Late Jurassic pterosaur Sordes pilosus, described in 1971, was one of the first pterosaurs confirmed to have a filamentous body covering. But are pterosaur filaments tied to those of dinosaurs, or independently evolved?

What influence do fuzzy pterosaurs have on dinosaur skin evolution? Seemingly, quite a bit. The tree on the left shows integument likelihoods (pie charts) where pterosaurs are considered scaly, tree on the right shows a filamentous analysis. Modified from Barrett et al. (2015).

Was Scleromochlus taylori scaly? Maybe - weakly preserved structures on several specimens seem to suggest so. On this diagram, from Benton (1999), possible transverse scales can be seen on the left and middle specimen.

Laquintasaura venezuelae 2015 edition: basically the same picture, but a bit fluffier, and a bit greener.

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References

Andres, B., Clark, J. M., & Xing, X. (2010). A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs. Journal of Vertebrate Paleontology, 30(1), 163-187.

Barrett, P. M., Butler, R. J., Mundil, R., Scheyer, T. M., Irmis, R. B., & Sánchez-Villagra, M. R. (2014). A palaeoequatorial ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society of London B: Biological Sciences, 281(1791), 20141147.

Barrett, P. M., Evans, D. C., & Campione, N. E. (2015). Evolution of dinosaur epidermal structures. Biology letters, 11(6), 20150229.

Czerkas, S. A., & Ji, Q. I. A. N. G. (2002). A new rhamphorhynchoid with a headcrest and complex integumentary structures. Feathered Dinosaurs and the origin of flight, 1, 15-41.

Frey, E., Tischlinger, H., Buchy, M. C., & Martill, D. M. (2003). New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. Geological Society, London, Special Publications, 217(1), 233-266.

Kellner, A. W. (2003). Pterosaur phylogeny and comments on the evolutionary history of the group. Geological Society, London, Special Publications, 217(1), 105-137.

Ji Q., & Yuan C. (2002) Discovery of two kinds of protofeathered pterosaurs in the Mesozoic Daohugou Biota in the Ningcheng region and its stratigraphic and biologic significances. Geol. Rev. 48, 221–224.

Sharov A, G. (1971). New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. - Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].

Unwin, D. M. (2003). On the phylogeny and evolutionary history of pterosaurs. Geological Society, London, Special Publications, 217(1), 139-190.

