Flugsaurier 2018: Los Angeles County Museum

Flugsaurier
is a meeting of those interested in pterosaurs that happens in another part of the world every few years. I went to the first few. Saw a lot of specimens. Met a lot of colleagues. Produced a few abstracts and gave some presentations.

Over the next few days
there’s a Flugsaurier meeting taking place in Los Angeles. Many well-known and not-so-well known speakers are giving presentations this year. I will not be among them. Why?

So far as I know,
all of the conveners and many of the presenters continue to ignore a paper I wrote 18 years ago on the origin of pterosaurs from fenestrasaurs, not archosaurs. Other papers followed on wing shape, trackmaker identification and other topics, all supporting that phylogenetic hypothesis of relationships. Evidently workers would prefer to hope that pterosaurs arose from archosaurs close to dinosaurs. This is not where the data takes anyone interested in the topic who is not a party to taxon exclusion.

In addition, several of the conveners

1. subscribe to the invalid quad-launch hypothesis
2. the bat-wing reconstruction of the brachiopatagium.
3. they believe that pedal digit 5 framed a uropatagium.
4. They refuse to add tiny Solnhofen pterosaurs to their cladograms.
5. They refuse to add several specimens of each purported genus to cladograms—and because of this they don’t recognize the four origins of the pterodactyloid-grade (not clade).
6. They still don’t recognize that pterosaurs grew isometrically.
7. They still don’t accept that pterosaur mothers retained their egg/embryo within the body until just before hatching (a lepidosaur trait).
8. They still don’t accept that pterosaur bone fusion patterns follow lepidosaur, rather than archosaur patterns.
9. They accept the idea that giant eyeballs filled the anterior skulls of anurognathids, not realizing that the supposed ‘scleral ring’ on edge of the flathead anurognathid is actually the mandible and tiny teeth.
10. They reject any notion that all basal and some derived pterosaurs were bipedal, despite the footprint and morphological evidence proving bipedal locomotion.
11. They all hold out hope that the largest azhdarchids could fly.
12. I was going to say that all workers believe that crest size and hip shape identify gender, when the evidence indicates these are both phylogenetic markers, but then I found an abstract in 2018 that casts doubt on the gender/crest/pelvis hypothesis. So there’s hope.

That’s a fairly long list of ‘basics’
that most pterosaur workers ‘believe in’ despite the fact that there is no evidence for these false paradigms — but plenty of evidence for the lepidosaur origin of pterosaurs, from which most of the above hypotheses follow.

I am not attending Flugsaurier 2018
because the convening pterosaur workers deny and suppress the data listed above. Plus, I can more actively and thoroughly test assertions made during the conference from ‘my perch’ here in mid-America.

Good luck to those attending. 
Test all assertions and hypotheses, no matter their source.

A new Rhamphorhynchus with soft tissue: TMP 2008.41.001

A new PeerJ paper by Hone, Henderson, Therrien and Habib (2015) reports on a new complete, articulated (with a crushed and scattered torso) Rhamphorhynchus specimen, TMP 2008.41.001, the Tyrrell specimen (Fig. 1).

Figure 1. The new Tyrrell specimen of Rhamphorhynchus.

One species
Hone et al report, “Here we follow Bennett (1995) in considering all Solnhofen specimens of Rhamphorhynchus to belong to a single species, R. muensteri.” This is wrong and lazy. Phylogenetic analysis (Fig. 2), which Hone et al do not attempt, divides this genus into several clades. Even the feet have distinct pedal proportions. The Tyrrell specimen nests at the base of the JME SOS 4785 (Darkwing specimen) clade and is similar in size to other clade members.

Figure 2. Cladogram of Rhamphorhynchus. See, they’re not all one species. And phylogenetic miniaturization occurred at the genesis of this genus.

Juveniles and subadults?
Hone et al. report, “The genus has previously been split into a dozen or more species but these have convincingly been shown to consist of juveniles and subadults of a single species (see Bennett, 1995 for a review).” This is also wrong. We know from several single genus bone beds that hatchlings and juveniles of all tested pterosaurs had adult proportions. We know from phylogenetic analysis that a juvenile Rhamphorhynchus was recovered in phylogenetic analysis because it scored identical to an adult but was less than half as tall.

