Behind the Scenes at the AMNH pterosaur exhibit

Here‘s a NY Times article about the new AMNH pterosaur exhibit. We looked at the AMNH pterosaur exhibit website earlier here. The online article url was sent to me by “I love pterosaurs” who wants me to “Please, learn how real scientist work.” [sic]

Okay, let’s see how real scientists work.
The following is from the online article (unfortunately, only a fraction focused on the pterosaurs and their artistic creation):

“Most of the questions that we actually get from artists, the answer is, ‘I don’t know,’” Dr. Kellner said. But the more research that’s done, the closer their guess can be on an animal that’s been extinct for 66 million years.

“In art you can do whatever you want,” Dr. Kellner said. “You have an expression of how you feel about a certain subject. But in paleo art, you don’t have that liberty. You must try to present the reconstruction of those animals the best way that you can based on true scientific evidence.”

“Sometimes, changes in science happen so quickly that an artist’s creation must be considerably altered. The feet of Quetzalcoatlus underwent major changes as well: Five toes per foot were edited down to four; they were shortened and the toenails removed.”

Sounds like the artists are getting good advice “based on scientific evidence” from the curators, but then…

Good gravy!
I haven’t seen any pterosaurs with four toes. There’s always a vestige to #5. And if these are the toes (they’re big ones, Fig. 1) the AMNH is advertising their inaccuracies early. Someone must have been influenced by theropods here (Fig. 1) because azhdarchid toes don’t go short on number 1.

Figure 1. Based on their size, these must be the Quetzalcoatlus feet and hands. I’ve added some real azhdarchid feet and ichnites here. Metatarsals should be appressed to match the fossils and tracks. All four medial metatarsals should be subequal. Claws should not be so thck. Remember the bones are more like soda straws than robust dino feet. It’s too bad no one looked at the data here.

Azhdarchid feet were narrow, with appressed metatarsals, as their fossils and ichnites show (Fig. 1). The evidence does not support these feet.

However
Not all giant pterosaurs were azhdarchids. Earlier we looked at some wider giant bipedal Korean pterosaur tracks here, likely made my tapejarids or shenzhoupterids with webbed feet, as shown in the AMNH feet (Fig. 1) . Even so four long metatarsals and toes is the rule. If the above pterosaur made tracks they would be mistaken for theropod tracks.

Figure 2. Basic errors in the big Quetzalcoatlus model. The short wings and ultra size give away the genus.

Damn, I hate to see this.
I know those artists are working hard to get things as accurate as possible. So don’t blame them. They’re only taking orders.

On the good side:
The color, texture and size of the model pterosaurs is great. And so is their presentation. I just think they missed the excitement of pterosaurs the way the fossils reveal them to be.

And that’s the reason behind this blog. It’s a crusade for scientific accuracy supported by evidence.

Figure 3. Quetzalcoatlus in dorsal view, flight configuration based on bones from Q sp.  and wing membranes form other pteros.

Pterosaurs were unlikely floaters: Hone and Henderson (2013, 2014)

Recently Hone and Henderson (2013) conducted computational experiments with four digital pterosaur models (Fig. 1) and report, “we show that the floating posture of pterodactyloid pterosaurs led to the head, neck and body being horizontal with the ventral 1/4 to 1/3 being immersed, and the external nares being almost at, or potentially partially below, the waterline that could have left them vulnerable to drowning. These results suggest many did not regularly rest on the surface of the water and if immersed would need to take off again rapidly. The high numbers of fossils of juvenile pterosaurs compared to the terrestrial Mesozoic dinosaurs suggests that this may be linked to their poor ability in water.”

Obviously they thought they were professing pterosaur heresy, since so many illustrations from several sources imagine pterosaurs floating (Wellnhofer 1991, p.169; Lockley and Wright 2010, p. 73). According to Hone and Henderson (2013, Fig. 1), if pterosaurs floated at all, it was not too well and not for long.

They briefly mentioned traces of the pedal claws only, which were widely considered to be made by floating, paddling pterosaurs. They completely ignored all reports of manus only traces, like those here. Their colleague Mark Witton writes in pterosaur.net, “Wading behaviour may also be recorded: bizarre pterosaur trackways comprised of manus prints alone have been suggested to be created by pterosaurs wading in shallow water with buoyed-up hindquarters.” Manus only tracks were reported by Parker and Basley (1989), Lockley et al. (1995), Pascaul Arribas and Sanz Pérez (2000).

