Unwin and Martill 2019 report:
“With key roles in flight, thermoregulation and protection of the body, the integument was of fundamental importance to pterosaurs. Determination of the basic anatomy of this structure could provide a range of new insights into the palaeobiology of these enigmatic volant reptiles. Presently, however, there are several conflicting hypotheses regarding the construction of the integument, all founded on limited numbers of specimens, and not one of which is fully consistent with the available fossil evidence.
As mentioned yesterday, pterosaurs are not enigmatic. Unwin and Martill have chosen to avoid the scaly lepidosaurian ancestors of pterosaurs cited by Peters (2000, 2007). The integument found on pterosaurs has similar precursor integument on sister fenestrasaurs like Sharovipteryx (Fig. 1) and Longisquama, adding two taxa to their short list of pterosaurs preserving scaly integument and pycnofibers exclusive of the extradermal membranes (wings and uropatagia).
Figure 1. Note the neck skin (integument) of Sharovipteryx, a pterosaur sister.
Unwin and Martill continue:
“We have developed a new model based on investigations of more than 100 specimens all of which show some form of exceptional preservation. This data set spans the entire temporal and systematic ranges of pterosaurs and a wide variety of preservational modes.”
So… “a limited number of specimens” (see above) just turned into “more than 100 specimens.” Did they just want to see if anyone was paying attention?
“The model has three principal components:
(1) A thin epidermal layer. The external surface of the integument was glabrous [= free from hair or down, smooth] with a smooth, slightly granular, or polygonal texture.
Attenuate ‘bristles’ fringed the jaws in two anurognathids and small tracts of filaments may have adorned the posterior cranium in some pterosaurs.
Perhaps these jaw and skull filaments should have been separately numbered because they are different than glabrous tissue.
(2) A layer of reticular and filamentous collagen and of variable thickness and complexity, formed much of the dermis.
Helically wound bundles of collagen fibres (aktinofibrils), were present throughout all flight patagia. Variation of aktinofibrils in terms of their dimensions, packing, orientation and stiffness permitted localized variation in the mechanical properties and behaviour of the flight patagia whichvaried from relatively stiff distally to more extensible and flexible proximally.
‘Feather-like’ structures reported in Jeholopterus appear to be partially unraveled or decayed aktinofibrils.
Again, these are all distinct tissues worthy of their own numbers.
Unwin and Martill have no idea that Jeholopterus was a vampire bat analog (Peters 2008) covered like no other pterosaur with fluffy, silent, owl-like extradermal integument. Neither Unwin nor Martill seem to make reconstructions, so neither has any idea what Jeholopterus looked like, unless they looked here (Fig. 2).
Finally, Unwin and Martill are mixing in flight membranes here. Perhaps THAT is where they get so many examples because otherwise dermal material is exceedingly rare. Integument generally means ‘covering’, so their inclusion of wing membranes is a little misleading, especially considering the ‘naked and hairless’ portion of their abstract headline.
Figure 2. Reconstruction of Jeholopterus. This owl-like bloodslurper was covered with super soft pycnofibers to make it a silent flyer.
Collagen fibre bundles were also present in footwebs, and in the integument of the neck and body. These structures have often been mis-identified as ‘hair’ (pycnofibres).
Again, this variety of tissues should have been numbered separately because they are different than tissue forming much of the dermis.
(3) A deep dermal layer with muscles fibres, blood vessels and nerves.
This variety of demal tissues were already described for the flight membranes, but it could also apply to normal tetrapod skin, like our own.
The pterosaur integument was profoundly different from that of birds and bats, further emphasizing the sharp disparity between these volant tetrapods.”
Why didn’t Unwin and Martill compare pterosaur integument to lepidosaur integument, specifically that of Sphenodon and Iguana (Fig. 3)? These are the two closest living relatives of pterosaurs in the large reptile tree. According to the LRT, Unwin and Martill are looking in the wrong places.
Figure 3. The dorsal and gular spines of Iguana are homologous with those in Sphenodon.
Not sure where Unwin and Martill
are getting data for pterosaur skin exclusive of the extradermal membranes. They don’t say. The dark wing Rhamphorhychus (Fig. 4) has the most incredible preservation of extradermal membranes, but the skull, neck and torso were prepared down to the bone.
Figure 4. The darkwing specimen of Rhamphorhynchus. Top: in situ. Middle: Soft tissues highlighted. Bottom: Neck and forelimb restored.
So, why do Unwin and Martill think the Mesozoic got ugly?
Their abstract does not seem to answer their click-bait headline, which describes naked, hairless and featherless pterosaurs without giving one example of same based on evidence. On the contrary, employing phylogenetic bracketing, between Sharovipteryx (Fig. 1), Scaphognathus and Sordes (the hairy devil, Fig. 5), basal pterosaurs were not naked. Their fibers were not the same as hair or feathers, but unique to fenestrasaurs.
Figure 5. The hind limbs and soft tissues of Sordes. Above, color-coded areas. Below the insitu fossil.
Why were pterosaurs considered naked by Unwin and Martill when hairy Sordes (Fig. 5) was studied by Unwin, known to Martill, and not mentioned in the abstract? Very strange, indeed coming from these two.
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 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Unwin D and Martill D 2019. When the Mesozoic got ugly – naked, hairless, (and featherless) pterosaurs. SVPCA abstracts.