pterosaurs"
(PDF)
.
Journal of Vertebrate Paleontology
.
27
(4): 881?891.
doi
:
10.1671/0272-4634(2007)27[881:aafotp]2.0.co;2
.
S2CID
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