Here (Fig. 1) are models by Hone and Henderson for Rhamphorhynchus and Pteranodon, two taxa known to be fish eaters and therefore likely floaters. Note the effort needed to raise the skull out of the water in these stiff-neck models. Also note the too-slender forelimbs and too-slender thighs. Compare these to figures 2-5, based on bones.

Figure 1. Computational models of two pterosaurs from Hone and Henderson 2013. Note how both models have trouble keeping their nose out of the water, as they report. Neither of these models has a robust thigh typical of most pterosaurs. Also missing here in Rhamphorhynchus is a deep posterior abdomen caused by the deep prepubis.

Not considered here:
Hone and Henderson also modeled Dimorphodon, a basal pterosaur that likely was an insectivore, since all  sister taxa are also considered insect eaters. The Dimorphodon skull is a fragile wonder, so it was an unlikely fish-eater and therefore an unlikely candidate as a floater. Hone and Henderson also modeled Dsungaripterus, a stork-like wader. With such unique crushing teeth, it is not known what it preferred in its diet, but waders, like storks, are typically not floaters. I can’t find a single image of a floating stork on the Internet.

Mathematically manipulating their models, Hone and Henderson dialed up and dialed down various factors, such as density, placement of the lungs, etc. Reportedly, these did little to change the results of the apparently top-heavy, skull-leveraged pterosaurs.

The one thing they did not attempt
was to loosen the shoulder joints, which allows the pontoon-like forelimbs to float horizontally while the torso rotates between them. Their digital models also fail to accurately echo living tissue (described below and in later posts).

Figure 2. Floating pterosaurs from ReptileEvolution.com showing the large solid thighs, that counterbalance the air-filled skull. Like birds, the neck is able to raise the skull above the surface. Note how the forelimb pontoons are able to rotate, which elevates or depresses the torso. Ctenochasma (above) is ‘poling’ on its forelimbs, matching manus-only pterosaur tracks that were mentioned by Hone and Henderson, but can only be made by floating

Birds keep their wings out of the water. Bird wings are not flotation devices.

On the other hand,
pterosaurs come with their own rotating pontoons. So they can change the configuration of the body and the elevation of their skull relative to the water surface all sorts of ways, a point overlooked by Hone and Henderson’s static models.

Figure 3. Triebold Pteranodon in floating configuration. Center of balance marked by cross-hairs. Note the forelimb pontoons, submerged here.

I think Hone and Henderson underestimated the ability of large hollow, air-filled wings to float their owners. They underestimated the mass of the large and muscular thighs, perhaps the largest muscles in the body, to possibly depress the rear end. They also underestimated the ability of the cervicals to dorsiflex and they did not understand the ball joint at the back of the skull that allowed the neck to diverge at a large angle.

Figure 4. Two configurations for Rhamphorhynchus. Because the wings act like pontoons, the torso and skull can be rotated relative to the wings to adopt a variety of floating configurations. Also note the large webbed feet, preserved in the darkling specimen. The tail can be elevated at its base. Here the deep prepubis creates a deep abdominal keel not reflected in the Hone and Henderson digital model.

Imagine flocks of Rhamphorhychus enjoying the tidal pool like a bunch of kids with their “floaties” in a pool. Large webbed feet could have been used to paddle around or help launch this pterosaur by rocketing it out of the water along with several big wing flaps. We looked at this topic earlier here and here.

Figure 5. The derived Nyctosaurus, KJ2 in a floating configuration using its long forelimbs as pontoons.

Even the large crested Nyctosaurus can ride the waves with its “mast” over the center of gravity and the center of balance, the shoulder joint (Fig. 5).

Too much water on the wings?
While Hone and Henderson (2013, Fig. 1) do not show wing membranes, Henderson (2010) does and they are all bat-like with a very deep chord extending to the ankle. No wonder Hone and Henderson (2013) thought the weight of water on such an extended membrane might give the pterosaur trouble lifting its wings above the surface once dunked.

Unfortunately,
this is one more error to add to their pile. First of all, the wing was much narrower than Hone and Henderson suppose. Then, when pterosaurs folded their narrow wings, the membranes folded down to almost nothing. This is shown in several fossils, but cannot happen if the wing has a deep chord and attaches to the thigh or ankle. Finally, if the wings had a water-shedding surface, like that of diving birds, or that little floating lizard (Fig. 6), then what little water was present, would fall off rapidly.

Figure 6. Images of floating lizards. The small one in the middle, like tiny pterosaurs, takes advantage of surface tension to ride high and dry while spread-eagle on the surface.

