Thursday, 2 January 2020

The weirdest things people have thought about pterosaurs

Fig. 1: When people think of pterosaurs, they usually imagine a skeletal gargoyle, like in this Burian-painting, that could be right at home in a gothic castle.
"If dinosaurs are badly portrayed in movies, then pterosaurs have an even worse time!" is a quote that TV Tropes attributes to Dougal Dixon. Unfortunately, they do not provide a source, so I cannot confirm if he actually said that. If he did it would be highly ironic, as Dixon is known for his… less than ideal portrayal of pterosaurs in some of his books, such as The New Dinosaurs. Regardless of attribution or irony, the quote does hold a lot of truth. The portrayal of dinosaurs, while slow, has changed and is changing a lot in popular media. No longer are they cold-blooded, tail-dragging behemoths, but instead agile, bird-like creatures. There are even rumours about feathered dinosaurs finally appearing in the third Jurassic World movie (which is about damn time). Their close relatives, pterosaurs, on the other hand always seem to get the shaft. While actual science has greatly progressed on our view of pterosaurs, pop-culture has often not even attempted to do the same. The Pteranodons that appear in 2015’s Jurassic World barely evolved and still look like their 1930s counterparts would: Naked skin, leathery wings, bloodthirsty and able to grab people by their shoulders and carry them through the air. Arguably more than dinosaurs, pterosaurs are often viewed as fantastic, otherworldly creatures, more similar to gargoyles than to animals. In some ways they certainly were weird and if they survived into historic times I would argue we would have probably classified them as their own vertebrate class. On the other hand, a lot of this may be attributed to bizarre ideas people have had about them in the past and present, which were often popularized but had little connection to reality. In this post I want to present just some of these, mostly out of pure fun and curiosity.

Pterosaurs as flying marsupials

The fact that pterosaurs were reptiles was recognized as early as 1801 by French anatomist Georges Cuvier, father of vertebrate paleontology, in his description of the then newly discovered Pterodactylus. However, this did not stop others from giving their own interpretation of the bizarre-looking fossil from Bavaria. In a lecture form 1810, Samuel Thomas von Soemerring presented his conclusion that the fossil, which he called Ornithocephalus, was in fact a mammal very similar to bats or flying foxes and should be classified as intermediate between Mammalia and Aves. In his view, bats gave rise to birds and pterosaurs were the transitional form between them. His conclusion was largely based on a misinterpretation of the forelimb-bones and ignoring many of the reptilian characteristics of the skeleton, such as the jaw-joints. While Soemerring’s interpretation was dominant among German scientists for a while, it ultimately lost to Cuvier’s, thanks to his authority and good counter-arguments. It did however not vanish before giving rise to an even more bizarre idea: In 1843 English zoologist Edward Newman interpreted pterosaurs not just as mammals, but as flying marsupials more specifically. He even illustrated them with cute ears, fur and pouches.
Fig. 2: Pterosaurs as imagined by Edward Newman. Peter Wellnhofer seems to find the ears particularly endearing (Wellnhofer 1991, p. 28).
What I always found interesting about the mammalian classification of pterosaurs, from a “what if” perspective, is that in life they did in fact possess a very hair-like body-covering called pycnofibers (although recent studies suggest they may have been more similar in structure to primitive feathers). As early as 1831 Georg August Goldfuss actually discovered these pycnofibers in a fossil, but his claims were largely dismissed and ignored. They were instead reconstructed with smooth skin or scales for the longest time. That pterosaurs did in fact have pycnofibers was only conclusively proven in 1971 with the discovery of Sordes pilosus. Now the fun part is to imagine what would have happened if Goldfuss was actually taken seriously back in the day or if pycnofibers were discovered even earlier. It is not hard to imagine that these filaments would have initially been interpreted as true fur and that this would have given more fuel to the mammalian classification. Who knows how long it may have outstayed its welcome? It should nonetheless be mentioned that, despite finding pycnofibers, Goldfuss himself still classified pterosaurs as reptiles.
Fig. 3: An 1857 painting by Adolphe François Pannemaker, where we can again see a bat-like interpretation of pterosaurs.
While we are on the topic of alternate realities, Edward Newman’s idea of flying marsupials in general is a worthwhile discussion for fans of speculative evolution. It has been argued that marsupials generally cannot specialize their forelimbs to the degree other mammals can, as in the fetal state their offspring require grasping hands to climb from the vulva up the mother’s belly into the pouch. We do however know marsupials with strongly derived forelimbs, such as the now extinct pig-footed bandicoot Chaeropus, which possessed hooves on its hands. Then there are of course sugar gliders, which are basically the possum-version of a flying squirrel. There are also some groups that completely circumvent the usual reproduction by pouch, such as marsupial mice. Perhaps one day we may find a fossil marsupial capable of powered flight.

