Naked pterosaurs–or feathered? PhDs clash

Earlier Yang et al. 2019
argued that pterosaurs, like the disc-headed unnamed anurognathids, CAGS-Z070 (Fig. 1) and NJU-57003 (Fig. 2), had protofeathers and thus they were related to dinosaurs with feathers.

Yesterday Unwin and Martill 2020 
argued that pterosaurs did not have protofeathers. They said, any feathery-looking remains are decomposing fibers shed from the wings. They note that bristle-like integumentary structures do fringe the jaws of CAGS-Z070, but they do not concede any sort of homology other than to call the bristles ‘bristles’.

Yesterday Yang et al. 2020
replied to Unwin and Martill 2020, defending their hypothesis. “In our [2019] paper, we explored the morphology, ultrastructure and chemistry of the dermal structures of pterosaurs and showed that they probably had a common evolutionary origin with the integumentary structures seen widely in dinosaurs (including birds), their close relatives.” 

Their first sentence is wrong. As long-time readers are tired of hearing by now, Peters 2000, 2007 tested the pterosaur – dinosaur relationship by adding taxa. The added taxa attracted pterosaurs away from dinosaurs and nested them in a new and overlooked third clade of lepidosaurs, the Tritosauria, of which late surviving Huehuecuetzpalli is a basal member.

Yang et al. 2020 remind us,
“all four pycnofibre types are morphologically identical to structures already described in birds and non-avialan dinosaurs, not only in terms of gross morphology but also in their ultrastructure and chemistry, including melanosomes and chemical evidence for keratin; collectively, thesefeatures are consistent with feathers.”

Or hair. Or scales. Does anyone else see Yang et al. “Pulliing a Larry Martin“? The first thing Yang et al. should do is establish the relationship of pterosaurs with more parsimonious outgroups. They should know convergence is rampant within the Vertebrata and pterosaurs have never nested with dinosaurs whenever other candidates have been offered.

“Mapping these data onto a phylogeny yields a single evolutionary origin for feathers minimally in the avemetatarsalian ancestor of both pterosaurs and dinosaurs.”

That’s what happens when you omit data and citations. Professor Michael Benton is on the list of authors. This is not the first time Benton has omitted data and citations. You might remember when Hone and Benton 2008, 2009 were going to test competing hypotheses of relationship of pterosaurs. They reported they would test the archosaur hypothesis of Bennett 1996 versus the non-archosaur hypothesis of Peters 2000. Peters tested four prior hypotheses (including Bennett 1996) by simply adding Longisquama (Fig. 5), Cosesaurus, Sharovipteryx, and Langobardisaurus (Fig. 6), all of which attracted pterosaurs to their clade. Several of these added taxa have pterosaur-like fibers on their bodies (Fig. 5). When the anticipated results did not go their way, Hone and Benton 2009 deleted all reference to Peters 2000 and wrote that Bennett 1996 had come up with both competing hypotheses.

Getting back to the Reply from Yang et al. 2020:
“In their comment, Unwin and Martill [2020] assert that the branched integumentary structures that we identified are not feathers or even pycnofibres. They make five arguments in favour of their point of
view:”

1. “superposition or decomposition of composite fibre-like structures or aktinofibrils yields branched structures similar to those in the anurognathids;
2. the anatomy and anatomical distribution of the anurognathid integumentary structures are consistent with aktinofibrils, but not pycnofibres;
3. evidence for keratin and melanosomes is not indicative of pycnofibres but rather reflects contamination from epidermal tissue;
4. the branching we reported is not consistent with exclusively monofilamentous coverings in other anurognathids; and
5. homology of the branched integumentary structures with feathers cannot be demonstrated conclusively owing to the simple morphology of the former.”

“We refute all five of their arguments.”

The view from ReptileEvolution.com:
Apparently no one has noticed that anurognathids, like Jeholopterus (Fig. 3), are decidedly different than other pterosaurs in terms of the length and quantity of their feathery fluff. In this way, and many others, anurognathids resemble modern owls, predator birds capable of silent flight due to the fluffiness of the pelage.

It is also worth noting
that anurognathids leave no descendants after the Early Cretaceous. In any case, pterosaurs are not related to birds or dinosaurs or archosaurs or archosauriformes or archosauromorphs, as demonstrated in the large reptile tree (LRT, 1740+ taxa) which tests all candidates for dinosaur, bird and pterosaur ancestry back to headless Cambrian chordates.