The specimen used to be in a private collection
of the quarry owners. It was discovered in 1965 and recently sold to the Tyrrell. It is preserved in ventral view with light impressions of wing membranes and a trapezoidal tail vane.

The skull
Hone et al. report, “Some sutures in the skull can be tentatively identified but these are mostly not clear, either because they are being obliterated as a result of cranial fusion during ontogeny, or owing to crushing of elements.” Here (Fig. 3). DGS colorizes the skull bones. I did not notice any obliteration in the sutures.

Figure 3. Rhamphorhynchus Tyrrell specimen after DGS colorizing of the bones.

The teeth
Hone et al. considered the tooth count (twelve uppers, ten lowers) “higher than normal” for Rhamphorhynchus (ten uppers, seven lowers), but the extras appear to be incipient teeth or tooth tips from the right side of the skull.

Sacrum
Hone et al. identify four sacrals (Fig. 5), not counting the anterior vertebrae that lie between the ilia and sends out processes to the anterior ilia.

Caudals
Hone et al. report, “The divisions between the vertebrae are difficult to distinguish along the majority of the length of the tail and parts are covered by the left pes, so a vertebral count is not possible.” I had less of an issue while applying DGS (Fig. 4). But then I had only a jpeg, not the real thing. The photo looks good. Is this a case where DGS trumps first hand observation? See figure 6 for comparison.

Figure 4. Rhamphorhynchus, Tyrrell specimen, caudals. They are distinct from one another contra Hone et al. 2015. Click to enlarge.

Dorsal ribs
Hone et al. report, “Numerous dorsal ribs and gastralia are preserved on the specimen but a count is not possible given that many elements overlap one another.” This is exactly what DGS does best (Fig. 5) because the eye get overwhelmed by the chaos and colors segregate and ultimately simplify the issue.

Figure 5. Torso of Rhamphorhynchus from Hone et al. 2015. Above as originally interpreted. Below using DGS. What Hone et al. identify as a mc (metacarpal) is the radius + ulna. Scale bar = 2 cm. One rib is actually a prepubis. It is much more robust then even the anterior ribs. A fifth acral rib is identified here. The coracoids are in light blue. The light gray areas maybe an egg. A smaller second possible egg is also in gray. The sternal complex (not just the sternum) appears to be broken into several parts. Fibula parts are identified along with a second ischium.

Sternal complex
Hone et al. refer to the sternal complex as the sternum. That’s inexact. They know it’s not just a sternum, but also includes the clavicles and interclavicle. Nesbitt (2011) assumed these latter elements were missing from pterosaurs in his analysis, so such deletions have real world consequences in cladograms.

Figure 6. Rhamphorhynchus Tyrrell specimen right wing GIF movie showing vane and wing tip ungual visible in high contrast. Note the lack of differentiated caudal vertebrae. Click to enlarge.

Wings and their membranes
Hone et al. identify an ulna where an ulna + radius is present, as described in their text. In prior works these authors have supported the deep chord wing membrane false hypothesis, despite all evidence demonstrating otherwise. Here again is another narrow chord wing membrane with a direct connection to the elbow. That the knees are drawn up does not negate this observation, which is universal in pterosaurs.

FIgure 9. Rhamphorhynchus left wing GIF movie (click to enlarge) showing radius + ulna, pteroid and standard narrow chord wing membrane.

Wing tip
Hone et al. note that both wings terminate in a squared off tip. They were not present when this specimen was prepared 50 years ago. I agree that no wing tip ungual is readily apparent here, as opposed to the many seen on several specimens previously. If you bump up the contrast on the matrix, several ungual candidates appear (Fig. 10). The “squared-off tip” described by Hone et al. looks like any other articular surface, as in the other interphalangeal joints on the wing. This should have been noted.

Figure 10. Right wing tip of Tyrrell specimen of Rhamphorhynchus showing blunt tip and, with higher contrast, several ungual candidate impressions.

 

Figure 11. Pelvic elements of Rhamphorhynchus, Tyrrell specimen, replaced to their in vivo positions in lateral view along with the two possible egg candidates for comparison to the pelvic opening. Seems like a good fit. The prepubis, originally identified as a rib, has no counterparts among the ribs. It is more robust and straighter.

