Pteranodon: Beast of the Week

Today we will be looking at the most iconic pterosaur of all.  Check out Pteranodon longiceps!

Pteranodon was a large pterosaur (prehistoric flying reptile that was not a dinosaur.) that lived in what is now central United States, including Kansas, Alabama, Nebraska, Wyoming, and South Dakota, during the Late Cretaceous Period, between 86 and 84.5 million years ago.  The biggest Pteranodons on record have wingspans of over twenty feet from tip to tip, but average males were more close to eighteen feet and the females (Yes, we are pretty sure we can tell the two sexes.  More on that later.) were a bit smaller, with about a twelve foot wingspan.  When alive Pteranodon would have been a meat-eater, feeding on fish and other marine prey that lived in the shallow sea that once covered the region of the the country that Pteranodon would have flown over in life.  The genus name, Pteranodon, translates to "Toothless Wing" because...wait for it...it didn't have any teeth and it had wings.  Ironically there are way too many pop culture representations of this animal that have teeth!

Two male Pteranodon longiceps fight over a cephalopod.  Reconstruction by me in watercolors.

Pteranodon is a very well-studied animal, known from over one thousand fossil specimens!  Among these individuals we find two body types.  One type is the most iconic vision of this animal, being the larger of the two, with an average wingspan of eighteen feet (but some are larger as stated above) with a long, pointed crest growing out of the back of the skull.  The second body type is much smaller, with only a twelve-foot wingspan. (Still huge if you consider the largest flying animal today, the Wandering Albatross, has a wingspan just under that.) These smaller individuals also had a short, blunt crest behind the head and wide hips, even wider when compared to their in every other way larger crested counterparts.  At first it may seem there were two species of related pterosaurs sharing the same environment, but upon closer inspection, the evidence is pointing to one species that was sexually dimorphic.  (sexual dimorphism- when the males and females of a species look different.) The the larger, crested type was the male, and the smaller, short-crested, was the female.  Why do we think these two forms were different sexes of the same species and not simply two different species?  Let's look at the three key differences between them I listed above.

Skeletal mount of a female (probably) Pteranodon hanging from the gift shop ceiling of the American Museum of Natural History in New York.

1) Size
This isn't actually an indicator of sexual dimorphism by itself.  This is because within reptiles, there are many examples of female-larger and male-larger species across the board.  Sometimes even within the same genus of reptile there are variations with male and female size dimorphism.  So that one is out as far as evidence goes.  Let's look at the other two clues.

2) Crests
In almost all animals that use display structures like colors, frills, horns, manes, or crests as a difference between the sexes, the males are the ones that have more going on. Don't misunderstand me here!  There are plenty of species where both the males AND females have cool structures...it's just in the ones that there is a difference between the two, the males are the ones with the more visually intense bits to show potential mates how healthy they are.  It's more biologically taxing to be the female, carrying and giving birth, so males are often the ones competing for their attention, instead of the other way around.  If these two forms were opposite sexes, the ones with the long crests would more likely be the males.

3) Hips
This is the strongest piece of evidence.  The smaller individuals with short crests had wider hips.  Wider hips are found in females of almost any species of vertebrate for giving birth.  In this case, wider hips would make it easier for those individuals to carry and lay eggs.  The fact that they are specifically wider than those of the other body type that is larger in every other way, including a cool display crest, strongly suggests we are looking at males and females of the same species.

Sketch I did in graphite of a female (probably) Pteranodon longiceps.

Beyond being one of the few fossil species we can pretty confidently distinguish the males from the females in, Pteranodon had a number of other cool things going on with its anatomy.  Let's start with that beak.  It was huge!  In fact, Pteranodon's skull is much longer than the rest of its body!  A beak like that, combined with the evidence that this animal spent much of its life soaring over the sea, would have been excellent for snatching up fish and other small marine prey.  Pteranodon may have even dove for its food, using its beak like a spear to catch prey even deeper under the water's surface.  Having a long beak is a helpful adaptation for a predator hunting prey in the water because it greatly extends the striking range without having to move the whole body much.  To further support the idea it was a fish-eater, fish bone and scale fossils have been found in the stomach cavities of Pteranodon specimens.

Pteranodon mount on display at the American Museum of Natural History in New York.

Pteranodon had particularly long wings, even for a pterosaur, because it was adapted for soaring long distances.  We can see parallels in flying animals, like birds, today.  Birds that live most of their lives soaring over the ocean, like albatross, have long, tapered, wings, as well.  Like them, it is likely Pteranodon was capable of going long distances without flapping.  It may have even been able to sleep while flying!  (although we don't have direct proof of that)  That being said, the arm bones of Pteranodon suggest it had HUGE muscles there in life, so flapping wouldn't have been a problem for this pterosaur, either, if i t needed to do so.

Pteranodon longiceps male (probably) skeleton hanging in the American Museum of Natural History's temporary pterosaurs exhibit.

Since all the Pteranodon fossils on record were unearthed in an area that would have been a sea during the times of their deaths, we can logically assume Pteranodon spent most of its time flying over water, probably resting and nesting on islands or rocky cliffs surrounded by, or near the water.  While Pteranodon, itself, was an adept predator, it had to watch out when it got near or in the water for the gigantic sea monsters it shared its world with.  Most notable was the mosasaur, Tylosaurus.

Lastly, please don't refer to Pteranodon as "pterodactyl".  Too often are pop culture depictions of pterosaurs labelled as "pterodactyl", but are clearly based on Pteranodon.  Seriously, if you say "pterodactyl" that in front of a paleontologist, he or she will no doubt correct you with a pleasant smile, but I promise you that poor scientist is screaming inside.

References

Bennett, S.C. (1992). "Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests". Journal of Vertebrate Paleontology. 12 (4): 422–434. 

Bennett, S.C. (1994). "The Pterosaurs of the Niobrara Chalk". The Earth Scientist. 11 (1): 22–25.

Bennett, S.C. (2000). "Inferring stratigraphic position of fossil vertebrates from the Niobrara Chalk of western Kansas." Current Research in Earth Sciences: Kansas Geological Survey Bulletin, 244(Part 1): 26 pp.

Tomkins, J. L.; Lebas, N. R.; Witton, M. P.; Martill, D. M.; Humphries, S. (2010). "Positive Allometry and the Prehistory of Sexual Selection". The American Naturalist. 176 (2): 141–148.

Witton, M.P.; Habib, M.B. (2010). "On the Size and Flight Diversity of Giant Pterosaurs, the Use of Birds as Pterosaur Analogues and Comments on Pterosaur Flightlessness". PLoS ONE. 5 (11): e13982.