Tiny pterosaurs: not all juveniles
Seems Hone and Henderson are still stuck in the ptero dark ages thinking tiny pterosaurs were all juveniles. They’re not, according to phylogenetic analysis and the fact that pterosaurs matured isometrically. In any case, as the small lizard shows (Fig. 6), tiny pterosaurs were more likely to float than large ones, based on surface tension and their tiny mass. Tiny pterosaurs had more surface area than any nonviolent lizard. So they would have been great floaters. And…need I say it? Pterosaurs are lizards.

I’ve never been a fan
of Henderson’s models. I think he disfigures pterosaurs. I’ve never been a fan of Hone’s work, either. I think he’s taken us several steps backward in our understanding of pterosaurs. (Use keyword “Hone” in this blog to find other examples.)

More on this tomorrow and the next day where we’ll match manus only tracks to trackmakers and take another look at digital models.

References
Hone DWE, Henderson DM 2013. The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats, Palaeogeography, Palaeoclimatology, Palaeoecology (2013 accepted manuscript), doi: 10.1016/j.palaeo.2013.11.022

Hone DWE, Henderson DM 2014. The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats. Palaeogeography, Palaeoclimatology, Palaeoecology 394:89–98.
Lockley MG, Logue TJ, Moratalla JJ, Hunt AP, Schultz RJ and Robinson JW 1995.  The fossil trackway Pteraichnus is pterosaurian, not crocodilian: implications for the global distribution of pterosaur tracks. Ichnos, 4: 7–20.
Lockley M, Harris JD and Mitchell L 2008. A global overview of pterosaur ichnology: tracksite distribution in space and time. Zitteliana B28: 185-198.pdf
Mickelson DL, Lockley MG, Bishop J, Kirkland J 2004. A New Pterosaur Tracksite from the Jurassic Summerville Formation, Near Ferron, Utah. Ichnos, 11:125–142, 2004
Parker L and Balsley J 1989. Coal mines as localities for studying trace fossils. In: Gillette DD and Lockley MG (Eds), Dinosaur Tracks and Traces; Cambridge (Cambridge University Press), 353–359.
Pascual Arribas C and Sanz Perez E 2000. Huellas de pterosaurios en el groupo Oncala (Soria España). Pteraichnus palaciei-saenzi, nov. ichnosp.  Estudios Geologicos, 56: 73–100.

New bat take-off video employs a minor ‘second stage’ boost

A recently posted bat take-off video documents how a tiny bat (not a vampire) does a magnificent pushup, reaches the acme of its trajectory then produces its first flap. Bat take-off has been used as an analogy for pterosaur take-off. But this bat comes with a difference.

Figure 1. Bat takeoff video. Click to view. Note the wing tips providing “second stage” thrust. The big question is could any flying animal larger than this bat launch in a similar fashion? The other big question is, did pterosaurs use their wing tips to provide “second stage” thrust? The current pterosaur forelimb hypothesis does not include wing tip thrust in that scenario.

This video comes with a difference.
This bat goes belly down to ‘cock’ the launch and it is also using its finger/wing tip to assist the launch by providing “second stage” thrust. The wing tip is the last part of the bat to leave the ground.

This differs from hypothetical pterosaur launches
in that most pterosaurs would be unable to ‘belly down’ due to limb proportions. And current forelimb launch hypotheses do not involve the extension of the wing finger to providing additional thrust for the initial leap.

In bats extending that wing finger during the initial phases of that leap also prepare the wing for that initial down flap. In pterosaurs the complete extension of the wing during that initial leap not happening fast enough is one of the main problems with the forelimb launch hypothesis. The other problem is most pterosaurs were overall larger-to-incredibly-larger than the bat in the above video. Doubling the height cubes the weight. That’s why giraffes don’t leap like gazelles despite their similar proportions.

We still have no launch tracks, fore or hind
So the fore limb launch for pterosaurs remains hypothetical. For that matter, so does the hind limb launch hypothesis. But if pterosaurs did launch with their fore limbs, then they might as well act like bats and use those big wing fingers to not only provide additional “second-stage” thrust, but to deploy those big wings prior to the acme of the launch trajectory. Now, whether or not pterosaur wings could do this is yet to be resolved.

And maybe only those pterosaurs the size of the bat above were capable of such launches. Mass matters.

Reinterpreting pterosaur wings – svp abstracts 2013

Figure 1. The Vienna Pterodactylus. Click to animate. Wing membranes in situ (when folded) then animated to extend them. Bennett 2013 confirms this wing morphology, previously and mistakenly attributed to “membrane shrinkage” by Elgin, Hone and Frey 2011 . The static images are from Peters 2002.