Pelvis
Hone et al. report, “The pelvis is partially disarticulated and some elements appear to have been lost.” The ilia are both easy to see. Hone et al. report, “The proximal part of the right pubis is articulated with the right ilium, but only the articular end is visible and the rest appears to be hidden below other elements.” I did not see that. I did see both pubes scattered in the mix (Fig. 5). They are not readily apparent. Hone et al. report, “Only one ischium (?right) can be identified.” I found both (Fig. 5) parallel to each other. Hone et al. report, “Both prepubes are preserved but are in poor condition and covered by other elements. They are in close association but are not articulated with one another and lie posterior and ventral to the sacrum.” The authors did not identify the prepubes in their tracings. In ventral view the prepubes should not be covered by other elements (which elements?). I found one prepubis, misidentified as a rib by Hone et al. and the other one where they said it was. I don’t think they realize how large the prepubes are in this species of Rhamphorhynchus, which is a ‘chubbier’ pterosaur than most others owing to its long ribs, gastralia and deep prepubes. No other ribs are robust like the prepubis. And all of the anterior ribs, those likely to be more robust, but are not in this species, are accounted for. Plus it matches the darkling prepubis (Fig. 12).

Figure 12. The darkling specimen of Rhamphorhynchus, very similar to the Tyrrell specimen, showing the depth of the gastralia and prepubis.

The foot
traits alone nested the Tyrrell specimen within its clade as this is the only clade with penultimate pedal phalanges longer than the others (Fig. 13). Click here to see others.

Figure 13. Pes of the Tyrrell specimen of Rhamphorhynchus.

The wing membrane
Hone et al. report, “Each wing has a more narrow chord along most of its length than seen in some specimens of Rhamphorhynchus (e.g., BSPG 1938 I 503a, the ‘DarkWing’ specimen—Frey et al., 2003) suggesting some postmortem shrinkage of the membranes (Elgin, Hone & Frey, 2011).”

There is no shrinkage!
Hone et all are refusing to face the facts. They are making up scenarios to avoid the narrow-wing morphology (Peters 2002). This pterosaur, like all others, has a narrow chord wing membrane. Hone et al acknowledge that. And so does the dark-wing specimen, as documented earlier and shown below (Fig. 14). When the wing is outstretched, as if in flight, the membrane goes with the wing finger and it is stretched between the elbow and wing tip. Any other attachment points needlessly complicate matters. Any other scenarios are excuses and just-so stories.

Figure 15. The darkwing specimen of Rhamphorhynchus. Top: in situ. Middle: Soft tissues highlighted. Bottom: Neck and forelimb restored with wings outstretched. This is another narrow chord wing membrane when the parts are restored to their in flight position. The arrows show how much the wing would have to stretch to attach to the ankle. But there’s no muscle and bone to stretch it. Remember, in flight the tibia stick almost straight out laterally,

Biut wait… there’s more!
Hone et al. report, “Proximal to the elbow, the right tenopatagium (Fig. 6) is rather less clearly preserved than the left actinopatagium (Fig. 5), but does appear to meet the left ankle as is considered common, or even ubiquitous, for pterosaur wing membranes (Elgin,Hone & Frey, 2011).” Yeah, right… This is really reaching. This is why these guys keep rejecting my papers and why I don’t attend pterosaur symposia. They are adamant about rejecting anything I have published on. Evidently, I have (figuratively) poisoned the well. And that’s a sorry state of affairs. They will never say, “well, I guess Peters 2002 was right about the narrow chord wing membrane. It’s right here in front of us.”

You should know
Hone et al. report, “Furthermore, at least some parts of the wings have been covered with some form of transparent preservative and brush marks (e.g., swirls) are clearly visible in places on the matrix.”

Uropatagia are preserved
But due to the extreme bending of the knees, their shape cannot be determined. Hone et al. provided an extreme closeup of fibrils in a uropatagium (their figure 7, but note the singular state here as they falsely believe, based on the Sordes error, that one membrane extended from leg to leg). They reported the element on the right is the right tibia, but the right tibia is devoid of tissue, as far as I can tell. I was unable to match the extreme closeup to any other wider view shots. There does appear to be soft tissue between the left femur and tibia (remember the specimen is on its back so left is right and right is left). Their figure 8 has a wider view and represents the left tibia. Still the fibrils are close to the tibia and they provide no evidence that these are not separate uropatagia, as in all other pterosaurs.

