Feathered pterosaurs: ruffling the feathers of dinosaur evolution
In December 2018, researchers claimed to have found featherlike structures in two specimens of pterosaurs.1 These appendages, called pycnofibres when found in pterosaurs, were said to resemble non-vaned group filaments and bilaterally branched filaments—structures previously thought to be unique to maniraptoran dinosaurs and which have been previously used as evidence that some dinosaurs had feathers. The researchers claim that these pycnofibres are diagnostic of feathers. However, of the four types of pycnofibres they identified in one pterosaur, three were said to be similar to ‘protofeathers’ previously thought to be unique to unrelated groups of dinosaurs. But why would all these diverse dinosaur ‘protofeather’ types be present in one single pterosaur specimen? This paper compares decayed collagen fibres in marine fossils to these pterosaur ‘pycnofibres’ and suggests that these integumentary structures are identical. But if these pterosaur ‘pycnofibres’ are nothing more than decayed collagen fibres, so too are the three types of dinosaur ‘protofeathers’ associated with it. This presents a challenge for those who choose to interpret ‘dino fuzz’ as evidence of feathered dinosaurs.
History of evolutionary thought on the origin of birds
Dinosaurs are a unique class of terrestrial (i.e. ground-dwelling) reptiles. Thus, pterosaurs are not dinosaurs but flying reptiles. Nevertheless, to understand why some evolutionary researchers think that pterosaurs were feathered, we need to trace the history of ‘feathered dinosaurs’.
As far back as 1868, evolutionists such as Thomas Huxley taught that birds evolved from dinosaurs long before there was any evidence of fossil ‘feathered dinosaur’ candidates. So it was a theory that had little supporting evidence.
In the 1980s, Jacques Gauthier injected new life into the debate by presenting a more nuanced cladistical model where he argued that theropod dinosaurs evolved into modern birds.2 Many evolutionists regarded Gauthier’s paper as pivotal to the idea that theropod dinosaurs evolved into birds, and his paper is still often cited by evolutionists today.
In 1996, a dinosaur fossil (Sinosauropteryx) was found that featured a fuzzy vagueness along its back and on various parts of its body (figure 1). Evolutionists declared that this hairlike feature showed that some dinosaurs evolved into birds and that the fuzzy structure were some kind of protofeathers or precursor to bird feathers. In their published paper, the authors declared that the fuzz resembled modern bird feathers and they may have been hollow. However, they also added a caveat. They wrote: “the… [fuzzy] structures are piled so thick that it has not been possible to isolate a single one for examination”.3 Neither light microscopy nor detailed examination of these structures were carried out. Are these really feathers?
So, what are these fuzzy structures? In 2007, two secular scientists, Theagarten Lingham-Soliar and Alan Feduccia, teamed up to study these integumentary structures in detail. They examined this ‘dino fuzz’ using scanning electron microscopy and came to a surprising conclusion—the fuzzy structures were neither feathers, nor were they hollow, but were instead identical to partially decayed collagen fibres in skin. Feduccia even noted that the ‘dino fuzz’ on Sinosauropteryx was not even on the surface of the creature but within the confines of the body outline.4
The duo carried out further experiments including burying dolphin carcasses for a year before studying them in their partially decayed state with SEM and chromatographic analysis. They compared the ‘dino fuzz’ in Sinosauropteryx with similar structures found in fossil pterosaurs, fossil ichthyosaurs, and decayed carcasses of dolphins and sharks. All these creatures presented identical hairlike structures on their fossils/carcasses. But ichthyosaurs, dolphins, and sharks do not fly, nor do they have feathers!
