2018-10-11 10:46:01
About 85 million years ago, at the end of the Cretaceous, North America was bisected by a warm, shallow inland sea that crossed the continent from north to south, from the Arctic to the Caribbean. It was the Niobrara Sea. On its coasts lived birds and pterosaurs that fed on the fish that proliferated in its waters. One of the most abundant pterosaurs in the region, and also one of the largest, was Pteranodon, whose fossils have been found in the states of Kansas, Alabama, Nebraska, Wyoming, and South Dakota. It seems that in the northernmost part of the Niobrara Sea, in present-day Canada, there were no pterosaurs. Some fragmentary remains have been discovered on the east coast of the United States, in the Gulf of Mexico, and in Japan, but their membership in the genus Pteranodon is unclear.
Pteranodon was the first pterodactyl to be discovered outside of Europe. Since its discovery by Othniel Charles Marsh in 1870, more than a thousand specimens have been found, which are distributed by museums around the world, and which have allowed us to know its anatomy and development in detail. A dozen species have been described over the years. However, although a definitive consensus has not yet been reached, all the fossils can be assigned to only two species: Pteranodon sternbergi, the oldest, which some authors call Geosternbergia sternbergi, and which lived between 88 and 85 million years ago, and its descendant Pteranodon longiceps, which existed between 86 and 84.5 million years ago.
Most of the differences observed between the various individuals can be explained by sexual dimorphism. Males are distinguished from females by their size, which is 50% larger, by the larger crest that adorns their heads, and by the narrower shape of their pelvis. The pelvis of the females is wider in absolute terms than that of the males, despite the fact that they are much larger; this makes it easier for them to lay eggs. In addition, their crests, like those of the young of both sexes, are smaller and more rounded. As for the differences between the two species, it is simple: the crest of adult male Pteranodon sternbergi is more upright and protruding, while that of Pteranodon longiceps is narrower and projects backwards. Among adults there were variations in the size of the crest, with some males having a long, low second crest on the tip of the bill. So many differences in the shape and size of the crest suggest that it had no use other than to serve as a lure to attract the other sex or in ritualized combat between males.
It has been proposed that the crest could also serve as a counterweight to the bill, but wind tunnel experiments indicate that this only worked for males of the longiceps species. The females’ crest was too small to have any appreciable effect and, worse still, the massive sternbergi male’s crest had the opposite effect; it was so heavy that it required more neck musculature to balance the head than if they had no crest.
Unlike other older pterosaurs, Pteranodon has no teeth. Hence its name, which means “toothless wing”. Its long, narrow, and pointed beak is made of bone. The upper jaw is longer than the lower, and curves upwards. The bill of the males measures more than a meter in length.
The average wingspan of an adult female is just under four meters, while that of males exceeds five and a half meters, and specimens are known to exceed six and even seven meters. The tail is very short; it does not exceed 25 centimeters in the largest males.
The ratio of the wingspan to the width of the wings, which in Pteranodon is nine to one, suggests that its flight was similar to that of the albatross, which has a ratio of eight to one. The flight of albatrosses, which spend a lot of time fishing in the sea, is known as “dynamic glide”, and takes advantage of the vertical gradient of wind speed over the ocean surface to travel long distances without flapping. Pteranodon may have employed a similar strategy, although mechanical studies indicate that the strength of its wings, relative to its weight, allowed it to fly actively as well.
Like other pterosaurs, Pteranodon was quadrupedal when on land, taking off in a leap, with most of the force exerted by the front legs before a rapid flapping of the wings to clear the ground.
Fossils indicate that females outnumbered males; only one in three specimens discovered is a male. The same occurs today in animals with marked sexual dimorphism, in which the male is much larger than the female, as is the case with elephant seals. Like them, Pteranodon may have practiced polygyny, with a few males competing for a large group of females. In that case, the females would dedicate themselves to incubation and rearing, while the only occupation of the males, apart from eating, would be to defend their harem from the other males.
Most of the Pteranodon fossils have been found in places that were hundreds of kilometers out to sea at the time. It is likely that they nested on rocky islands, protected from terrestrial predators, and foraged far offshore. Pteranodon feeds mainly on fish. Floating in the water, a small female would be able to reach depths of up to eighty centimeters with her beak. However, a pterodactyl with a head as large as Pteranodon could not rest floating on the water like an aquatic bird; your center of gravity is too far forward, so your head would tend to sag. You should be constantly moving to keep your head above water and to breathe. On the other hand, the head, neck, and shoulders of Pteranodon are as robust as those of diving birds; it is possible that, like modern gannets, Pteranodon plunged into the water from the sky with its wings drawn back. This underwater fishing technique was not without its dangers in the Niobrara Sea, where sharks and other predatory fish abounded, as well as carnivorous marine reptiles such as mosasaurs and plesiosaurs; in fact, inside the fossils of some of these pterosaur bones have been found.
Pteranodon is one of the most popular pterosaurs; with his trademark crest appearing in many films, from Arthur Conan Doyle’s 1925 version of “The Lost World” and 1933’s “King Kong” to Disney’s “Dinosaur” in 2000 and the “Park” franchise. Jurassic”, going through the sequence of “The Rite of Spring” from “Fantasy”, in 1940, and “A Million Years Ago”, in 1966. There is almost no dinosaur movie in which this great pterosaur does not appear.
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