Pterosaurs as marine monotremes

Even more bizarre than the classification of pterosaurs as flying mammals is the interpretation given to us by Johann Georg Wagler in 1830. When Pterodactylus was first described in 1784 by Cosimo Alessandro Collini, he interpreted the forelimbs as membranous paddles and thought it was an aquatic creature. Wagler stuck with Collini’s conclusion and grouped pterosaurs together with ichthyosaurs and plesiosaurs in a new vertebrate-class which he called Gryphi, literally Latin for griffins. Within Gryphi he also grouped the extant monotremes, the egg-laying mammals platypus and echidna. Similar to Soemerring he viewed Gryphi as transitional between birds and mammals, although if I interpreted his writing correctly he also saw them as directly ancestral to cetaceans. He especially liked comparing the head of Pterodactylus to that of a dolphin (Wagler 1830, p.64). I must admit, even though I am able to read the original German text, I am just as confused as you are. I guess he imagined that sea-birds evolved into aquatic pterosaurs, which then evolved into ichthyosaurs and monotremes. Out of the ichthyosaurs the whales arose, while mammals derived from monotremes. Or the other way around?

Fig. 4: Pterodactylus as reconstructed by Johann Georg Wagler. The feet and wings were imagined as paddles purely used to swim in a penguin-like fashion. The reconstruction of the skull seems to be based more on a dolphin than on the actual fossil.

Pterosaurs as the missing bird-dinosaur link

Closer to the mark than the previous two was English geologist Harry Govier Seeley when in 1901 he published Dragons of the Air. His book was actually the only major work focused entirely on pterosaurs until 1990(!) when Peter Wellnhofer published his Illustrated Encyclopedia of Pterosaurs. Seeley called them Saurornia or Ornithosauria and saw them as the transitional form between dinosaurs and birds. He also argued that they were warm-blooded, which brought him into conflict with Richard Owen, who wanted to see them as inferior, cold-blooded reptiles. He was also one of the first to draw pterosaurs in a quadrupedal posture with erect limbs.
Fig. 5: The archosaur family-tree as imagined by Robert Bakker in 1986. He includes pterosaurs among Dinosauria, based on their ankles. He also grouped Ornithischia and Sauropodomorpha together in Phytodinosauria. While both views have largely fallen out of favour, they are still being discussed today from time to time. I apologize for crudely having to photograph the page, as my scanner has trouble handling books of this format without breaking their spine.
Today we know that birds directly descend from small theropod dinosaurs (in fact they still are dinosaurs) and that pterosaurs are not dinosaurs, even though the public sometimes treats them like “honorary dinos”. They nonetheless still are one of the closest sister-clades to dinosaurs, together comprising the larger archosaur-group Avemetarsalia/Ornithodira. Some, like Robert T. Bakker, have argued that pterosaurs should be included in the definition of dinosaurs, essentially making Ornithodira and Dinosauria synonymous. I honestly would not strictly oppose such a decision, although I believe it would go against a lot of current nomenclature laws. Anyway, if you want to be really technical, since birds are the closest living relatives of pterosaurs, you could get away with calling the latter stem-birds.