Gut contents
Hone et al report gut contents of an indeterminate vertebrate. “most of these are distorted and difficult to identify though their overall shape appears to be that of squat cylinders. Their exact identity cannot be determined as they are incomplete and partially covered by other elements, and much of the chest cavity has calcite crystal buildup. –– These bones may represent fish or tetrapod elements, but are not part of the pterosaur as they match none of the dissociated or missing material (ribs, gastralia, sternal ribs, pteroids, pelvic elements) but instead are a sub rectangular series and associated subcircular elements that collectively may be vertebrae (Fig. 3).” Rhamphorhynchus is typically considered a fish eater as fish have been found within certain specimens. ‘Hooklets’ [= simple spikes and hook-like shapes] are found by the thousands in the coprolites. Hone et al. report, “If the diagnosis is correct, this is the first recorded coprolite for any pterosaur.”

Odd that the torso should be so upset, but the soft coprolites untouched.

Hone et al. did not consider the possibility
of an internal immature egg. The item has an oval outline (Fig. 11). And there may be a second smaller, even more immature egg in the mix (Fig. 11). Hard to tell in all that chaos.

Ontogeny
Hone et al. are correct in stating the Tyrrell specimen is adult or nearly so. But sutures are not a reliable indicator of ontogeny. Several clades fuse early and others never fuse, patterns common to lepidosaurs, not archosaurs.

Found typos
Perhaps these can be corrected since they are online:

1. “several specimens seen to have consumed fish”
2. The uropatagium has become displaced relative to the bones even in some exceptionally preserved specimens (e.g., Sordes PIN 2585-33). The holotype is PIN 2585-3). I find no record for #33 on the Internet.

References
Hone D, Henderson DM, Therrien F and Habib MB 2015. A specimen of Rhamphorhynchus with soft tissue preservation, stomach contents and a putative coprolite. PeerJ 3:e1191; DOI 10.7717/peerj.1191

Mark Witton’s “Pterosaurs” – a book review part 1

Dr. Mark Witton is fantastic artist and devotee of pterosaurs. He has a new book called Pterosaurs (with an Amazon.com preview). I’ve ordered the book and will make an in depth report after it arrives. The following is based on the online preview of chapter 1. Witton’s writing style is entertaining and engaging. The book should have popular appeal on that level.

The cover portrays a magnificent crested Nyctosaurus at sunrise or sunset. Gorgeous!

Then things tumble.

Witton’s Table of Contents shows an embryo Pterodaustro with a very short rostrum, unlike any Pterodaustro I’ve ever seen. And I’ve seen the embryo. The rostrum extends nearly the entire length of the egg. An agreement with Laura Codorniú prohibits me from publishing the image until she does, but the reconstruction of the long-beaked embryo Pterodaustro is based on that tracing. As we learned earlier, pterosaurs grew isometrically, resembling their parents on hatching.

Witton’s Rhamphorhynchus image on page 2 portrays the infamous cruro/uropatagium, a membrane spanning the hind limbs and not including the tail. The image also includes the infamous deep chord wing membrane, for which there is no evidence whatsoever as the Sordes situation was falsified. Witton’s two Rhamphs also have much shorter wings than any Rhamphorhynchus I’ve ever seen. One of Witton’s wonders has brought its wrists (carpals) in close to the base of the neck, which is novel, at least, but kills the tension on the extensor tendon that keeps the wing membrane aerodynamic. As in birds, when the elbow flexes, the wing folds. Having the wings fold in flight isn’t bad. Birds do it all the time for a brief low drag rest. At least the feet are properly positioned in Wittons’ illustration.

Page 3 portrays several dozen pterosaurs doing the forelimb leap that is such a travesty and fantasy that I slap my head every time I see it again and again. It has become firmly entrenched. Gadzooks@!# what is the ptero-world coming to?

Page 4 has a fine picture of Pterodactylus antiquus, the first pterosaur known to science, with a big round head crest. Not quite ready to buy into that one quite yet. Some Pterodactylus did have a crest, but not that one.

