Can volant fossil vertebrates inspire mechanical design?

Martin-Silverstone, Habib and Hone 2020 review volant fossil taxa,
in their hope to “synthesise key elements to provide an overview of those cases where fossil flyers might provide new insights for applied sciences.”

Caveat
readers should note, these authors have been responsible for some of the current pterosaur myth-making (e.g. pterosaur quadrupedal catapult launch) in the academic literature. (To see the entire list, enter the keywords “Silverstone”, “Habib” or “Hone” in the white box above).

Even so, let’s start with a fresh slate
and see what they have to say.

The authors report,
“Soaring is a form of passive flight (though as with gliding, is often a behaviour of powered fliers) which involves using external sources of lift.”

“Change ‘often’ to ‘always’. Soaring only comes to those who have excelled at powered flight earlier. Soaring is the next step for the highest, longest-range flyers.

“Unique fossil-only bauplans have also been described, such as the nonavialan dinosaurs Yi qi and Ambopteryx.” 

Not unique. Misinterpreted, as detailed here. Both Yi qi and Ambopteryx are derived from specific Late Jurassic Solnhofen birds (specimens traditionally assigned to Archaeopteryx), in the large reptile tree (LRT, 1663+ taxa) which makes them avialan dinosaurs. The proper phylogenetic context must be the foundation.

On the same subject, later in their text, “the recently discovered Yi and Ambopteryx show a melange of features – notably an enlarged wrist bone supporting an apparently small membranous wing, but also a flight surface composed of feathers.” This is a myth. That ‘wrist bone’ is either a radius or an ulna, depending on which wing is under consideration as corrected and detailed here.

Figure 1. Above: freehand image from Martin-Silverstone 2020 of Quetzalcoatlus northropi wing. Pink arrows call out errors. Below: Traced image of Q. sp. wing.

Figure 1. Above: freehand image from Martin-Silverstone 2020 of Quetzalcoatlus northropi wing (based on the humerus shape). Pink arrows call out errors. Below: Traced image of Q. sp. wing after firsthand examination in the Wann Langston lab where the fossils were kept years ago.

Credit where due:
In the authors’ illustration of the pterosaur wing (Fig. 1), they correctly located the pteroid on the radiale, but incorrectly placed the medial carpal there, too. Free fingers 1–3 are too large and appear to be on top of one another, with their palmar surfaces facing anteriorly, following Bennett (2008, Fig. 2). In reality the palmar surfaces faced ventrally in flight with only metatarsal 3 attached to the wing finger, as in all other tetrapods (Fig. 2). That makes the free fingers point laterally while quadurpedal, as ichnites show. The wing membrane illustration (above) mistakenly extends to the hind limbs. This is the myth of the bat-wing pterosaur promoted by several Bristol professors.

Ironically,
the authors chose a flightless pterosaur, Quetzalcoatlus, to model their volant wing.

Pterosaur hand dorsal view

Figure 2. Pterosaur hands, dorsal view, the two opposing hypotheses.

Continuing onward to the bottom of their Figure 1
(Fig. 3 below), the authors mislabeled the left and right wings in this dorsal view (with scapulae indicating the dorsal side) of the BSP 1937 I 18 specimen of Pterodactylus.

Figure 2. This is Figure 1B of Martin-Silverstone et al. 2020 where they mislabel the left and right wings of BSP 1937 I 18. Colors added to show the extent of the wing membrane. See figure 4 for an animation of a similar fossil.

Figure 2. This is Figure 1B of Martin-Silverstone et al. 2020 where they mislabel the left and right wings of BSP 1937 I 18. The authors labeled this specimen “Aerodactylus”, but it nests in the midst of several Pterodactylus specimen.  Colors added to show the extent of the wing membrane. See figure 4 for an animation of a similar fossil. I did not color the uropatagia behind each knee. You can see those plainly here.

The lower arrow pointing to the ‘membrane’
(‘m‘ in Fig. 2) just barely points to the trailing edge of the membrane, just missing the space behind the elbow, where, as Peters (2002) showed (and see Fig. 4) the wing membrane stretched only between the elbow and wing tip, contra Martin-Silverstone, et al. (Fig. 1). The upper arrow points to the biceps (light red), not the propatagium membrane (yellow).

Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

Figure 4. This is the Vienna specimen of Pterodactylus, which preserves soft tissue membranes as in Fig. 3.

The authors labeled the BSP 1937 I 18 pterosaur, ‘Aerodactylus‘.
According to Wikipedia, “Aerodactylus is a dubious pterosaur genus containing a single species, Aerodactylus scolopaciceps, previously regarded as a species of Pterodactylus.”

In the large pterosaur tree (LPT) the BSP 1937 I 18 specimen nests between several other Pterodactylus specimens.