On the dolphin carcasses, Lingham-Soliar noted that:
“These degraded fibres presented almost limitless pattern permutations, in many instances showing featherlike patterns that are strikingly similar to many of those identified as protofeathers in the Chinese dromaeosaurs and including a wavy appearance of the allegedly external ‘appendages’ reported in the fibres preserved with the Early Cretaceous dromaeosaur Sinornithosaurus millenii, which Richard Prum cited as illustrating a critical stage in his filament-to-feather evolution model.”5
They also examined several pterosaur fossils and noted that many of them displayed features identical to what was present in both dinosaur as well as marine reptiles.
“To add to the confusion, the same fibrelike structures of Sinosauropteryx are found in a primitive ceratopsian (ornithischian) dinosaur, Psittacosaurus, and another unrelated ornithischian, a group thought to have no relation to the origin of birds, as well as a variety of pterosaurs from various ages and localities, including the Early Cretaceous Chinese rhamphorhynchoid pterosaur Jeholopterus.”6 [Notice that these authors mention that pterosaur fuzz is similar to what we see in dinosaurs.]
“A miscellany of pterosaurs, including primarily pterodactyloids, and a few rhamphorhynchoids, some, such as Jeholopterus, exhibiting ‘hairs’ resembling the hairlike integumentary filaments of the dinosaur Sinosauropteryx. There is also the very small, arboreal pterosaur Nemicolopterus … .”7
After detailed examination of alleged ‘dino fuzz’ they concluded that all reported cases of protofeathers in dinosaurs, marine reptiles, and flying reptiles alike, “show a striking similarity to the structure and levels of organization of dermal collagen. The proposal that these fibres are protofeathers is dismissed.”3 What was previously identified as pycnofibres in pterosaurs turned out to be just “collagen and keratin structural fibres” (figure 2).8
Lingham-Soliar’s and Feduccia’s work is currently the most detailed study on the taphonomy of integumentary structures.10 Yet for most part, a lot of their work has been deliberately ignored by evolutionists for good reason—if these strandlike structures are common in dinosaurs, flying reptiles, marine reptiles, sharks, and even dolphins, they cannot be feathers and they convey no evolutionary significance. But for many evolutionists, ‘feathered dinosaurs’ have become a sort of religious dogma for the origin of birds. If these fossil artefacts were to be reduced to just collagen fibres, the central lynch-pin in dinosaur-to-bird evolution collapses. As Gauthier, a critic of Feduccia, admits: “We basically try and ignore [Feduccia]. For the dinosaur specialists, it’s a done deal [i.e. the idea that dinosaurs developed feathers and evolved into birds], … the bird people trust him, and so he’s poisoning his own discipline.”11
Unfortunately, since the 1996 paper that alleged to have found protofeathers in Sinosauropteryx, other evolutionists have been quick to attribute every kind of fuzzy appearance in dinosaur fossils to feathers without regard to its dermal taphonomy.
As Storr Olson, Emeritus Curator of Birds at the Smithsonian’s National Museum of Natural History, explains:
“The idea of feathered dinosaurs … is being actively promulgated by a cadre of zealous scientists acting in concert with certain editors at Nature and National Geographic who themselves have become outspoken and highly biased proselytizers of the faith.”12
Pycnofibres: filamentous structures in pterosaurs
But what have alleged dinosaur ‘protofeathers’ got to do with pycnofibres in pterosaurs? When these filamentous structures are present in pterosaurs, they are called pycnofibres. Pycnofibres have been reported in various specimen of fossil pterosaurs as far back as 1831—even before alleged ‘protofeathers’ were identified in Sinosauropteryx.13 The current popular interpretation of pycnofibres as some type of dino fuzz in pterosaurs has been especially popular since 1971.14 Since that time, numerous papers have been published that concluded that these simple hairlike artefacts were anything from flexible short hairlike fibres to antecedents of protofeathers.