Page 12 portrays a hypothetic pterosaur ancestor. It looks like Peteinosaurus with a short digit 4 leaping from a branch (using muscular hind limbs). The caption reads, “The fossil record has yet to reveal an “intermediate” between fully formed pterosaurs and possible ancestors, meaning we can only speculate on their anatomy and appearance.” And once again, pterosaur professors are casting a blind eye toward the hard evidence presented in the large reptile tree where dozens of ancestors are lined up. As you’ll recall, ludicrous as it sounds, we can even put turtles up as the closest known sisters to pterosaurs if we delete all the other sisters and candidates from the new Lepidosauromorpha, as demonstrated here. This just proves that pterosaur workers are actively avoiding the issue and the answer. But, I have to say, it’s a beautiful and evocative image that Witton has created, wrong though it may be.

Page 16 portrays three purported pterosaur ancestor/sisters, Sharovipteryx, Euparkeria and Scleromochlus. Witton calls Sharovipteryx an archosauromorph protorosaur, when it is neither. It is a fenestrasaur tritosaur lepidosaur, as we learned earlier. Euparkeria is closest to erythrosuchids, about as far from pterosaurs as one could imagine. Scleromochlus, shown hopping in Witton’s illustration with a dino quadrate leaning the wrong way, is a basal crocodylomorph. Witton strongly leans toward the “pterosaurs are ornithodires” direction despite the tiny hands and lack of pedal digit 5 in Scleromochlus.

Witton takes aim at my placing pterosaurs within the Squamata as the most unlikely hypothesis currently under consideration. See a recent post on this here. Witton writes, “There seems little similarity between the skulls of pterosaurs and the highly modified, mobile skulls of squamates or any similarity between the trunk and limb skeletons of each group.” Well, frequent readers will know that pterosaurs are tritosaur lepidosaurs, an outgroup clade to the two that make up the Squamata, the Iguania and the Scleroglossa. Pterosaurs are neither of these. Tritosaurs do not have the mobile skulls found in some squamates. They also don’t have the fused tarsals of squamates. They are distinct. Witton has whitewashed the tritosaur fenestrasaur hypothesis with this “red herring,” while virtually ignoring the fenestrasaurs, following in the less than noble footsteps of our colleague Dr. David Hone, whose exploits you can read about here. In chapter one, at least, Witton avoids any discussion of the pteroid and prepubis in Cosesaurus and other fenestrasaurs. Why should he ignore these key and readily observable traits? Dr. Pierre Ellenberger saw them first without recognizing their significance.

Page 17 Witton then discusses the possible protorosaur origins of pterosaurs, pointing to the shared trait of an elongated neck and forgetting the not-so-elongated neck of the basalmost  pterosaur, MPUM6009.  Witton points up the “fact” that protorosaurs lack an antorbital fenestra, but recent finds show that two protorosaurs had such a fenestra by virtue of convergence (really a side issue of little consequence). Witton finishes with protorosaurs by noting the body shapes are not at all pterosaurian, which is true.

Witton invites a closer look at Sharovipteryx and notices similarities to pterosaurs in the hind limbs and their membranes, but notes, “It’s hard to find other features that reliably link this animals with pterosaurs.” He may not have looked at the actual specimen as I have. Evidently he did not notice the ilium was anteriorly elongated, prepubes were present, more than five sacrals were present, the tail was attenuated with parallel chevrons, the bones were hollow, the feet have the same morphology as pterosaurs with a short metatarsal 5 and an elongated and robust p5.1 as obvious and compelling similarities. Once again, the blind eye rules. Witton reports that the Sharovipteryx skull lacks an antorbital fenestra and the foot is unlike that of any pterosaur. Where does he get his information? Certainly not from any sort of direct observation or adherence to the literature. Of course he doesn’t back up any of this with evidence. Witton concludes by noting that gliding with hind limbs is unique, failing to find parallels in Microraptor and the uropatagia of fenestrasaurs including pterosaurs. Sharovipteryx had fore limbs. Witton just doesn’t know or doesn’t show what they look like. But you can see them here.

Page 18 Witton prefers the archosauriform ancestry hypothesis due to the shared features of an antorbital fenestra and reduced bone counts in the fifth pedal digit, perforated lower jaws, and “many other anatomical similarities.” Really? Witton equates an evaporating pedal digit 5 in archosauriforms with the robust element in pterosaurs (and, of course he doesn’t count the ungual on the pterosaur digit). A robust pedal digit 5 is also found in Huehuecuetzpalli and all the tritosaur lepidosaurs that followed (except Macrocnemus and the drepanosaurs). Why doesn’t Witton consider these and put some study into them? The antorbital fenstra of archosauriforms is always (except for proterosuchians) surrounded by a fossa, a trait lacking in any pterosaurs.