The authors report, 
“It is therefore the evolution of more extreme vane asymmetry, rather than slight asymmetry, that was critical to avian flight.”

According to the LRT, it is the elongation of locked down corticoids (and the clavicle in bats because they lack a coracoid) marks the genesis of flapping, which is more critical to avian flight.

The authors report, 
“The largest pterosaurs reached in excess of 10 m in wingspan, 250 kg in weight, and had skulls perhaps 3 m long, vastly exceeding any other known flying animal in size and weight.”

Actually the largest pterosaurs, like the largest birds, were flightless, as shown earlier here.

With regard to pterosaur wing membranes, the authors report, 
“All fossils that have relevant portions preserved and undistorted show the membrane attaching to the lower leg or ankle.” 

Actually, none of them do, including their Figure 1 (Fig. 2 above). The authors referenced Elgin, Hone and Frey 2011, another botched paper discussed earlier here. You might remember, the authors employed a fictional “shrinkage” to explain away all the fossils that did no fit their preconception, but all matched the observations in Peters 2002.

The authors report,
“Mechanical considerations indicate that pterosaur wings must have had a concave posterior margin to avoid aeroelastic instability.”

Why guess, hope and assume when you can observe? The aktinofibrils are there to avoid aeroelastic instability.

The authors report, 
“Proper tensioning of membrane wings in pterosaurs would have been impossible with a convex posterior margin, because of the single-spar construction.”

Tension between the elbow and wing tip (Peters 2002) is supported by fossil evidence (Figs. 2, 3).

The authors report,
“It has been suggested that the largest pterosaurs were secondarily flightless, but more recent work suggests that the maximum launch-capable body mass for pterosaurs may have been high, owing to the high maximum lift coefficient of their wings and their potential for quadrupedal launch.”

This is Habib’s claim based on imagined and falsified ‘evidence’ argued here. Habib’s hypothesis was based on an imagined elastic catapult potential in the wing knuckle pressed against the ground, but pterosaurs never do this according to track evidence. Click here to see the doctored evidence presented by Habib 2008.

The authors also cite the PhD thesis of C. Palmer, University of Bristol 2016. One of his first assignments as a PhD (October 2016 ) must have been to place an seeking a student, to investigate the effectiveness of the quadrupedal launch [of pterosaurs] and by comparing it with the bipedal launch of birds, test if it was one of the factors that enabled pterosaurs to become much larger than any bird, extant or extinct.” You can read more about that advert here.

Wait a minute… since that quad launch hypothesis was a subject in Palmer’s PhD dissertation (according to the Martin-Silverstone, et al. citation, why was he advertising for someone else with less experience to take on this task? Let’s remember, students and PhD candidates have the least experience in the field. Most of the myth-making in pterosaurs comes out of universities in Southern England, evidently where students have to produce what their professors demand, or fail.

Please note: In the advert the Bristol bunch were not testing the hypothetical quad launch of pteros against the hypothetical bipedal launch of pteros. For them, quad launch was/is ‘a given’ that must be proved, despite the danger to the pterosaur, the criticism from colleagues and the lack of evidence.

At this point,
I’m only halfway through the paper. The rest we’ll save for later, if necessary. For now, some concluding remarks.

The authors stated their goal in lofty language, 
“A robust understanding of the origin of flight and the evolution of morphologies related to flight performance provides critical context for the constraints and optimisation of biological traits that can inspire mechanical design.”

The problem is, the authors have collected and presented invalid data. They have avoided putting the origin of bats, birds and pterosaurs into their proper phylogenetic context by showing the origin of flapping. How can the authors hope to emulate a pterosaur mechanically if they are freehand designing their own fictional pterosaur (Fig.1) and not looking carefully at specimens under their nose (Fig.2)? A scientist should always be trying to falsify a claim. I don’t see that here. By ignoring the literature (and the evidence) that falsifies a claim, these three authors are not acting like scientists.

With regard to mechanical pterosaurs,
the Stanford pterosaur project did not fair as well as simpler ornithopter designs.

The famous MacCready mechanical flying pterosaur
(Figs. 5, 6), was ostensibly modeled on the smaller Quetzalcoatlus specimen (Figs. 5, 6), but MacCready extended the wingspan to make his model fly. For a discussion on mechanical pterosaurs, it’s a little strange that the keyword, “MacCready” yields no results in their PDF.

Figure 5. The Macready flying model compared to Q. sp. Perhaps it has always been overlooked that the neck proportions were changed and heavy mechanical motors and batteries filled the torso.

Figure 5. The Macready flying model compared to Q. sp. Perhaps it has always been overlooked that the neck proportions were changed, even though the body included the weight of the motor, batteries, radio and controls. The wingspan is longer on the flying model than on the real genus.