In 2015, Theagarten Lingham-Soliar concluded in his comprehensive two-volume work on The Vertebrate Integument that what has commonly been identified as protofeathers in dinosaurs were very likely to be just collagen fibres from partially decayed skin.15 He concluded that the strandlike integumentary structures seen in pterosaurs are identical to those found in Sinosauropteryx as well as several other Chinese taxa, and these are all unlikely to have anything to do with feathers.16 This poses a conundrum for evolutionists—how can the fuzzy structure in dinosaur fossils be protofeathers if the exact same structures are also found in not only dinosaurs, but also pterosaurs and marine creatures not regarded as on the evolutionary line to birds?
In The Riddle of the Feathered Dragons, Alan Feduccia explained:
“Given that Xu and colleagues suggested that there is ‘a potential primary homology among the integumentary feathers’ of theropods such as Beipiaosaurus, the ornithischians Psittacosaurus and Tianyulong, and some pterosaurs, such a proposal would ‘push the origin of monofilamentous integumentary structures into the Middle Triassic at least’. As has been noted, some pterosaurs share filamentous structures indistinguishable from the dino-fuzz present on so many of the Early Cretaceous fossils and most recently Zheng and colleagues have included still another ornithischian, the heterodontosaurid Tianyulong, to the list of dinosaurs and archosaurs associated with feather origins, ranging from herbivores and small meat-eating coelurosaurs to the large, flesh-eating tyrannosauroids [emphasis added].”17
Note that this quote from Feduccia’s book was written six years before the recent 2018 article—but Feduccia’s work was never cited in the recent 2018 publication which declared that pterosaurs had ‘protofeather’/furry covering. In other words, it has been known for quite a while that the partially decayed collagen fibres of marine reptiles and mammals, are indistinguishable from pycnofibres in pterosaurs and protofeathers in dinosaurs.
Compare the drawing of decayed collagen in ichthyosaur with the branching pattern of pterosaur pycnofibre in figure 3. Also, compare the photos within figure 4 and within figure 5.
Protofeather advocates have previously tried to argue that the hairlike structures found in dinosaurs are protofeathers, and that these are different from the furry structures seen in pterosaurs. When found in pterosaurs, this distinction is made by calling them pycnofibres. It is claimed that pycnofibres are different from what is seen in marine reptiles, sharks, and dolphins, even though (as demonstrated in the photos) these structures appear almost identical. What sets this recent December 2018 paper apart from previous papers on pterosaur pycnofibres is that this paper claimed that these are feathery structures, yet at the same time acknowledges that their pterosaur specimen had structures previously thought to be unique to certain specific groups of dinosaur fossils. They grouped the pycnofibres in their pterosaur specimen into four categories, three of which are similar to what has been observed in dinosaurs.22
The four types of pterosaur pycnofibres were described as:23
Type 1: Resembling monoﬁlaments in the ornithischian dinosaurs Tianyulong and Psittacosaurus and the coelurosaur Beipiaosaurus.
Type 2: Resembling the brushlike bundles of ﬁlaments in the coelurosaurs Epidexipteryx and Yi.
Type 3: Resembling bristles in modern birds, but did not correspond to any reported morphotype in non-avian dinosaurs.
Type 4: Identical to the radially branched, downy featherlike morphotype found widely in coelurosaurs such as Sinornithosaurus, Beipiaosaurus, Protarchaeopteryx, Caudipteryx, and Dilong.
Type 1, 2, and 4 are said to resemble what has been previously observed in dinosaur fossils. Type 4 is the dense downy filaments that are alleged to have covered the wings of these pterosaurs.
Whether this classification is accurate would require another paper altogether, and there is good reason to believe that this classification is inaccurate. For example, photos of the actual pterosaur filaments appear ‘strandlike’ in contrast to the covering of Protarchaeopteryx and Caudipteryx (which were probably secondarily flightless birds rather than dinosaurs) which have been found with pennaceous feathers, and these are again quite different from the rodlike structures seen in Beipiaosaurus (therizinosaur).24-25 Yet the paper classifies Protarchaeopteryx, Caudipteryx, and Beipiaosaurus together as Type 4 feathers. However, for the sake of argument, in this paper, we will assume that the classification of the four types of feathers is accurate. Even then, the authors point out that three out of four types of pterosaur pycnofibres found match those previously thought to be unique to some types of dinosaurs. So why are all these unique types of protofeathers/pycnofibres found together in one single specimen of pterosaur?
