SVP abstracts 26: Pterosaur fibers or lack thereof, again

Unwin and Martill 2020
published on this abstract earlier last year and this year (2020).

“Fiber-like structures are frequently preserved in association with fossilized remains of the pterosaur integument. Several fiber types have been recognized. Among the commonest are aktinofibrils, typically 40–100+ μm in breadth and present throughout the flight patagia, exhibiting the same patterns of alignment across Pterosauria.

“Occasionally partially mineralized in distal regions of the patagia, aktinofibrils were composite, helically-wound structures composed of much finer filaments a few microns in diameter.

“Comparable in size to aktinofibrils, but less common, are single-stranded, hair-like pycnofibers, seemingly branched in two specimens of the anurognathid Jeholopterus, that supposedly adorned parts of the cranium, neck, and body. Fiber-like structures have also been reported in cranial crests, foot webs, and tail flaps. The identity, homology, composition, and function of integumentary fibers is fiercely disputed.”

‘Fiercely’? Hyperbole. This issue was just raised by Unwin and Martill and I have yet to see their evidence. Here’s the evidence for pycnofibers on the fluffiest pterosaur of all, the owl-like holotype of Jeholopterus (Fig. 1) and a reconstruction of same (Fig. 2).

Figure 2. Wing and other extra dermal membranes surrounding Jeholopterus.

Figure 1. Wing and other extra dermal membranes surrounding Jeholopterus.

Figure 4. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

Figure 2. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

Unwin and Martill 2020 abstract continues:
“This study aimed to resolve these issues through analysis of 150+ specimens where the integument is preserved, representing >25% of known pterosaur species, 15 of the 20 principal lineages, and almost the entire temporal range of the clade. Details of the macro- and microstructure of fibers was obtained using light, UV and laser-UV photography, and binocular and scanning electron microscopy.”

Missing from their taxon list are any outgroups of the Pterosauria (Cosesaurus, Sharovipteryx and Longisquama, Fig. 3), all of which also have extradermal membranes and fibers, some of which form precursor wing fibers (Peters 2009).

Longisquama in situ. See if you can find the sternal complex, scapula and coracoid before looking at figure 2 where they are highlighted.

Figure 3. Longisquama in situ. See if you can find the sternal complex, scapula and coracoid before looking at figure 2 where they are highlighted.

Unwin and Martill 2020 abstract continues:
“Results of this study provide broad support for a new model in which pterosaur integumentary fibers of all types had a single common origin: dermal collagen. This idea is consistent with:

  1. exceptionally preserved examples of cranial crests, wing membranes, and integument associated with the neck and body, which demonstrate that fibers were embedded within the integument, and formed part of the dermis;
  2. calcification of fibers in the cranial crest and, occasionally, in distal parts of the flight patagia;
  3. the composite construction of fibers, which were composed of much finer, helically-wound fibrils.

There’s no argument there. Nothing fiercely disputed. Everyone agrees.

“Multiple specimens with soft tissues preserved in four different preservational modes, show that the integument had a glabrous, fine granular, or even polygonal external texture. Aktinofibrils and other collagenous dermal fibres (e.g., in cranial crests and skin associated with the neck and body) exposed by decay of the remarkably thin epidermis have frequently been misinterpreted as pycnofibers.”

The word ‘misinterpreted’ here should have been the leading sentence followed by evidence. Not the penultimate one followed by no evidence. Unwin and Martill should have taken the strongest evidence against their hypothesis and knocked it down with evidence. They had the opportunity, and they were paid to do this, but failed to do their job.

Figure 2. Here is the Vienna specimen of Pterodactylus in situ and with matrix removed. Now compare this figure with figure 3, which shows the wings and uropatagia unfolding. There is no way to turn this into a deep chord wing membrane. And it decouples the forelimbs from the hind limbs.

Figure 4. Here is the Vienna specimen of Pterodactylus in situ and with matrix removed. Where are the pycnofibers here? I see skin, but no fibers. Then again, the fluffiness of Jeholopterus gave it owl-like silent flight characteristics not needed in a beach combing wader.

Unwin and Martill 2020 abstract continues:
“External fibers fringing the jaws of anurognathids may be an exception, although branching, reported in one specimen, is likely an artifact of preservation.”

Only this one extremely minor exception? Let’s talk about the other major exceptions (Figs. 1, 2). And let’s talk about the lack of similar fibers on wading pterosaurs like Pterodactylus (Fig. 4). The fact that Unwin and Martill got the wing membranes wrong and continue to deny the lepidosaur ancestry of pterosaurs lead one to distrust and discredit everything else they say (= invalid phylogenetic context). And that’s something that should never happen to a couple of pterosaur experts.


References
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Unwin D and Martill D 2019. When the Mesozoic got ugly – naked, hairless, (and featherless) pterosaurs. SVPCA abstracts.
Unwin D and Martill D 2020. Identity, homology, and composition of fiber-like structures associated with the pterosaur integument. SVP abstracts 2020.

https://pterosaurheresies.wordpress.com/2019/10/02/unwin-and-martill-2019-find-pterosaurs-naked-and-ugly/

https://pterosaurheresies.wordpress.com/2020/09/30/naked-pterosaurs-or-feathered-phds-clash/

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