Pterosaur Flight: Koroljov 2017

Koroljov provides a hypothetical look
at how pterosaurs flew… evidently from an aerodynamic engineer’s point-of-view, and scores a zero by failing to strictly follow the data.

Unfortunately
Koroljov used outdated models for the wing membranes and uropatagia employing a deep chord wing membrane based on the invalidated Sordes model of Sharov (1971) and Unwin and Bakhurina (1994). He also proposes an ultra-deep chord membrane that would have a very hard time folding up (Fig. 1).

There is no indication
that Koroljov saw any actual specimens, and he overlooked or chose to ignore Peters (2002, 2009) and ReptileEvolution.com/pterosaurwings.htm which promotes the narrow-chord wing membrane both based on precise tracings of most known soft tissue pterosaur specimens. Koroljov also ignores the origin of pterosaur wings as documented here. Basically Koroljov referenced some past workers then added comments then suggested a few generalized mechanical drawings (sample Fig. 1).

Bogus Koroljov hypotheses include:

1. wing finger elongated to deal with ground effect – no, it was for thrust
2. pteroid homology with metacarpal 1 – no, the pteroid is a migrated centrale
3. wing finger is therefore digit 5 – no, all pertinent morphology debunks this.
4. imagines pre-wing ancestors – why imagine them when we have them?
5. hind limbs involved in wing membrane tension – no, the elbows were. The hind limbs were essentially decoupled, except for a fuselage fillet.
6. Pedal digit 5 involved in uroptagium tension – only in Sharovipteryx, which has dual uropatagia.
7. Posterior orientation of the hind limb in flight – no, it was lateral, like a horizontal stabilizer, or exceptionally as an inverted V, as in Dimorphodon, which had a right angle femoral head. Also lateral hind limbs in Sharovipteryx, which no one disputes.
8. Wing finger joints were prone to axial twisting – no, they were not, as fossils show.
9. “the flight finger was ventro- or dorsocaudally bent in the form of an arc rather than being stretched during flight” – no it was not, as articulated skeletons demonstrate
10. “The bird model of a pterosaur wing tacitly assumes…the flight finger and its turning with the dorsal side directed backward.” – this is madness! No one has ever promoted such a  bogus idea. The flight finger axially rotates with the dorsal side anterior or forward. Koroljov’s figure 4 shows his complete confusion when he illustrates that configuration, but places the three free fingers ventral on the palmar side of the wing finger rather than dorsal on the extensor side, changing the order of the fingers.
11. In tail vane pterosaurs, “the ‘flight control’ is focused at the end of the tail” – no, that’s a decorative element that passively serves to keep the tail aligned with the parasagittal plane, like arrow fletching.
12. Koroljov wonders how gigantic forms could have the same flight finger and wing membrane as in smaller tail-vane pterosaurs – not realizing that the very smallest pterosaurs were also of the pterodactyloid grade and had nearly identical shapes in every size in every detail as the giant ones, both phylogenetically and ontogenetically.
13. Hypertrophy of the caudofemoralis muscles on ‘advanced’ pterosaurs (his figure 17) – no, the tail is a vestige at that grade. The big pelvis anchors the femoral muscles.
14. Wing phalanx ratio differences “can be treated as an indirect proof of adaptation for… different methods of flapping flight” in rhamphs, but uniform in pterodactyloid-types – probably the LEAST IMPORTANT factor in their variation
15. Ventral deflection of the pelvis by 30º – no, except for coitus
16. “no definite answer concerning the foot position in flight” – no there is only one position, as anyone with a manipulable articulated skeleton can tell you.
17. “in basal pterosaurs, the foot was turned with the plantar surface directed downwards during flight,” – no medially. When the knees are extended laterally, the toes point laterally and the plantar surface is medial. Remember, Koroljov is still trying to incorporate pedal digit 5 into the uropatagium for his own imaginary reasons because no pterosaurs fossils document this – only Sharovipteryx. 
18. Pterodactyloids do not have a uropatagium – No pterosaurs have a uropatagium. But they all have slender uropatagia (plural).
19. Pterodactyloid-grade pterosaurs turn the plantar surface upward during flight – no, only when the knees are ventral to the pelvis, which is only during take off and landing.
20. the presence of a uropatagium is indicated by the elongated fifth toe – no, that would mean that Tanystropheus and Langobardisaurus also had a uropatagium, but they did not.
21. Anurognathids hunted in the narrow layer between water and fog at night, in no-wind conditions – gutsy call based on ground effect flying based on the short tail, similar to pterodactyloids. That may be too narrow of a niche in all respects.
22. Anurognathids were inverted clingers, based on uropatagia that, as in fruit bats, “protect the animal from rain during rest.” – another gutsy call considering that the femoral head was at a right angle to the femur in anurognathids, as in cursorial taxa, opposite to the bat femoral head.
23. Once the tail was shortened, it could not be newly elongated  – tell that to Zhenyuanopterus.
24. Dendrorhynchoides had only three phalanges in the flight finger – no, there were five (don’t forget the wingtip ungual!), as in all other pterosaurs.
25. Nemicolopterus is the smallest among pterosaurs – no, others were smaller.
26. “very small pterodactyloids were specialized in collecting arthropods from the skin surface of large dinosaurs.” – no, this was a role best suited to anurognathids.”
27. “Nemicolopterus is aerodynamically unique” – no, every hatchling of its size was similar. “unlikely to have had four phalanges” – no, if you look you can find all the standard phalanges. Bennett 1994 was wrong, too.
28. Beipiaopterus and Anurognathus also lose their fourth finger. – no, it’s present.
29. I’m only halfway through with the paper, but I’m going to quit here. You get the picture. I may critique the second half of the Koroljov paper later.

Koroljov does support these verified hypotheses and observations:

1. The close relationship of Sharovipteryx to pterosaurs
2. Ventral deflection of the wingtips achieved by flexion of the wing finger during certain phases of flight, especially during low, ground-effect flying, as in albatrosses
3. “very small pterodactyloids that could perform high-speed maneuvering flights” – yes, like hummingbirds and tiny bats.

Koroljov does not support a bird wing analogy,
but supports a bat wing analogy. Actually the best analogy for a pterosaur wing is a single primary feather, but one that can be folded to near invisibility when not in use. A lack of examination of the specimens, a lack of a phylogenetic framework, and a reliance on bad prior papers doomed Koroljov’s studies.

In his acknowledgements, Koroljov reports,
“The author is also grateful to A.N. Kuznetsov (Biological Faculty, Moscow State University) for his patience and attention that helped reduce the free flight of imagination to scientifically acceptable forms.” It is thus doubly strange that this paper by Koroljov came to my attention when Kuznetsov mailed Koroljov and myself both his paper and Peters 2002 with the note, “I dare to establish direct contact between you by attaching your articles on pterosaurs to this letter. Hope, this contact will help to inspire professional pterosaurology with new ideas.” 

References
Bennett SC  1994. Taxonomy and systematic of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea), Occas. Pap. Nat. Hist. Mus., 1994, vol. 169, pp. 1–70.
Koroljov AV 2017. The Flight of Pterosaurs.Biol Bull Rev 7: 179. doi:10.1134/S2079086417030045
Peters D 2000. 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 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Sharov AG 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 DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.