From the abstract
Bennett 2013 wrote: “The Vienna specimen of Pterodactylus antiquus (Natural History Museum, Vienna specimen NHMW 1975/1756/0000) is complete, fully articulated, and preserves propatagial and brachiopatagial soft tissues on part and counterpart slabs. When first described, linear features in the patagia were interpreted as widely spaced cylindrical internal elastic actinofibrils present throughout the brachiopatagium, a projection into the suboval window framed by trailing edge behind the right elbow was interpreted as the result of bunching of actinofibrils originating at the carpus, and it was suggested that the appearance that the brachiopatagium attached to the distal femur might be misleading because Desmodus can present a similar appearance with wings folded at rest. The recent discovery of closely spaced broad flat keratinous actinofibrils and distinct fold lines in the wings of Rhamphorhynchus muensteri (e.g., Zittel wing, Marsh specimen) prompted a reevaluation of the Vienna specimen. It was found that linear features in the patagia include: 1) closely spaced broad flat structures subparallel to wing phalanges, lightly permineralized with calcite on the upper slab, interpreted as keratinous actinofibrils of folded dactylopatagium; 2) clumped straight structures originating behind the metacarpophalangeal joint and resisting longitudinal compression to project into the window on the right and a like distance behind the elbow on the left, interpreted as actinofibrils associated with fold A; and 3) often curving structures that parallel the leading edge of the propatagium and the trailing edge of the brachiopatagium medial to the window, interpreted as collagen fibers bearing tensile loads in tenopatagial patagia. The suggestions as to the appearance of trailing edge attachment to the thigh is accepted. The absence of uropatagial impressions indicates they were less resistant to decay than propatagia and plagiopatagia, probably because their tensile fibers were smaller and/or fewer. The new information permits a new reconstruction of Pterodactylus wings.”

Notes
Nice to get confirmation of the narrow chord wing membrane reconstruction with a fuselage fillet extending to the anterior thigh. As reported earlier, Peters (2002) followed Schaller (1985) and Zittel (1882) in presenting this interpretation and configuration as the ONLY true pterosaur wing membrane configuration — found in every known specimen, no exceptions.

Earlier we looked at Bennett’s reinterpretation of aktinofibrils as much wider structures. Now that they have been observed in two specimens the validity is enhanced. Even so, I would like to see an independent researcher confirm the observation. I’m still concerned about the “inextensibility” that Bennett mentioned, as the Vienna specimen shows how extensible the wings can be.

Surprised to see that Bennett thought the uropatagia were absent. Here’s a photo in visible light. Be sure to mouse over to see the interpretation of the outline. Below (Fig. 2) is another photo in visible light. A photo in UV light (Fig. 3) where the uropatagia appear to be missing because they don’t glow, but did leave boundary lines, just like the right propatagium.

Figure 3. The Vienna specimen in visible light. The uropatagia are indeed ephemeral.

Figure 2. From Witton (2013) the Vienna specimen of Pterodactylus with a beautifully preserved wing membrane that is shallow at the elbow, stretched between the wingtip and elbow and includes a small fuselage fillet back to mid thigh. The uropatagia do not glow here.

References
Bennett S 2013. Reinterpretation of the wings of Pterodactylus antiquus based on the Vienna specimen. Journal of Vertebrate Paleontolgy abstracts 2013.
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
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Schaller D 1985. Wing Evolution. In: Hecht, M., Ostrom, J.H., Viohl, G. and Wellnhofer, P., eds, The Beginning of Birds. Proceedings of the International Archaeopteryx Conference, Eichstätt 1984, (Freundes Jura Museum, Eichstätt), 333–348.
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

Flightless pterosaur – svp abstracts 2013

Now it’s in the published literature… the first known flightless pterosaur

Figure 2. Sos 2428. The flightless pterosaur. Click for more information and in situ photos.