The most parsimonious explanation for such a phenomenon is that these fine structures are just permutations of the same original integumentary gross structure. That is, these are just typical shapes of degraded collagen fibres. But if these structures are just collagen fibres, then so too are the same structures when found in dinosaurs featuring Types 1, 2, and 4. Since feathered dinosaurs are non-negotiable for many evolutionists—instead of admitting that dinosaurs did not have feathers, they turn around and claim that these pterosaurs must likewise be covered in feathery, hairlike structures. But this explanation still fails to explain the presence of these structures in marine reptiles, sharks, and dolphins, or why one completely unrelated creature (i.e. a pterosaur) would have similar integumentary structures previously assumed to be unique to so many different groups of dinosaurs.
The researchers in the feathered pterosaur paper acknowledged that they did not know the ‘affinities and function’ of these pycnofibres and even acknowledged that these structures appeared to take on a variety of different forms depending on where they are found on pterosaurs. But that did not stop the authors from speculating further that these structures may have played a role in thermoregulation, tactile sensing, signalling, and aerodynamics. But this imaginary function is nothing more than a just-so story not supported by any scientific evidence. If anything, the presence of a furry covering on the wing membrane is likely to be maladaptive as the following discussion will show.
Hairlike structures on wing membranes are maladaptive
In birds today, baby ostriches are known to be vulnerable to hypothermia and may die if they are caught in the rain without shelter from their mother’s wings. This may have been even more problematic for flight-capable pterosaurs since such a furlike covering would become wet in the rain and accelerate body heat dissipation. The developmental objective is for ostriches to outgrow this stage of feather development as soon as possible.26
Hair is not aerodynamic, and it is likely to pose a problem for flight. For example, bats are covered with fur on some parts of their bodies, but the main aerodynamic parts of their wing membranes are almost entirely hairless. The wing membrane in bats mainly consists of a thin but strong collagenous and elastic fibre centre, probably not too unlike pterosaurs. Even then, if bats are caught in rain, they spend 20 times more energy during flight than at rest, compared to 10 times more energy during flight when dry, because they need more energy to keep their bodies warm, and because their fur clumps together when wet, making them less aerodynamic.27 How much more energy would a pterosaur have to expend if not just their body and head, but if their entire wing membranes were covered in a thick furry layer of pycnofibres?
The intricacies of flight are well known. Many birds have an alula—usually three to five thumb feathers on the leading edge of the wing that reduces drag when the bird is flying at low speeds. A single feather alone can make a big difference to its flight capability. Yet now we are to assume that a pterosaur had dense furry non-aerodynamic hairline structures on its entire wing membrane without impeding its ability to fly! Researchers have the right to speculate on the function of pterosaur pycnofibres—assuming these are indeed dense hairline structures—but they bear the burden of demonstrating that their speculation would not be maladaptive or possibly lethal to pterosaurs.
Melanosome and keratin
The researchers in the 2018 pterosaur paper also claimed to have found evidence of preserved pigment microbodies in two pterosaur fossils—structures responsible for colour. They also claimed to have found roundish carbonaceous microbodies that resembled fossil melanosomes, but this is controversial, and some paleontologists remain skeptical that these roundish microbodies are even melanosomes. Lingham-Soliar for example, has often criticized dinosaur-to-bird evolutionists for automatically labelling as melanosomes all roundish microbodies of a certain size:
“A blanket view that all sinuous structures in the Chinese dinosaurs were ‘protofeathers,’ is now being compounded by a blanket view that all micro-particles found in the same integumental structures are melanosomes.”28
Lingham-Soliar argues that claims to have discovered phaeomelanosomes in fossils and then “divining color [their colour] … are totally without merit.”28
But even if we grant that these are indeed melanosomes, it still does not prove that these pterosaurs are covered in a featherlike covering. Why? Simply because melanosomes are also found in hair and skin, so their presence is not a diagnostic characteristic of feathers.