Pterosaurs could not fly

What is not an idea of outdated Victorian era science is the notion that some or all pterosaurs were not capable of powered flight, as even today one can still find people online who think they were just reptilian hang-gliders. As pterosaurs are extinct and a lot more ancient than birds or bats, prejudice demands that their style of flight must have been inferior to that of their successors. It was therefore often thought that they were not capable of actively flapping their wings and could not become airborne without help. Their number one method of taking off was imagined to be throwing themselves off sea-side cliffs and riding thermal winds. A variation of this is the idea that some pterosaurs, like Pteranodon or Quetzalcoatlus were so large that they simply could not get off the ground, an idea still alive in modern pseudoscience and on Reddit. The fact that the anatomy of these giant pterosaurs was still obviously adapted to flight (I mean, have you seen those wings?) and has no similarities to that of flightless birds is either ignored or taken as a sign that they were capable of flight, but only because atmospheric conditions or even Earth’s gravity were different in the past.
Fig. 6: Secondarily flightless pterosaurs are a popular motif in speculative evolutionary scenarios. The idea was largely popularized by Dougal Dixon’s The New Dinosaurs, where, in a world that never saw the End-Cretaceous extinction event, the lank roams the savannahs of Africa instead of giraffes. The idea may have unintentionally inspired modern proposals that azhdarchids were flightless.
All of that is of course nonsense. Pterosaurs were active, muscular animals with bird-style hollow-bones and air sacs, perfectly capable of powered and prolonged flight. Some sea-goers like Pteranodon may have relied more on gliding on thermal currents, but in the same way as an albatross or a pelican would, not a hang-glider. They certainly did not require cliffs or trees to become airborne. A big reason that lead to the assumption that giant pterosaurs could not lift off on their own was the idea that they were bipedal and would have taken off the same way birds did. We now know that they were quadrupeds and that their method of lift-off most likely closely resembled that of bats, which pole-vault themselves into the air with their powerful arms. This allows the membranes to immediately catch the wind. This is in fact a more efficient way of taking off than that of birds, some bats are even capable of taking into the air in a vertical direction like a helicopter. The combination of bat-style take-off with bird-style hollow bones and air sacs made it perfectly possible for a giant like Quetzalcoatlus to take off on its own, no cliff or alien atmosphere required. While such a creature may have existed, to this date there is no known pterosaur that actual paleontologists regard as flightless.

Pterosaurs could not walk

As if to further ridicule them, some researchers did not even grant pterosaurs the ability to walk on the ground. In 1974, basing their conclusion on earlier ideas, C. D. Bramwell and G. R. Whitfield argued that pterosaurs such as Pteranodon were not able to stand and instead helplessly flopped around on their bellies, shoving themselves forward with their hindlegs. The idea is perhaps comparable to how penguins sometimes slide across ice. Like mentioned earlier, they thought it could only become airborne by suicidally sliding itself off cliffs. This was just one of the weird ideas about pterosaur gait. Popular around the 80s was Kevin Padian’s notion that small pterosaurs like Dimorphodon walked bipedally and digitigrade, as if to mimic theropods. Chris Bennett expanded on this and hypothesized that big, short-tailed pterosaurs actually stood in an upright posture, in a disturbingly human fashion (or if you will like Rodan in the old Godzilla movies). These ideas soon became outdated in the 90s and 2000s as pterosaur-trace-fossils, namely Pteraichnus, were re-evaluated and it was realized that pterosaurs were plantigrade quadrupeds with erect legs and a gait similar to long-limbed mammals.
Fig. 7: Outdated ideas about pterosaur-locomotion as illustrated by Mark Witton. A is a Dimorphodon with a dinosaur-like gait as imagined by Kevin Padian. B is the utterly useless “Penguinodon” as imagined by Bramwell and Whitfield. C is Bennett’s Rodan-wannabe. D is the quadrupedal, bat-like posture as imagined by Wellnhofer. Based on what we know now, Wellnhofer got the closest, but today pterosaurs are imagined to have had an erect, non-sprawling leg-posture.

Live-bearing, bipedal Pteranodon

2005’s Oceans of Kansas by Michael J. Everhart is a great book that I recommend to anyone even remotely interested in the Western Interior Seaway. That said, there were a few bits while reading it that seemed odd. What particularly stood out to me was the chapter about pterosaurs, in which the author supports or speculates about outdated ideas while seemingly dismissing more modern evidence. I want to stress here that I read the second, updated edition from 2017. For one he still uses Padian’s 1983 paper to suggest Pteranodon was a biped and dismisses the Pteraichnus trackways as inconclusive, contrary to the consensus (Everhart 2005, p. 300 – 301). Even more egregious is how he acknowledges the discovery of Chinese pterosaur eggs in 2010, then dismisses them as only pertaining to small pterosaur species. Based on that he then goes as far as speculating that Pteranodon may have given live birth and cared for their young in pairs similar to frigate birds (Everhart 2005, p. 297). While of course this is just speculation on the author’s part, it is still weird to come to such ideas, given the evidence. The argumentation is essentially founded on saying that since we do not have direct evidence for Pteranodon specifically being an oviparous quadruped, this gives us a free-pass to wildly speculate. We have pretty conclusive evidence that all pterosaurs were quadrupeds and there is nothing that would suggest some of them were viviparous. It is also doubtful if they even cared for their young. While in popular media pterosaurs are often depicted as taking care of their young similar to birds, fossil evidence of buried eggs and fully developed hatchlings suggest otherwise. It is generally thought that pterosaurs reproduced in a way that I liken to “flying sea-turtles”. They dug a hole in the ground, laid their eggs in it, buried it and either left the offspring to their own devices or guarded the nest until hatching, similar to crocodiles. Soon or even directly after hatching, the flaplings (what pterosaur-hatchlings are called) were capable of flying and caring for themselves and were not in need of parental care. Of course this may not have applied to all pterosaurs, but the lack of evidence for other parenting methods does not give room to go as far as suggesting viviparous frigate bird-mimics.
Fig. 8: Like in this painting by Zdeněk Burian, pterosaurs are often imagined having taken care of their young, similar to birds. Fossil evidence for this is scarce however. On a side-note, if you ever played Ecco the Dolphin on the Sege Genesis/Mega Drive you may recognize this artwork, as the developers directly ripped it for one of their in-game sprites. 
On a last note, the idea that some archosaurs may have given live-birth has often cropped up on occasion (like in sauropods or the theropod Coelophysis), but so far nearly all prominent claims were able to be disproven, to the point where it is now generally thought that archosaurs are incapable of evolving viviparity. However, there is one archosaur-group, metriorhynchids, for which an argument can be made, as these were fully marine crocodylomorphs which were likely incapable of crawling back on land. It is interesting that pterosaur-eggs seem to have had flexible, leathery shells, more similar to the eggs of lizards, snakes or crocodiles than to those of dinosaurs. As squamates and synapsids have occasionally evolved ovoviviparity, or true viviparity in the case of skinks and mammals, leathery eggshells seem to be a prerequisite for this adaptation. It is therefore perhaps not impossible that some pterosaurs may have evolved forms of viviparity, but still highly improbable.