We looked at arguments against
the hypothesis of giant volant pterosaurs here. The first thing that pterosaurs do when they give up flying is to shorten the distal wing phalanges, a fact overlooked by Martin-Silverstone, Habib and Hone. The keyword, “vestigial” does not appear in their PDF. The keyword, “distal” appears, but not in regards to pterosaur wing phalanges.

Figure 6. Paul MacCready's flying pterosaur model had longer wings than Q. sp., with its vestigial distal wing phalanges. Here the model and its inspiration are shown to the same length.

Figure 6. Paul MacCready’s flying pterosaur model had longer wings than Q. sp., with its vestigial distal wing phalanges. Here the model and its inspiration are shown to the same length.

Once again, and true to Professor Bennett’s curse,
“You will not be published, and if you are published, you will not be cited,” my published papers on the origin of pterosaurs from fenestrasaurs (Peters 2000), the origin and shape of pterosaur wings (Peters 2002), and the origin and orientation of the pteroid (Peters 2009) were not cited by these authors. As good scientists they should have cited these papers, discussed the presented data, constructed arguments, and most importantly, attempted to falsify their own hypotheses with faithful and precise observations unsullied by invented excuses (‘shrinkage’). Only when they get their pterosaurs right will they have a good basis for discussing mechanical equivalents. And please cite the work of inventor Paul MacCready.

PS
Citation #76 in Martin-Siverstone, et al. (Zakaria et al. 20160 discusses several mechanical aspects of pterosaurs. They copied the bad pterosaur bauplan from Elgin, Hone and Frey 2011 (Fig. 7) then provided an optimized wing plan with a narrower chord from their studies (Fig. 8) that more closely matched the actual wing shape of pterosaurs in Peters (2002).

Problems with the Elgin, Hone and Frey (2011) pterosaur wing model with corrections proposed by Peters (2002).

Figure 7. Above problems with the Elgin, Hone and Frey (2011) pterosaur wing model with corrections proposed by Peters (2002).

All I can say is,
it’s a topsy-turvy world out there where bad data rules the day.

Figure 8. When Zanzaria et al. 2016 used math to model the optimum pterosaur wing, they found a narrow chord, as in figure 7, worked better.

Figure 8. When Zanzaria et al. 2016 used math to model the optimum pterosaur wing, they found a narrow chord (red), as in figure 7, worked better than the ‘actual shape’ actually invented by Elgin, Hone and Frey 2011 wing (black).

Added a few days later:
From the Scientific American article that promoted four-fingered tenrec tracks as Crayssac pterosaur tracks: “Elizabeth Martin-Silverstone, a pterosaur expert at the University of Bristol in England, who did not take part in the work, says the fossil is the ‘final nail in the coffin of the idea that basal pterosaurs were awkward and clumsily walking around—and definitely of the idea that early pterosaurs might have been bipedal.” Not only did they walk on all fours, “but they moved around quickly and with style,’ she adds.” Martin-Silverstone is not using critical thinking. Four fingers and anteriorly-oriented manus tracks invalidated these as possible pterosaur tracks. Many pterosaurs and their fenestrasaur tritosaur lepidosaur ancestors were bipeds. See keyword “Rotodactylus” in the white box above.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Habib M 2008. Comparative evidence for quadrupedal launch in pterosaurs. Pp. 161-168 in Buffetaut E, and DWE Hone, eds. Wellnhofer Pterosaur Meeting: Zitteliana B28
Mazin J-M, Billon-Bruyat J-P and Padian K 2009. First record of a pterosaur landing trackway. Proceedings of the Royal Society B doi: 10.1098/rspb.2009.1161 online paper
Martin-Silverstone E, Habib MB and Hone DWE 2020. Volant fossil vertebrates: Potential for bio(-)inspired flight technology. Trends in Ecology & Evolution (advance online publication) doi: https://doi.org/10.1016/j.tree.2020.03.005
https://www.sciencedirect.com/science/article/abs/pii/S016953472030080X
Palmer C 2011. Flight in slowmotion: aerodynamics of the pterosaur wing. Proc. R. Soc. Lond. B Biol. Sci. 278, 1881–1885.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Prondvai E and Hone DWE 2009. New models for the wing extension in pterosaurs. Historical Biology DOI: 10.1080/08912960902859334
Sharov AG 1971. New flying reptiles fro the Mesozoic of Kazakhstan and Kirghizia. Trudy of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Zakaria MY. et al. 2016. Design optimization of flapping ornithopters: the pterosaur replica in forward flight. J. Aircraft 53: 48–59
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

http://reptileevolution.com/pterosaur-wings.htm
http://reptileevolution.com/pterosaur-wings2.htm

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