Furthermore, two types of melanosomes are often attributed to fossils: rod-shaped eumelanosomes, and the more commonly identified round-shaped phaeomelanosomes. The researchers claimed to have found phaeomelanosomes, but phaeomelanosomes are not found in any extant reptiles today—so why should we even assume that these microbodies are even melanosomes?
In addition, infrared spectroscopy (FTIR) of the pterosaur specimen was said to be, “more consistent with α-keratin … than β-keratin”.1 But again, α-keratin is found in all vertebrates, and is also present in skin, so this is not diagnostic.
Finally, the authors of the feathered pterosaur article acknowledge that unlike hair and feathers, pycnofibres are “more superficially attached than the deeply rooted hairs of mammals”. 1 All these fit much better with the decayed skin collagen hypothesis.
Rather than showing us that pterosaurs were feathered, the evidence actually shows otherwise. Pterosaur ‘pycnofibres’ are likely just collagen and keratin structures in their partially degraded state. The most likely reason why anyone would call these fibres feathers is that they are indistinguishable from what was previously identified as protofeathers in dinosaurs.
Conversely, if these pterosaurs were not feathered, neither were dinosaurs. This would demolish the central pillar in dinosaur-to-bird evolution. Thus, in order to avoid this conclusion, some evolutionists now claim that pterosaurs must have likewise been covered in a protofeatherlike covering. However, this explanation is inadequate since the integumentary structures are also found in decaying carcasses and fossils of featherless sharks, marine reptiles, and dolphins.
To consistently maintain the idea of feathered pterosaurs, three conclusions present themselves:
- ‘Convergent evolution’ of feathers multiple times—once in Aves, then again in early ‘stem birds’ such as Archaeopteryx, and then again for pterosaurs. The pterosaurs would then have to independently evolve similar feathery structures identical to three different and unrelated types of ‘dinosaur protofeathers’, and then group them together in one single creature. To put it plainly, it is unscientific wishful thinking; or:
- Push the origin of feathers way back in time before the dinosaurs, to the supposed age of the archosaurs—but this would require first rejecting current theories of dinosaur-to-bird evolution. The two pterosaurs in the paper were dated at 165–160 Ma using evolutionary dates. This would suggest that any supposed common ancestry would have to be pushed even further back in evolutionary time to the Middle Triassic at the very least. Even then, this explanation would not explain why all these different types of ‘protofeathers/pycnofibres’ converge in one single pterosaur. Nor does it explain their similarities to the collagen fibres of marine carcasses in their partially decayed state.
- The most likely conclusion: Admit that these are just collagen fibres. This is the most parsimonious explanation since this would explain why we also observe these filaments in creatures that do not have feathers (i.e. marine creatures). This option carries with it the burden of deleting the best evidence for feathered dinosaurs and poses a serious problem for the evolutionary dinosaur-to-bird paradigm.
