Have you heard the tragedy of rounded wingtips the wise?

Recently a controversy (which I’m using the broadest definition of the term since this hasn’t actually caused any significant drama) revolving around the maxim that pterosaurs have rounded wingtips has erupted on twitter. World renowed paleontologist and actually-legitimate cryptozoologist Darren Naish has noted that there has been an emphasis on “rounded wingtips” when describing and depicting pterosaur wings in modern paleoart; upon a response from Dave Hone (whoch has published the paper responsible for this) this has evolved in a broader conversation about wing membrane lobes and the actual shape of the pterosaurian distal phalange.

TL;DR: pterosaur wing tips were rounded to some extent… but also not.

What is “pointy” actually?

Examples of alleged modern pointy wings, a frigatebird (putneymark) and a Mexican free tailed bat (jabz photography). Note that in both cases the sharpness of the wing is undermined by different segments (feathers and cheiropatagia respectively) that still blunt the terminal profile. Pterosaur aktinofibrils apparently did the same.

First of all, lets get a few things straight:

  • The Dave Hone paper linked above that started this whole thing doesn’t explicitly make a pointed wing an impossibility, just unstable and stupid. Natural selection doesn’t operate on intentional perfection, so a “subpar” design can still exist if it doesn’t flat out damage an animal’s survival. Thus, a pterosaur with pointy wings could hypothetically still fly, just not as well as one with a stable rounded wingtip.
  • That said, there is evidence that most pterosaurs had terminal phalanges that were curved to some degree, so this selective pressure is evident on the fossil reccord, though not universal (see below).
  • Darren Naish doesn’t dispute the presence of some roundness (though he clearly favours a minimalistic take on that). What he is mostly concerned with is what he calls a “convex lobe”, a section of the membrane projected that blunts the wing shape.

With that out of the way, we are left with two main issues:

  • Are pterosaur wings universally blunt? Or are there exceptions?
  • Was there evidence of a lobe?

The former is already semi-addressed: most pterosaur wings have curved end phalanges, as the paper demonstrates. HOWEVER, this actually doesn’t seem to be universal: in rhamphorhynchids at least, the terminal wing phalanges seem to be pointy, and in the case of Bellubrunnus they actually do the opposite of most pterosaur phalanges and curve outwards.

So yes, for whatever reason rhamphorhynchids and a few other groups gave this trend the wingfinger. However, they are the exception that proves the rule, as they are considered aberrant for this.

Onto the next point, the presence of a lobe. I think we can safely argue against the massive lobes seen in some diagrams like the article opener, but Darren Naish actually argues against even small lobes like in this reconstruction of Bellubrunnus:

This I have to disagree with. Abundant studies have some that the distal section of the wing membrane of pterosaurs was full of rigid aktinofibrils (Witton 2013, th aofrementioned Dave Hone paper), so it was clearly an adaptation to generate a more rigid membrane in this area. While this does not prove the existence of a large lobe, it does make the existence of a small degree of convexity, certainly enough to at least smoothen the terminal wing in conjunction with the curved phalanges.

Along the way some people on twitter used examples of alleged pointy wings in modern animals like some seabirds and bats. However, in both cases the “sharpness” of the wing is severely undermined:

  • In most birds, flight feathers have round distal margins. Additionally, they form the wing in multiple segments; if one feather is damaged, others can make up for it. They certainly did not have a bony element sticking out as in the “pointy pterosaur wing” model. In fact, I find pictures of birds with fully sharp wings to be fairly rare, with even triangular winged species like falcons and frigatebirds usually having splayed feathers at some point in their flight cycle.
  • In bats, the wing is inherently rounded due to the presence of multiple wing fingers. Sharp wing fingers are by themselves rather rare in healthy specimens — they’re emmersed in membrane, hence why they lost their claws — at most you have species where the third finger is particularly elongated as to form a subtriangular wing. Like pterosaurs they have specialised fibers (in their case muscle groups) that prevent fluttering and maintaing the membrane’s shape in flight.

So yes, I think pointy wings are biologically inaccurate and evidence points towards at least somewhat round wing tips. But not too round, as large convex lobes are absent.

Prehistoric Planet

Prehistoric Planet azhdarchid model. Since this is a teaser picture I’m assuming it is okay to use.

This controversy has come just in time for Prehistoric Planet’s release, easily the most spectacular prehistoric documentary to date. Since Darren Naish and Mark Witton had creative control on pterosaur wings, how do they fare?

In pteranodontians, they are in fact rounded. Not too rounded, but a combination of curved phalanges and some soft tissue trailing make them more in line with the modern paleoart trend.

Azhdarchids, on the other hand, have extremely pointy wings. This makes less sense to me because they were inland flyers, which tend to have broader wings, though their distal phalange curvature is less pronounced so a large convex lobe would be necessary to create their rounded wingshape.

Overall I’m satisfied with the results, but I hope the discussion continues, especially since some people are naturally being imbeciles and going the opposite direction.

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