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Pterosaurs - A Celebration of the Diversity of Life

Although new fossils and new computer models have completely changed our views of pterosaurs, in pop culture they are still portrayed as leathery, winged, emaciated-looking bat creatures. Even in recent dinosaur movies such as the Jurassic Worlds, they are blood thirsty, leathery, beasts that snatch people from the ground. It’s time to view pterosaurs for what they are, miracles of evolution… a celebration of the diversity of life.

Many types of pterosaurs such as Pteranodon longiceps, spent their lives near or on the seas eating fish. However, many other pterosaurs were uniquely adapted for very different environments; their diversity is staggering. Some, like Nemicolopterus crypticus, were insectivores as small as finches and lived the forests canopies (Wang et al., 2008). Others like Dimorphodon macronyx would scurry around on all fours eating forests insects (Witton, 2015 & Pickrell, 2018). The large Pterodaustro guiñazui were like flamingos and waded in salt marshes filtering small crustaceans and plankton (Qvarnström et al., 2019). Alcione elainus, with its very short and robust wings may have been adapted for plunge diving like modern gannets (Longrich et al., 2018). Others like Quetzalcoatlus northroppi, with a 35 foot wingspan, lived more inland and were like gigantic storks plucking small animals off the ground (Witton and Nash, 2008). If you can find a niche, there was a pterosaur for it!

By the way, if you want to see the cutest pterosaur of all time, check out this scientific illustration of an anurognathid pterosaur. Specimens from this family have been found completely covered with hair and feather-like structures (Yang et al., 2019), making them the cutest and cuddliest furballs of the Late Jurassic. Click here to see the image from the illustrator.

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Unique Flight Mechanics

Similar to birds, pterosaurs were lightweight with a very efficient respiratory system. Their bones were incredibly thin and hollow. Some were as thin as paper but very flexible. Their lungs were also similar to bird lungs in that they had air sacs that were connected to the lungs which provided a constant flow of air while breathing, which is important when flying (Claessens et al., 2009). Even though we can compare the internal structure of their bones and super-efficient lungs to that of modern day birds, the similarities end there. Since they independently evolved flight nearly 70 million years before birds, the flight mechanics are very different.

Pterosaurs were very efficient flyers and their wings are unique in the animal world, far different from birds and bats. They have an incredibly elongated fourth finger digits which forms the wings. The main wing membrane is attached to the end of the fourth digit and runs down to the hind legs. Pterosaurs did not have flight feathers like birds to help create lift; instead, the work was done by the wing membrane. This thin and complex membrane consists of multiple layers of tissue. One layer has blood vessels, one has fibrous cords, and one has muscles (Martill and Unwin, 1989). With these cords and muscles, the wing membrane could change its tension and shape while flying.

The take-off dynamics of pterosaurs are also unique. Unlike birds which are bipedal, numerous trackways indicate pterosaurs were quadrupedal, or walked on all fours with their 4th wing finger folded back. This means they could use their long arms as well as legs to help launch them into the sky, kind of like pole vaulting (Habib, 2008). Although numerous walking traces and a single landing trace (Mazin et al., 2009) have been found, no takeoff traces have been discovered. However, the possible quadruped launch mechanics can allow even the largest pterosaurs to easily achieve flight (Witton and Habib, 2010), and also allows for efficient water launches (Habib 2013).

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Whimsical Proportions

Along with their wings, pterosaur bodies were uniquely shaped. They were very disproportionate compared to living animals today. In the Triassic, many pterosaurs had long tails and teeth and semi-regular sized heads. However, over time, small tailed and toothless forms became much more common, and their heads and necks grew larger and larger. By the Cretaceous, many pterosaur heads grew to almost whimsical proportions, as the head and neck took up 3/4 of the length of the pterosaur body. To keep the large skulls lightweight, they had large holes in them, which were filled with tissue or air sacs. To support the oversized head, the neck vertebra were robust and probably very muscular.

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Our Furry Friends

Back in 1831, the zoologist George August Goldfuss noticed inch long strands covering the body of a well preserved Scaphognathus pterosaur. Since then, other pterosaurs have been found with various types of these structures. It is surmised that at least the bodies of pterosaurs were covered in these hair-like structures that Kellner et al. called pycnofibers (2010). This comes as no surprise because they have the same common ancestor as dinosaurs, many of which have feathers.

Later, in 2018, Yang et al., found four types of complex feather-like structures on two well preserved anurognathid pterosaur specimens. They found the pycnofiber-like structures on their bodies, but also found feather like structures on their wings. They concluded these filaments probably “functioned in thermoregulation, tactile sensing, signaling and aerodynamics (Yang et al., 2018). Based on the numerous specimens, it’s now assumed there was a wide variation in the amount and types of hair and feather-like structures on different groups of pterosaurs.