As Alan Feduccia explained in Riddle of the Feathered Dragons:
“Given that Xu and colleagues suggested that there is ‘a potential primary homology among the integumentary feathers’ of theropods such as Beipiaosaurus, the ornithischians Psittacosaurus and Tianyulong, and some pterosaurs, such a proposal would ‘push the origin of monofilamentous integumentary structures into the Middle Triassic at least’. As has been noted, some pterosaurs share filamentous structures indistinguishable from the dino-fuzz present on so many of the Early Cretaceous fossils, and most recently Zheng and colleagues have included still another ornithischian, the heterodontosaurid Tianyulong, to the list of dinosaurs and archosaurs associated with feather origins, ranging from herbivores and small meat-eating coelurosaurs to the large, flesh-eating tyrannosauroids.”17
- Yang, Z. et al., Pterosaur integumentary structures with complex feather-like branching, Nature: Ecology & Evolution 3:24–30, Dec 2018. Return to text
- Gauthier, J., Saurischian monophyly and the origin of birds; in: Padian, K. (Ed.), The origin of birds and the evolution of Flight, Memoirs of the California Academy of Sciences 8:1–55, 1986. Return to text
- Lingham-Soliar, T., Feduccia, A., and Wang, X., A new Chinese specimen indicates that ‘protofeathers’ in the Early Cretaceous theropod dinosaur Sinosauropteryx are degraded collagen fibres, Proc. Biol. Sci. 274(1620):1823–1829, 2007. Return to text
- Sarfati, J., Feathered dinos: no feathers after all! J. Creation 26(3):8–10. Return to text
- Feduccia, A., Riddle of the Feathered Dragons, Yale University Press, New Haven, CT, p. 130, 2012. Return to text
- Feduccia, ref. 5, p. 130. Return to text
- Feduccia, ref. 5, pp. 258–259. Return to text
- Lingham-Soliar, T., Structure, design and function; in: The Vertebrate Integument, vol. 2, Springer, Berlin, Germany, pp. 135–138, 2015. Return to text
- Feduccia, ref. 5, p. 134 Return to text
- Lingham-Soliar’s 2015 Magnum Opus on the subject matter is a comprehensive two-volume graduate textbook devoted to The Vertebrate Integument totalling over 600 pages. Feduccia is a leading evolutionary paleornithologist with over 160 publications and a dozen books, including authoring an award-winning textbook, The Origin and Evolution of Birds (winner of the Association of American Publishers 1996 award for Excellence in Biological Science, a Pulitzer Prize candidate, and The National Book Critics Circle Award). Feduccia has also written arguably the most comprehensive book on the subject of ‘feathered’ dinosaurs from China: Riddle of the Feathered Dragons in 2012. Feduccia acknowledges that dinosaurs could not have evolved into birds. As an evolutionist, he pushes the origin of dinosaurs further back in time to the archosaurs. Return to text
- Zalewski, D., Bones of contention, Lingua Franca 6:22–24, 1996. Return to text
- Feduccia, ref. 5, p. 8. Return to text
- Witton, M., Pterosaurs: Natural history, evolution, anatomy, Princeton University Press, Princeton, NJ, p. 51, 2013. Return to text
- Sharov, A.G., New flying reptiles from the Mesozoic of Kazakhstan and Kirgizia, Trudy Paleontologicheskovo Instituta Akademii Nauk SSSR [Works of the Paleontological Institute, Academy of Sciences of the USSR] 130:104–113, 1971. Return to text
- Lingham-Soliar, ref. 8, pp. 149–161. Return to text
- Feduccia, ref. 5, p. 123. Return to text
- Feduccia, ref. 5, p. 135. Return to text
- Feduccia, A., Lingham-Soliar, T., Hinchliffe, J.R., Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence, J. Morphology 266:135, 2005. Return to text
- Lingham-Soliar, ref. 8, p. 265. Return to text
- Feduccia, et al., ref. 18, p. 132. Return to text
- Lingham-Soliar, ref. 8, p. 97. Return to text
- Yang, Z. et. al., ref. 1, p. 5. Return to text
- Yang, Z. et. al., ref. 1, p. 7. Return to text
- Feduccia, ref. 5, pp. 135, 175. Return to text
- Feduccia, ref. 5, p. 276. Return to text
- Feduccia, ref. 5, pp. 121, 137. Return to text
- Voigt, C., Schneeberger, K., Voigt-Heucke, S., and Lewanzik, D., Rain increases the energy cost of bat flight, Royal Society 7(5), 2011. Return to text
- Feduccia, ref. 5, p. 137. Return to text