Edit: I have to add two things, which have been brought to my attention by helpful readers. First there is apparently a paper in which Everhart identifies an unusually wide pelvis in Pteranodon, which he sees as a sign for viviparity. He does not actually mention that in the book (at least not in the version I read), which makes the speculation seem way more out of left field. That said, a wide pelvis has also been used as evidence for viviparity in other archosaurs, like sauropods, without much success. It more likely means that Pteranodon just laid particularly large eggs (which does have interesting implications for parental care). The second thing is that the information about flaplings presented here is largely based on Mark Witton's book Pterosaurs from 2016. Since its release however more evidence has appeared for parental care and altriciality. In general, the question of parental care in pterosaurs is not a clear-cut consensus and parenting styles likely varied from species to species.

Skim-feeding pterosaurs

Rynchops is a modern genus of seabirds with unique jaw-adaptations. Their lower jaw is knife-shaped and a lot larger than the upper one. This allows them to literally plow the ocean-surface for fish by flying low. This is called skim-feeding and seems to be a very rare style of fishing among birds. Yet for some reason nearly every prominent pterosaur-group, from pteranodonts to dimorphodonts, thalassodromids and azhdarchids, has at one point or another been interpreted as skim-feeders. The most prominent example is Rhamphorynchus, the well-known, small, long-tailed pterosaur from the Solnhofen Limestone. Just think back to episode 3 of Walking with Dinosaurs. The idea of skim-feeding pterosaurs, which from the very start was based on wonky science, was dealt a fatal blow in the early 2000s, with numerous studies seriously investigating the idea. The most important one was a 2007 paper by Stuart Humphries and Mark Witton. They showed that the beaks of pterosaurs were so maladapted for skimming that some, like Rhamphorynchus or Thalassodromeus, would have dislocated or even broken their jaws if they attempted to skim-feed like Rynchops. It is far more likely that sea-going pterosaurs caught fish simply by dip-feeding or spearing them with their teeth rather than skimming. Some may have even swam after their prey.
Fig. 9: The great artist C.M. Kosemen once imagined what a pterosaur would look like if it had a similar style of feeding to Rynchops and called this speculative creation Anomalorhynchus. There is no real known pterosaur from the fossil record that actually looked like this.
The idea that most or all pterosaurs were fish-eaters is also one that is strangely widespread, perhaps being linked to the idea that they required cliffs and thermal winds to take off and therefore had to live close to the sea. In reality pterosaurs show adaptations for a wide variety of diets. Azhdarchids and thalassodromids were likely terrestrial predators of small animals, istiodactylids show adaptations towards scavenging, Pterodaustro was a flamingo-like filter-feeder, dimorphodontids and anurognathids were probably insectivores and campylognathoidids had jaws capable of chewing, which may have even allowed them to eat plant-matter on occasion.