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Elaborate Head Crests

Adding to the uniqueness of pterosaurs is the amazing diversity of head crests. Many supported bony crests, with some being quite large and bizarre looking. Better preserved fossils suggest many other "crestless" pterosaurs actually had crests made of keratin that did not preserve.

The function of these elaborate head crests have always been speculative until a unique discovery in China. In 2011, the discovery of a small leathery egg inside a Jurasic Darwinopterus pterosaur confirmed that females of this genus did not have head crests (Lu et al., 2011). It appears that males of some pterosaurs only had crests, and in some pterosaur groups, the female head crests were reduced. Based on this information, crests were most likely used for display and mating behavior and therefore were probably very ornamental and colorful.

One notable example of an extreme crest is the Late Cretaceous Nyctosaurus from the Western Interior Seaway. Both sexes of this long winged pterosaur supported a two pronged bony crest. In males, the crest was larger than the entire body. It would have looked like a giant antler. Research on Nyctosaurus suggests there would not have been skin or keratin between the forks of the crest (Bennette 2003).

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Conclusion

Even though pterosaurs died with the dinosaurs and most birds during the end Cretaceous extinction event, with over 150 species discovered, pterosaurs were a very successful group. They diversified into many different ecological niches and ruled the skies for over 150 million years. Pterosaurs even coexisted with birds for tens of millions of years. Since many of their bones are extremely thin and hollow, fossils of pterosaurs are rare. This means the complete picture of pterosaurs is far from complete. It’s likely that even stranger and better preserved specimens will be discovered, which will show just how remarkable these animals were. They are truly a celebration of the diversity of life.

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Recommended Pterosaur Books and Educational Items:

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Works Cited:

Bennett S.C. (2003) New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Paläontologische Zeitschrift, 77: 61-75.

Claessens L.P.A.M., O'Connor P.M., Unwin D.M. (2009) Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism. PLOS ONE 4(2): e4497. https://doi.org/10.1371/journal.pone.0004497.

Habib M.B. (2013) Constraining the air giants: limits on size in flying animals as an example of constraint-based biomechanical theories of form. Biol. Theory 8(3): 245-252

Habib M.B. (2008) Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28: 161–168.

Kellner, A.W.A., Wang, X., Tischlinger, H., de Almeida Campos, D., Hone, D.W.E., and Meng, X. (2010) The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proceedings of the Royal Society B: Biological Sciences, 277:321-329. https://doi.org/10.1098/rspb.2009.0846.

Longrich N.R., Martill D.M., Andres B. (2018) Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary. PLOS Biology 16(4): e1002627. https://doi.org/10.1371/journal.pbio.1002627.

Lü J., Unwin D.M., Deeming D.C., Jin X., Liu Y., Ji Q. (2011) An egg-adult association, gender, and reproduction in pterosaurs. Science. 331 (6015): 321–324. https://doi.org/10.1126/science.1197323.

Martill, D.M., Unwin, D.M. (1989) Exceptionally well-preserved pterosaur wing membrane from the Cretaceous of Brazil. Nature, 340: 138.

Mazin J.M., Billon-Bruyat J.P., and Padian K. (2009) First record of a pterosaur landing trackway 276 Proc. R. Soc. B. https://doi.org/10.1098/rspb.2009.1161.

Pickrell J. (2018) Tooth scratches reveal new clues to pterosaur diets. (2018) Nature. Jan 11;553(7687):138. https://doi.org/10.1038/d41586-018-00080-y.

Qvarnström M., Elgh E., Owocki K., Ahlberg P.E., Niedzwiedzki G. (2019) Filter feeding in Late Jurassic pterosaurs supported by coprolite contents. PeerJ 7:e7375 https://doi.org/10.7717/peerj.7375.

Wang, X., Kellner, A.W., Zhou, Z., & Campos, D. (2008) Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China. Proceedings of the National Academy of Sciences of the United States of America, 105(6), 1983–1987. https://doi.org/10.1073/pnas.0707728105.

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. https://doi.org/10.1371/journal.pone.0013982.

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. https://doi.org/10.1371/journal.pone.0013982.

Witton, M.P.; Naish, D. (2008) A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE. 3 (5): e2271. https://doi.org/10.1371/journal.pone.0002271.

Witton, M.P. (2015) Were early pterosaurs inept terrestrial locomotors? PeerJ 3:e1018; https://doi.org/10.7717/peerj.1018.

Yang Z., Jiang B., McNamara M.E., Kearns S.L., Pittman M., Kaye T.G., Orr P.J., Xu X., Benton M.J. (2019) Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution, 3 (1): 24 https://dx.doi.org/10.1038/s41559-018-0728-7.

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