Witton also prefers archosaurs as pterosaur sisters, and, in particular, Scleromochlus, despite the tiny hands that were, ironically, used to rule out Sharovipteryx. Evidently Witton prefers to have it both ways, so long as he stays within tradition. Witton lists fusion of the two proximal ankle bones to the shin (which does not occur in pterosaurs), reduction of the fibula (also in tritosaurs), the structure of the foot (actually more like that of tritosaur lizards like Cosesaurus, which retain an elongated pedal digit 5, which archosaurs lack), “several limb and hip proportions” (can Witton get even more vague here?) and the lack of bony scales along the back (then why is he ignoring those on Scleromochlus and Scutellosaurus).

Witton notes the shield-like pelves were different than in dinosaurs, but defends that by saying, “This may not be surprising, however, given, that pterosaur hindlinmbs were, uniquely among ornithodirans, used to support the wing in flight.” Utter rubbish!!! on the face of it and not pertinent to any phylogenetic discussion. You take the traits as they are and you let the computer decide where the taxa belong most parsimoniously. The “why” question or reason is never in play. By the way, similar pelves to pterosaurs can be found in fenestrasaurs, but these are ignored by Witton.

Witton writes, “arguments that basal pterosaurs were bipedal and digitigrade may be flawed” because basal ornithodires (aka: Asilisaurus, which bears no resemblance whatsoever to pterosaurs) were quadrupeds. This is far-reaching and totally bogus. I would be ashamed and would expect heavy chastisement having made such a comparison, especially after promoting bipedal Scleromochlus as a potential ancestor. But then Witton tops that bungle of reasoning by saying that Scleromochlus is “suspected of hopping about on plantigrade feet.” More fantasy! Few creatures, other than deer and horses, have feet more obviously digitigrade than Scleromochlus. Witton also ignores the known bipedal pterosaur footprints  (more here, here and more info here).

Page 21 Witton prefers an imagined hypothetical ancestor to a real one, and it glides from trees. Of course, this does nothing to explain the origin of flapping (because no gliders flap, unless they started off as flappers). Witton ascribes the mobility and length of the fifth toe to its use as a stabilizing tool, ignoring the fact that most tritosaurs from Tanystropheus to Sharovipteryx, have such a fifth toe, thus it cannot be developed for flight. Witton reports that the fifth toe, which is lateral, elongates to frame the medial membrane, which should strike you as odd and implausible. In reality the fifth toe is not connected to a membrane, except in Sharovipteryx, and each membrane trails each hind limb. They don’t cross to connect with each other.

Page 22 Witton reports that the hind limbs rotate out sideways to create efficient airfoils, but even that is fraught with error. One: Archosaurs can’t do this with their erect femurs. Two: Basal pterosaurs can’t do this either with their erect femurs. Raising the hind limbs to the horizon happens in later, more derived pterosaurs with a more sprawling femur.

Witton reports that during the evolution of pterosaurs that the fourth finger became so enlarged and unwieldy that it needed to be stowed away when grounded. We can all stow away our fingers by pressing them against our palms, but Witton ignores this. He also ignores the axial rotation of metacarpal 4 so that digit flexion puts digit 4 along the posterior rim of the hand, not the palmar side any longer. Witton reports ungual 4 was missing, since it was no longer necessary. We’ve seen so many several cases of ungual 4 present on pterosaurs that it needs to be considered universal.

Witton adds fibers to wing membranes as they need to be more sophisticated in their unsupported regions, ignoring that Cosesaurus had trailing fibers before it had wing membranes (Ellenberger 1993, Peters 2009).

With regard to flapping, our expert Dr. Witton reports, “At some point, manipulation of these wings in the vertical plane produced flapping, and self-propelled flight was achieved.” Gee, he makes it sound almost as if it was that easy. At ReptileEvolution.com and the PterosaurHeresies blog you learned the exact steps the exact taxa took to achieve flapping prior to the development of wings in pterosaurs, paralleling that same development in birds. So if Witton’s book leaves you unsatisfied and yearning for real answers, come see these websites and blogs.