Peters (2013) wrote: “Jura Museum Solnhofen Sammlung (SoS) 2428 is a largely complete, crushed, Solnhofen pterosaur. It was previously considered another specimen of Ardeadactylus (formerly Pterodactylus) longicollum, neotype: Staatliches Museum für Naturkunde, Stuttgart (SMNS) 56603. However, a closer look reveals important differences. The skull is longer than the cervical series in SoS 2428, but not in Ardeadactylus. The slender cervical ribs are each a centrum length in SoS 2428, but they are much shorter in Ardeadactylus. The parasagittally compressed dorsal vertebrae comprise only 40% of the torso length in SoS 2428, but 66% in the more typical pterosaur, Ardeadactylus. Conversely, in SoS 2428 the robust sacral series extends for 60% of the torso, 34% in Ardeadactylus. In SoS 2428 the dorsal ribs, sternal ribs and gastralia are relatively twice the lengths of those found in Ardeadactylus. The pectoral girdle is gracile in SoS 2428, with a scapula and a coracoid half the width of those same elements in Ardeadactylus. The forelimb (wing) elements are likewise less than half the length and width of those in Ardeadactylus. The wing finger (manual digit 4) is further reduced relative to the rest of the wing. When folded, the unreduced first wing phalanx extends back to the carpus. However, the second wing phalanx is half that length. The third phalanx is half the second and the fourth is less than half the third. Thus, when folded, the distal tip of the reduced wing finger extends just to the elbow. By comparison, in Ardeadactylus the elbow meets the middle of the second wing phalanx and the two distal phalanges nearly double that length. In SoS 2428, the free fingers, digits 1-3, are not reduced. Matching the elongated sacrum in SoS 2428, the hyperelongated ilium extends for 60% of the torso length. However, the much smaller pubis, prepubis, ischium and femur are similar in size to those same elements in Ardeadactylus. In SoS 2428 the distal tibia and pes are not preserved. When reconstructed, SoS 2428 has a relatively longer and wider torso than any other known pterosaur. It also has a reduced wing, half the length and half the chord
of the wing of Ardeadactylus when scaled to the same torso length. Such a reduced wing and enlarged torso make the prospect of flight rather doubtful by comparison. Moreover, with such morphological differences, SoS 2428 is clearly a distinct genus.”

Earlier we discussed this specimen. The poster for the flightless pterosaur included all the detail possible including color photos in high resolution. Tracy Ford was kind enough to put up this poster because I could not attend the SVP symposium. He said a few people walked by saying they did not believe it.

Doubt? Not convinced?
Belief, remember, is in the realm of religion. In Science you can confirm or refute a claim by repeating the experiment or observation. In this case, if you “don’t believe” the traits presented in this abstract, I encourage you to go visit the specimen and apply whatever technique works best at pulling data out. Whatever you get, send it to me. Then we can discuss this together, whether refuting, modifying or confirming the claim here.

Belief, in science, should never part of the equation. If you have evidence refuting this claim, please bring it to my attention. Changes will be made. Otherwise, join the celebration. Finally, we have a flightless pterosaur!

References
Peters, D 2013. A flightless pterosaur. Journal of Vertebrae Paleontology abstracts 2013.

Flipped wingtips – Rio Ptero Symposium

Continuing our look at the Rio Ptero Symposium abstracts…

Hone et al. (2013) proposed a reconstruction of the tiny Rhamphorhynchus specimen, Bellubrunnus with wing phalanx four (m4.4) concave anteriorly — in other words, different from all other pterosaurs (in which m4.4 is either straight or convex anteriorly). Hone et al. proposed that odd reconstruction because that is exactly how the wingtip appears in the fossil (Fig. 1).

In an attempt at explaining away the autapomorphic concave anteriorly curvature, which would have played havoc with the wing membrane, Hone et al. (2013) promoted the idea that the wingtip might straighten out under load, pulled and straightened posteriorly by a stretching wing membrane under tension, the way an archer’s bow bends when the archer pulls back the bow string.

There’s some confusion here,
so let’s take the problem apart with DGS.

Figure 1. Click to enlarge. Bellubrunnus (center) in situ. The Zittel wing (left) and the WDC specimen (right) showing how the interphalangeal joints are typically pointed posteriorly, toward the membrane. The Bellubrunnus specimen appears to break that model (see insets at bottom), but note the right wing has been flipped (ventral surface in red) and the distal half of the left wing has been flipped (ventral surface in red) based on the shape of the wing joints. This makes the wing tips typically convex anteriorly when flipped back to their in vivo orientation. 

Clue #1. The wing tips are not exposed in dorsal view
While the fossil is largely preserved in dorsal view, the left distal elements, m4.3 and m4.4 (in red) have been twisted axially 180 degrees, exposing their ventral surfaces. The right wing is exposed ventrally (in red) in its entirety. We know this because of the shapes of the joints. Examples (Fig. 1) from the Zittel wing and the WDC specimen illustrate what the unrotated wing joints look like. The largest, most pointed parts of the wing joints generally point toward the wing membrane. That’s basic pterosaur morphology. That’s how you can tell dorsal from ventral… most of the time.

The confusion arises
from the proximal process of the left m4.4 which is larger and more pointed — the opposite of most pterosaur wing joints. This is what Hone et al. keyed on. The right wing doesn’t show any expansion of the joint in either direction. So it is oddly uninformative. Basically Hone et al. chose that joint expansion clue on the left m4.4 to decide that joint was on the wing phalanx posterior rim, giving it a concave anterior bow. There’s a certain logic in that that I can appreciate. But then, we have to deal with the extreme oddity of concave wing tips!