Studies into pterosaur and dinosaur filament homology remain thin on the ground, and much of what has been said thus far is reliant on gross filament morphology. Earlier this year, a team of researchers (Barrett et al. 2015) tackled the issue of ornithodiran filament evolution quantitatively, estimating the likelihood of homology between theropod, ornithischian and pterosaur integuments via their distribution on the ornithodiran tree. Using 18 different variations in methods, calculations and data values, they predicted the likelihood of ancestral integument states in dinosaurs and ornithodirans: were they scaly, filamentous, or feathered? The result, announced in not only the paper but also a subsequent media release, was that 12 of those 18 assessments suggested scales were ancestral to ornithodirans, and the filaments seen in pterosaurs, ornithischians and theropods were derived independently from a common scaly ancestor.This conclusion was undoubtedly surprising to some and, indeed, a clear caveat accompanies it: scaly ancestral dinosaurs are "sensitive to the outgroup condition in pterosaurs". Support for ancestrally-scaly ornithodirans relies on the assumption that pterosaur ancestors were also scaly. This condition assumed for 50% of those 18 assessments to account for uncertain ancestral condition for pterosaur integument. In the 9 analyses where pterosaurs were treated as wholly filamentous - and thus consistent with what we see in existing pterosaur fossils - six returned results indicating an ambiguous scaly/filamentous ancestral condition for ornithodirans and dinosaurs, and only 3 supported a wholly scaly interpretation. Of those six 'ambiguous' results, most reported a strong likelihood of ornithodirans being ancestrally filamentous, and many gave dinosaurs a good chance of being ancestrally filamentous too. Moreover, treating pterosaurs as filamentous has knock-on effects through the dinosaur tree: suddenly, there are reasonable, or at least equivocal, chances that ornithichians and saurischians were also ancestrally filamentous. This is a different conclusion to the straighter story of ornithodirans and dinosaurs simply being ancestrally scaly.Clearly, the crux of all this is the assumption that pterosaur ancestors were scaly: just how defendable is this? Because we know little about pterosaur origins, it's hard to say anything conclusive about the evolution of pterosaur integument with our current fossil record. The stratigraphically oldest pterosaur fossil with pycnofibres is from Middle/Late Jurassic deposits, and thus about 50-60 million years younger than the oldest pterosaur fossils - little help in determining if the first pterosaurs were fuzzy. Ongoing disagreements over pterosaur phylogeny complicate attempts to estimate the appearance of lineages with confirmed pycnofibres. Some schemes (those derived from Kellner 2003 and Unwin 2003) suggest pycnofibres must have appeared by the Triassic, close to or at the base of pterosaur ancestry, but others (e.g. Andres et al. 2010) indicate pycnofibres reliably extend no further than the Lower Jurassic. Of course, such assessments of filament distribution might not even be meaningful at this stage, given that pycnofibres are very rare components of pterosaur fossils. They are nowhere near as common as other soft-tissues, such as wing membranes, and we should probably be cautious about any assessment of their evolutionary pathways until we have more data. Perhaps the only significant observation we can make from our current, limited dataset is that, to date, no pterosaur is known with a scaly body covering, even when regionalised scalation - foot pads - preserves in their fossils (Frey et al. 2003).A possible pterosaur relative with scaly hide is known: the Triassic archosaur. Benton (1999) described structures interpreted as thin, transversely orientated scales across the back of multiple specimens of this animal. This might provide vindication of the scaled pterosaur ancestor model, but, again, there are some caveats with this idea. For one,fossils are not well preserved. The scales are feint sediment impressions, visible only in strong, low angle light, such that that they are only considered 'probable' integument impressions by Benton (1999). Previous workers have interpreted them in a different way (as gastralia). Clearly, the evidence for them being scales could be more compelling, and there's certainly not much to work with if we want to test their identification. Secondly, exactly howis related to pterosaurs is not precisely agreed. Some workers consider it the sister taxon of Ornithodira, others as a member of the pterosaur branch, and others see it as more closely related to dinosaurs than pterosaurs. That might seem a minor issue, but we've already seen how sensitive models of ornithodiran integument are to changes of single variables at the base of the tree. We would probably need to run many variants of the integument probability calculations to account for all the uncertainty surrounding. This might give more idea of the range of possible integuments at the base of ornithodiran evolution, but that's not much of an improvement on our current situation.In all, I feel like we're hitting a bit of a wall here. It seems we just don't know enough, and have too many caveats with the limited data we have, to make even a half convincing best guess on this. Thus, how much weight we put on models of ornithodiran integument using scaly pterosaurs is almost a philosophical issue. From my end, I don't think they should be used to argue for scaly ornithodiran and dinosaurian ancestors, at least not with the same weight as tests made using a filametnous pterosaur lineage. When reconstructing ancestral states, characters objectively observed in fossils have to trump assumed character states, even if we know that our dataset is full of holes. After all, the whole point of attempting to figure out an ancestral state is establishing links between character data we have, so introducing opposing character states seems a little contrary to that objective. To be clear, I'm not saying that running models with scaly pterosaur ancestors is a waste of time. To the contrary, it's a good test of model robustness, and Barrett et al. (2015) certainly demonstrate how sensitive our models of ornithodiran integument evolution are by using this approach. Their hypothetical scaly pterosaurs demonstrate that we really do need more early ornithodiran fossils to understand ornithodiran skin evolution. However, I do not think that results of the scaled pterosaur analyses are as informative as their other assessments, as we have to overlook existing data to consider them equally valid.With all that said, do pterosaur fossils really help us understand the evolution of dinosaur filaments? Playing the conservative card here, it seems they do not provide super strong evidence for an all-fuzzy Dinosauria, but they certainly make it difficult to defend ideas of entirely scaly dinosaur ancestors. Forcibly arguing for either scales or filaments at the base of Dinosauria seems premature at this stage, and, whatever our personal hunches are, it seems sensible to accept some ambiguity in this situation for now.I began this article with myconumdrum: how did that play out when, apparently, I can't make up my mind about this scales and filaments debate? Well, I've argued elsewhere that palaeoart can do no better than illustrate credible interpretations of the past and that, so long as the hypotheses they depict are sound, they're doing OK. When we have conflicting or ambiguous hypotheses, we just have to make a judgement call based on our own opinions, gut feelings and interpretations of existing arguments. With my own leaning being towards data showing that scales may not be ancestral to ornithodirans, but also knowing that some dinosaurs are mosaics of filaments and scales, I decided to partially enfluffen my, while leaving their snouts, tails and limbs scaly. I'll leave you with the revised image.Production of the imagery and article seen here was sponsored by my awesome Patrons, who back me at Patreon . As a bonus, they're getting to see the full version of thatimage, along with other rewards and benefits including more exclusive content, discount print prices and other neat stuff. If that sounds like something you're interested in, you can get involved for as little as $1 a month. A huge thanks to those who have signed on already!