Witton ascribes the development of flight muscles and bones to the ability of quadrupedal pterosaur ancestors to chiefly employ the forelimbs during leaps. He sort of leaves the larger hips and thighs out of the equation, evidently incapable of creating all the power necessary for a leap and leaving the unused arms in this bipedal model to do something else, like flap as a secondary sexual trait.

Dr. Witton does take the brave leap of including my published works in his reference list, something Dr. Unwin did not do in his less recent pterosaur book.

Let’s face it
If Dr. Witton does not even know what pterosaurs are (which he has acknowledged in his book), he has no business acting as an expert on pterosaurs and writing books about them. Unfortunately this is an acceptable trend continued by Dr. Unwin from Dr. Peter Wellnhofer. In chapter one Witton has already published too many errors. It’s too late in the game to fold ones’ hands and politely tell your readers, “Good question… we really don’t know. It’s one of the mysteries of paleontology.” There’s something called phylogenetic analysis that is guaranteed to give you an answer when you’re looking for an ancestor. However, you’ll have to include at least a few of the right taxa (among the tritosaurs in this case), to get close to the right answer. If you’re looking for the ancestors of pterosaurs, they’re right here in one place.

We’ll look at other Witton chapters in the future. But this one on pterosaur origins really irks me. It’s rather embarrassing that this sort of crap (a complete avoidance of certain data) is still being circulated. But I _do_ love the artwork.

References
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.

Cosesaurus pycnofibers, frills, membranes and hair

It is well known that pterosaurs were hairy
After all, Sordes is the “hairy devil.” The origin of pterosaur pycnofibers (ptero-hair) is the topic of this post. We covered the extradermal fibers on Sharovipteryx and Longisquama earlier here and here. Today we feature yet another hairy lizard and a sister to the ancestor of all three higher fenestrasaurs.

As reported earlier here and here, no one has done more work on the basal fenestrasaur, Cosesaurus aviceps than Dr. Paul Ellenberger (1993). Unfortunately Dr. Ellenberger’s bias towards birds blinded him to the pterosaur-like interpretations that would have revealed the prepubis, pteroid, quadrant-shaped coracoid and other pterosaur-like traits that he traced, but did not correctly interpret. On the other hand, Dr. Ellenberger did a good job of tracing the various extradermal membranes found around the sole specimen of Cosesaurus (Fig. 1). I use his illustration (Ellenberger 1993) to show that I am not the only one seeing these traces.

Figure 1. Cosesaurus fibers, frills and membranes. Here the same extradermal membranes found in Sharovipteryx, Longisquama and pterosaurs are found here. I’m using Ellenberger’s interpretation because mine are sometimes considered suspect.

Skull and Dorsal Fibers/Frills
A single row of fibers grading into frills tops the cranium and extends to at least the sacral area. These are homologous to the same structures in Huehuecuetzpalli, Macrocnemus, Iguana and Sphenodon. These structures reach an acme with Longisquama.

Tail Fibers
Ellenberger considered these the quills of primitive feathers. These fibers ultimately coalesce to become a tail vane in derived pterosaurs.

Arm Fibers
Posterior to the ulna are fibers that ultimately become a wing membrane in Longisquama and pterosaurs.

Leg Fibers
Anterior to the knee are fibers that are homologous to pycnofibers of pterosaurs. These are likely decorative and insular.

Uropatagia
Posterior to the legs are decorative frill/membranes that ultimately become the gliding membranes in Sharovipteryx, Longisquama and, to a lesser extent, in pterosaurs.

Not sure if we’ll find fibers prior to Cosesaurus. Its seems that Langobardisaurus has been too thoroughly prepared to ever know this and it has scales. Jesairosaurus does not preserve hairs and it was a lethargic type rather than a hyper-active taxon like Cosesaurus (remember the flap over flapping?).

In letters to a previous post, J. Headden questioned the identity of fiber-like shapes found in the neck skin of Sharovipteryx. With Cosesaurus having fibers and Longisquama having fibers and pterosaurs having fibers, phylogenetic bracketing (in spite of or in support of the fossil evidence) indicates that Sharovipteryx also had fibers.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Ellenberger P 1993. Cosesaurus aviceps. Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.