Let’s look at some other related wing tips.

Figure 2. M4.4 from another Rhamphorhynchus, showing the joint can expand both anteriorly and posteriorly.

Other Rhamphorhynchus specimens (Fig. 2) demonstrate that the proximal joint of m4.4 can expand in both directions. This may solve the problem. A reconstruction (Fig. 3) also helps.

Figure 3. A reconstruction of the new pterosaur, Bellubrunnus with wingtips (m4.4) convex anteriorly as in most other pterosaurs. Otherwise we’ll have problems with the trailing wing membrane.

A sister taxon – Qinglongopterus
The large pterosaur tree nests the small Qinglongopterus as a sister to Bellubrunnus and it also has a double-expanded proximal joint on m4.4 (Fig. 4). So, now, if you’re a paleontologist, you have to decide:

1. did the preparator knock off the joint expansion on the concave side of the Bellubrunnus left wing during prep? … and also both joint expansions on the right wing?
2. are the wing tips flipped ventral side up? (See Fig. 1).
3. did Bellubrunnus have an odd sort of convex anterior wing with the joint expansion anteriorly and only on one wing?
4. or did Bellubrunnus have a concave anteriorly phalanx, different than all other pterosaurs?

Hone et al. chose #4. Then they had to explain it away but employing the “under tension” hypothesis. Occam’s razor might have helped here. It’s like trying to explain away a folded wing membrane as “membrane shrinkage” during fossilization, which  Elgin, Hone and Frey (2011) did earlier.

Autapomorphies
As I learned with regard to that funny little “anterior process” on the ilium of Cosesaurus that turned out to be the stem of the prepubis, autapomorphies can turn out to be mistaken interpretations. If you find an autapomorphy, a trait that no other sisters have, like a concave wingtip, it’s best to think through the possibility that you may have made a mistake. Unfortunately, Hone et al. did not explore all the possibilities, nor did they find the same trait on the other wing or other sister taxa. There is something odd about that one joint, but nothing odd about the convex anterior phalanx.

It’s always good to discover things, but potentially embarrassing when someone points out “kind sir, you have it upside down.”

Once pterosaur wings evolved, very little changed about them other than the relative sizes of wing bone elements. An anteriorly concave wing would have been quite a difference — and one that was reversed back again in descendant taxa, as no later Rhamphorhynchus specimens share this trait.

This also hearkens back to Bennett 2008
who claimed the pterosaur wing finger and membrane began as part of a supinated limb (in other words, not facing the substrate) — but lost the forward-pointing claw from the wing finger because it would have pointed forward hooking on nearby tree trunks — and the naturally concave palmar bow of the the terminal phalanx would have had to reverse to convex forward — along with turning the natural flexion of the metacarpophalangeal wing joint to hyper-hyper extension. All this completely imaginary hoo-hah is detailed here.

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
Hone DWE, Habib MB and Van Rooijen M 2013. Wingtips in Pterosaurs: functional and ecological implications. Rio Ptero Symposium 77-78.

.

 

Zittel Wing – Rio Ptero Symposium

Earlier we looked at another Rio Ptero Symposium abstract. There are several more to come.

Chris Bennett (2013) took a fresh look at the century-old Zittel wing of Rhamphorhynchus (Fig. 1). He determined that we need to flip our view of it. According to Bennett, those aren’t straw-like actinofibrils ribbing the wing that contract to make the wing extensible. Rather those are narrow spaces between popsicle-stick like actinofbrils that make the wing “inextensible.”

Figure 1. The Zittel wing simply flipped to give the false image of dips (upper image) or true image of ridges (lower image) in the wing membrane due to light direction that the eye assumes to come from above the image. Note the round bones give away the true light direction. Inserts show Bennett’s new view (upper image) of wide aktinofibrils. Lower image shows traditional view of straw-like aktinofibrils that enable wing reduction.

Bennett notes, “actinofibrils were long flattened bands of keratin” and “The raised longitudinal strips are not the actinofibrils, but rather the grooves between the ridges are impressions of the actual actinofibrils and thus for 120 years we have had it upside down and backwards” and  “Thus its size and shape of the Zittel wing is essentially as in life.” Of course that flies against all the other examples of pterosaurs in which the wing folds to near invisibility.