David Peters in general

David Peters started out in the early 90s as a very talented paleoartist, perhaps with the potential to become the next Greg Paul. Around 1995 something went awfully wrong, however. As he was not a trained paleontologist, he designed his very own method of examining fossils… or more accurately photographs of fossils, as he has never directly worked with the fossils concerned. He calls it Digital Graphic Segregation and it basically amounts to just color-coding random artefacts on the photograph in photoshop, which Peters, powered by pareidolia, then interprets as genuine features of the fossil. Through this rather dubious method, Peters has come to conclusions that in ridiculousness put everything mentioned previously to shame. He thinks that pterosaurs were covered in a multitude of large ribbon- or feather-like scales or even anglerfish-like lures, that they were bipedal, that their wing-membranes were extremely narrow (I am reminded of dragonflies), that toothless pterosaurs actually had teeth, that they are closely related to Triassic weirdos like Longisquama and Sharovipteryx and that they actually descend from squamates, the reptile clade that includes lizards and snakes. He also thinks they were viviparous, giving birth to miniature adults with cartilaginous skeletons, and has identified some species as flightless or even as blood-sucking parasites. He does not stop at pterosaurs but has gone on to try and redefine the entire tetrapod family-tree, claiming that synapsids are close relatives of archosaurs, among other things.
Fig. 10: In 2008 C.M. Kosemen and John Conway tried to draw pterosaurs based entirely on David Peters’ skeletals and methods. This was the result. Left is supposed to be Pterodactylus and right Pteranodon, in case you couldn’t tell.
Needless to say, the scientific community does not take Peters seriously and his claims have never passed peer-review. Instead of taking this as a sign for introspection, Peters instead went for the common mix of Galileo Gambit and Dunning Kruger Effect, thinking that his methods are superior to everyone else’s and that he is not being taken seriously because established scientists are conspiring against him to protect their status. He therefore went online and presented his work on his two websites, ReptileEvolution.com and ThePterosaurHeresies.com. If you are googling an obscure, extinct reptile, like say Cosesaurus, there is a high chance that among the highest search-results will be a link to one of his websites. As Peters is a great artist with a good feeling for web-design, many unsuspecting people who do not know any better will read those, thinking he is an authority on these matters, and go on to be severely misinformed. Zoologist Darren Naish and paleoartist Nima wrote great articles summing up all the problems mentioned here far better than I could. I linked them below, so I definitely recommend you to go read them. Last I heard, Peters is currently more focused on mammals, claiming that multituberculates are rodents and that rodents are marsupials. Good luck with that.

Literary sources:

  • Bakker, Robert Thomas: The Dinosaur Heresies. New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction, New York 1986.
  • Everhart, Michael J.: Oceans of Kansas. A Natural History of the Western Interior Sea, Bloomington 2005 (Second Edition).
  • Owen, Richard: Geology and Inhabitants of the Ancient World, London 1854 (Facsimile Edition).
  • Seeley, Harry Govier: Dragons of the Air. An account of extinct flying reptiles, London 1901.
  • Wagler, Johann Georg: Natürliches System der Amphibien. Mit vorangehender Classification der Säugethiere und Vögel, München 1830.
  • Wellnhofer, Peter: The Illustrated Encyclopedia of Pterosaurs. An illustrated natural history of the flying reptiles of the Mesozoic Era, New York 1991.
  • Witton, Mark: Pterosaurs, New Jersey 2013.
  • Witton, Mark: Recreating an Age of Reptiles, Marlborough 2017.

Papers:

Online sources:


Image Sources:
  • Fig. 1: Schalansky, Judith: Die Verlorenen Welten des Zdeněk Burian, Berlin 2013, p. 160 (Naturkunden 8).
  • Fig. 2: Wellnhofer, Peter: The Illustrated Encyclopedia of Pterosaurs. An illustrated natural history of the flying reptiles of the Mesozoic Era, New York 1991, p. 27.
  • Fig. 3: Wikimedia
  • Fig. 4: Wikimedia
  • Fig. 5: Bakker, Robert Thomas: The Dinosaur Heresies. New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction, New York 1986, p. 456.
  • Fig. 6: Dixon, Dougal: The New Dinosaurs. An Alternative Evolution, London 1988, p. 34.
  • Fig. 7: Witton, Mark: Pterosaurs, New Jersey 2013, p. 66.
  • Fig. 8: Schalansky, Judith: Die Verlorenen Welten des Zdeněk Burian, Berlin 2013, p. 160 (Naturkunden 8), p. 159.
  • Fig. 9: C.M. Kosemen's old tumblr blog
  • Fig. 10: Why the world has to ignore ReptileEvolution.com by Tetrapod Zoology (Ver. 3).

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