A figure caption from Unwin and Martill 2020
(Fig. 4) reports, “The inner region of the cheiropatagium adjacent to the body anterior to the pelvis. The dark, slightly granular epidermal surface of the integument (et) covering the torso (t) contrasts with the remarkably thin epidermal surface (ep) of the integument forming the proximal region of the cheiropatagium (c). Much of the epidermis covering the cheiropatagium has been lost, exposing closely packed and aligned aktinofibrils (ak) now slightly decayed. On the far left, much of the cheiropatagium has been pulled away, leaving a few incomplete aktinofibrils and numerous fine fibrils (fb) from which they were composed.”

This is the PIN–2585/36 specimen of Sordes pilosus, which Unwin has not shown in its entirety—ever. The proximal membrane (yellow) is the left fuselage fillet (see Fig. 3), which disproves the batwing hypothesis championed by Unwin and other PhDs. Unwin and Martill say the fine fibrils at left have been ‘pulled away’. I know of no fossil processes that ‘pull’ fine fibrils away from their original insertion points.

Other Sordes specimens have been misinterpreted by Unwin since Unwin & Bakhurina 1994. Peters 1995 argued against the bat-wing interpretation offered by Unwin & Bakhurina 1994 further described nine years ago here.

Yang et al. 2020 conclude:
“In light of this, the most parsimonious interpretation of the simple and branched integumentary appendages in the anurognathid pterosaurs remains our original conclusion that they are feathers.”

This conclusion is not supported by the LRT. Taxon inclusion would have helped Yang et al. 2020. Unwin and Martill 2020 are likewise not correct. They should have shown the same evidence that Yang et al. presented was incorrect, rather than showing their own evidence, which does not support their position.

An online article posted on Phys.org
cites U of Leicester and U of Portsmouth (England) workers. David Unwin and David Martill who claim pterosaurs “were in fact bald.”

The article reports, “Feathered pterosaurs would mean that the very earliest feathers first appeared on an ancestor shared by both pterosaurs and dinosaurs, since it is unlikely that something so complex developed separately in two different groups of animals.”

Unlikely ≠ impossible. Just cite the LRT where convergence is rampant. Adding taxa is something paleontologists have been loathe to do for the last twenty years since Peters 2000 moved pterosaurs away from dinosaurs and 13 years since Peters 2007 moved pterosaurs into lepidosaurs. But let’s move on…

The article then states, 
“It would also suggest that all dinosaurs started out with feathers, or protofeathers but some groups, such as sauropods, subsequently lost them again—the complete opposite of currently accepted theory.” 

Once again, add taxa to determine where feathers, or protofeathers, first appeared in tetrapods and if there was a second genesis within the clade.

The article then states,
“The evidence rests on tiny, hair-like filaments, less than one tenth of a millimeter in diameter, which have been identified in about 30 pterosaur fossils. Among these, Yang and colleagues were only able to find just three specimens on which these filaments seem to exhibit a ‘branching structure’ typical of protofeathers.”

Evidence from 30 or just 3 pterosaurs is considerable. Nevertheless, all prior authors omit the pre-pterosaurs (Cosesaurus, Oculudentavis, Sharovipteryx, Longisquama, Fig. 5) most of which have epidermal membranes and fibers. These taxa (Fig. 6) nest between pterosaurs and the lepidosaur Huehuecuetzpalli.

The Phys.org article then states,
“Unwin and Martill propose that these are not protofeathers at all but tough fibers which form part of the internal structure of the pterosaur’s wing membrane, and that the ‘branching’ effect may simply be the result of these fibers decaying and unraveling.”

Professor Unwin said:
“The idea of feathered pterosaurs goes back to the nineteenth century but the fossil evidence was then, and still is, very weak. Exceptional claims require exceptional evidence—we have the former, but not the latter.”

Professor Martill noted:
that either way, palaeontologists will have to carefully reappraise ideas about the ecology of these ancient flying reptiles. Martill said, “If they really did have feathers, how did that make them look, and did they exhibit the same fantastic variety of colors exhibited by birds. And if they didn’t have feathers, then how did they keep warm at night, what limits did this have on their geographic range, did they stay away from colder northern climes as most reptiles do today. And how did they thermoregulate? The clues are so cryptic, that we are still a long way from working out just how these amazing animals worked.”

As a final note, let’s remember, that when it comes to pterosaur origins, 
workers have been keeping their blinders on for decades. Not sure why, but what results is the current misunderstanding expressed by Yang et al. 2020 AND Unwin and Maritill 2020.

References
Peters D 1995. Wing shape in pterosaurs. Nature 374, 315-316.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371, 62–64.
Unwin DM and Martill DM 2020. No protofeathers on pterosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01308-9
Yang Z et al. 2019. Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution 4, 24–30 (2019).
Yang Z et al. 2020. Reply to: No protofeathers on pterosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01308-9

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