This is not Bennett’s first foray into radical and irrational hypotheses. His autapomorphic interpretation of the flathead anurognathid skull and his completely imaginary hypothesis on pterosaur wing origins are among his earlier ventures. It’s hard to reconcile Bennett’s inextensible wing with the several other examples in the fossil record of extensible wings that collapse into almost nothingness.

On the other hand
in the same Rio Ptero volume Bennett successfully argued against the presence of an antorbital fossa and mandibular fenestra in basal pteros, as discussed earlier here.

References
Bennett SC 2013. If 6 was 9: Turning our interpretation of the Zittel wing upside down. Rio Ptero 2013 Short Communications. 22-25.

Alpine Swifts and Pterosaurs

Alpine Swift (Tachymarptis melba) on the wing for 7 months at a time! Check out that wing shape. Remind you of anything prehistoric?

An interesting NatGeo post on the Alpine Swift (Tachymarptis melba) and its incredible but true 7 months (200 days) on the wing (Liechti et al. 2013) raised my curiosity about what sort of wing must such a bird have?

Turns out to have a very pterosaurian wing (short chord version) in ventral view. Nat Geo reports, “Their long wings make them fast and manoeuvrable, allowing them to scythe through the air in search of small insects and other “aerial plankton”.

And why do they fly continuously? Again, Liechti has speculations rather than answers. They may exploit food sources that other birds can’t touch, avoid predators by flying through the night, or stay beyond the reach of parasites like malarial mosquitoes. “These aren’t very convincing,” he admits, “but for sure, there’s a cost to staying in the air, so there must be a benefit.”

Swifts are apodids, famous for their tiny feet (they don’t perch that often). That takes us to the pterosaurs with tiny feet and spindly legs, the ornithocheirids (Fig. 2, 3).

Worth comparing for wing shape and foot size.
Evidently these large pterosaurs were likewise rarely grounded, based on their tiny feet and giant wings, especially compared to other pterosaurs.

Figure 2. The ornithocheirid pterosaur, Arthurdactylus. Note the tiny size of its feet and the huge wings. Like a swift, this pterosaur could have slept while on the wing. The spindly fingers were no good for grappling tree trunks.

Awkward on the ground.
Graceful in the air. This is the reason why the ornithocheirid humerus is so much larger than the femur – not the forelimb launch hypothesis! They put everything into their wings, which transport them to food. Their legs simply enable them to walk out of their eggs.

Figure 2. Arthurdactylus in dorsal view while flying. Note the knife-like wing shape, that could be maneuvered, like that of a sail plane or swift. Wings back = less drag, greater speed.

Basically the pterosaur wing in ornithocheirds is a tapering cone, with a large diameter proximally and a tiny diameter distally. This has proved to be a very strong structure from outstretched traffic lights to fishing rods.

Outstretched to swept back
As in swifts, the wings of pterosaurs could have maneuvered in flight from strictly lateral to backswept. Each configuration has their own use, advantage and disadvantage.

References
Liechti, Witvliet, Weber & Bachler 2013. First evidence of a 200-day non-stop flight in a bird. Nature Communications.http://dx.doi.org/10.1038/ncomms3554

Pterosaur dipping and skimming – first for drinks, then for floating insects

Last week’s (Sept 18) Nova program on PBS entitled, “Earthflight” showed swallows, with their tiny little beaks, dipping for water while on the wing (see video here). Later the swallows dipped for floating mayflies. Others took quick baths by diving an inch below the water then reemerging without losing too much momentum.

Click to view. From the BBC special on birds entitled, “Earthflight.” Swallows drinking while on the wing. Note the teeny tiny beaks.

So why can’t certain pterosaurs, like Rhamphorhynchus and others, skim and dip (there is a spectrum between the two based on speed of attack) for surface-dwelling fish? Especially when a fish is found in the throat and belly? We looked at this earlier. The swallows, with their tiny wide, unspecialized for dipping beaks, demonstrate that a flying animal does not need a special beak shape.

Figure 2. Manipulating the bones of the fish-eating Rhamphorhynchus into a skimming configuration while staying airborne.

Humphries et al. (2007) tried to show that skimming would not be likely for pterosaurs. They used math. Sometimes math isn’t the key. They used morphological comparisons to the modern skimmer, Rynchops, which is ideally suited to high-speed skimming on windless ponds. Swallows demonstrate that’s THAT important. We considered pterosaur skimming earlier here.

Earlier we talked about the key: windspeed. It doesn’t equal groundspeed (or waterspeed) when flying into a breeze or steady wind. A steady breeze at the best glide speed can equal a hover over a particular spot. A little speed isn’t a bad thing either. I’m sure pterosaurs found the ideal circumstances and took advantage of them.

So, like birds, pterosaurs graduated from taking drinks on the wing, to taking floating insects on the wing, to taking surface-dwelling fish while on the wing and some even dived like gannets deep beneath the surface (gannets can descend 70 feet btw). That’s a nice variety of niches.

Nyctosaurus and Pteranodon
On this subject, it’s interesting to note, once again, that Nyctosaurus had a longer mandible and Pteranodon had a longer rostrum, both sharp like a sword and sharpened with a single sharp tooth in the tips of both jaws. Rhamphorhynchus (Fig. 2) does not have these anterior teeth, but has a rostrum and dentary tipped with keratin extensions.

References
Humphries S, Bonser RHC, Witton MP and Martill DM 2007. Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biol 5(8): e204. doi:10.1371/journal.pbio.0050204 online

Pterosaur ornithopters: lessons learned

Following in the success of the Dr. Paul B. MacCready‘s 1985 flying Quetzalcoatlus ornithopter (Fig. 4), a few years ago there was an attempt at getting another very complex pterosaur ornithopter to fly.

Margot Garritsen is a Dutch engineer and Stanford professor who led a team intent on building a flying pterosaur based on Paul Sereno’s ornithocheirid from the Sahara. They were counting on greater success with lighter materials and a more accurate wing movement with not one, but five wing joints for flight control. Several paleontologists were team members and Hall Train provided some of the mechanics. So it had everything going for it. The project was featured in the IMAX film “Sky Monsters.”

Figure 1. The Stanford pterosaur ornithopter moments after dropping from its mothership. On this second attempt all the fur and non-essential material had been removed. A removable horizontal stabilizer with twin rudders is added as a sort of stabilizing tail. Note, this is a deep chord wing membrane configuration, which pterosaurs did not have.

Unfortunately
the new and improved ornithopter failed to flap and failed to fly.

Another inventor, Kazuhiko Kakuta
using a much simpler design (Figs. 2, 3), created a successfully working ptero-ornithopter.

Cheaper. Simpler. Less accurate.
Actually, almost nothing is more pterosaur-like than bird-like here other than the fashioned crest. The key here appears to be the successful creation of sufficient thrust and lift without a cambered airfoil — as in any toy bird-like ornithopter.

For those interested ornithopters are explained here.

Figure 2. Pterosaur ornithopter. This model flies well and for good reason.

An efficient flapping wing must be able to flex and/or rotate: if a static wing is kept at the same angle while moving up and down, it will produce no net lift or thrust. Flexible wings can attain efficiency while keeping the driving mechanism simple. In Ornithopters its the ventral and dorsal curling of the wing during flapping that changes the wing shape and creates lift and thrust.

Read about the model maker here with his other pterosaur YouTube videos listed.

Figure 3. Click to see video. This pterosaur ornithopter folllows the basic plan of bird ornithopters in having a stiff leading edge and a flexible trailing edge. There’s no need for complex flapping cycle. Up and down works pretty well.

Most ornithopters have extremely simple motions and deep chord wing shapes.

What would happen if the wing had a camber, a narrow chord and a spoon-shaped wing tips, as in pterosaurs? So far, except for the MacCready invention (Fig. 4), no one has built a short chord. long wing ornithopter and even the MacCready invention did not have the proper pterosaur wing shape and leg configuration.

So there’s an opportunity here to do something great for an engineering student: replicate a real pterosaur and make it flap using simple ornithopter techniques.

Figure 4. Quetzalcoatlus model ornithopter by Paul Macready getting walked to its take-off point. The tucked in legs are based on the bird-like hypotheses of Dr. Kevin Padian, now widely regarded as wrong. No fossils preserve this configuration. Rather the legs would have been more or less splayed in flight.

Dr. Paul B. MacCready is famous for creating a dang big ornithopter the size and shape of a Quetzalcoatlus back in 1985. Here it is on YouTube. Here is a pdf of the project. It flew very successfully. There’s a Popular Science article here about MacCready’s work.

Still…
It would have been better to extend those hind limbs like horizontal stabilizers on airplanes (Fig. 5), but they were listening to Kevin Padian back then and he saw pterosaurs as very bird-like. Now that we know they were more lizard-like, pterosaur configurations have changed. 

Figure 5. Rhamphorhynchus model by yours truly. Note the narrow chord long wings and feet splayed like a horizontal stabilizer. The raised elbows produce more camber proximally. The tail is an unnecessary secondary sexual characteristic.

For a change of pace, here’s a video that shows a small simple pterosaur-shaped airplane powered by propellers. So basically, it’s an airplane.