The rise and fall of the pterosaur tail – part 3

Earlier and yesterday we looked at parts 1 and 2 of the evolution of the pterosaur tail, the reduction of the caudofemoralis, the rotation of the chevrons (attenuation of the entire tail), the development of the tail vane and the appearance of caudal rods.

This series was inspired by a guest post by Scott Persons at Pterosaur.net.blospot on Jan 2.

Today we’ll finish up by looking at Dorygnathus, its ancestors, its variety and descendants (Fig. 1). Previously unrecognized for its importance, Dorygnathus lies at the center of all later pterosaur evolution.

Figure 1. The Dorygnathus clade and the pterosaurs AND their tails that descended from it.

The story of Dorygnathus tails begins with a small Eudimorphodon specimen, Bsp 1994. (Fig. 1) that had a tail of unknown length with small chevrons and no caudal rods.

Sordes was derived from a sister to it and had a relatively short tail with short caudal rods.

The many species within the genus Dorygnathus were larger and had a longer tail supported by caudal rods, supporting our earlier hypothesis that size was a major factor, along with phylogeny, in the ossification of caudal rods.

One Dorygnathus specimen, SMNS 50164, gave rise to azhdarchids and their kin starting with TM10341. It was tiny, the tail was shorter and not stiffened by caudal rods or elongated chevrons. From this point on, elongated caudals and caudal rods no longer appeared in pterosaurs in this lineage.

Another Dorygnathus, R156, lies at the base of the much smaller short-tailed Ctenochasma and kin. From this point on, elongated caudals and caudal rods no longer appeared in pterosaurs in this lineage.

Jianchangnathus preserves only a short portion of its gracile tail, but this taxon gave rise to Scaphognathus. Two specimens demonstrate a reduction in overall size and a reduction in the tail, but n110 shows that elongated caudal “threads” were present stiffening the tail. This clade gave rise to all later pterosaurs, (Pterodactylus, Germanodactylus and their descendants and kin) all of which had a short weak tail. Following Scaphognathus, elongated caudals and caudal rods no longer appeared in pterosaurs in this lineage.

Jianchangnathus also gave rise to a dead-end clade, the darwinopterids, all of which had a medium-length stiff tail, except Pterorhynchus (Fig. 1), which had an elongated tail with segmented vanes running along most of its length. Quite unique, so far as we know, given the general lack of soft tissue preservation.

So the story of caudal rod development was not a simple one. Not all basal pterosaurs ossified them. They do appear primarily in larger forms, but Scaphognathus n110 is the exception on that matter. Caudal rods are not associated with flight, but are associated with vane development and size. They add bulk to the tail, so cannot be weight-saving devices, contra traditional opinion.

And tail vanes act like arrow vanes or weather vanes, keeping the tip of the tail close to the parasaggital plane and in line with the airstream passively.  If a pterosaur wanted to turn it had to bank and to make a coordinated turn, that requires a rudder of spoilers in an airplane, a pterosaur could do all of that with just its wings, like a modern flying wing airplane.

Basal pterosaurs had such a thin-as-a-whisker tail that mass and balance were of little concern. Later large pterosaurs thickened the tail for their own romantic purposes. It may be no coincidence that head crests appeared about the time that long tails with vanes disappeared. That’s fashion for you. You’re either in or out.

Update: Notably, the metronome hypothesis places pterosaurs on the ground when they do “their thang” with their highly ossified tails. Notably, dromaeosaurids were grounded Archaeopteryx descendants. So, caudal supports in both cases were NOT for aerodynamics but terra-dynamics. (Contra Persons and Currie (2012) who reported, “the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.”

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References (published after posted)
Persons WS IV and Currie PJ 2012. Dragon Tails: Convergent Caudal Morphology in Winged Archosaurs. Acta Geologica Sinica – English Edition 86 (6): 1402–1412. DOI: 10.1111/1755-6724.12009. http://onlinelibrary.wiley.com/doi/10.1111/1755-6724.12009/abstract

The rise and fall of the pterosaur tail – part 2

Yesterday we looked at the attenuation of the pterosaur tail, from tritosaur and fenestrasaur precursors like Huehuecuetzpalli and Cosesaurus to the basal pterosaur, MPUM 6009. Today we’ll look at how that hyper-attenuated tail evolved within the Pterosauria. This series was inspired by a January 2 guest blog by Scott Persons at pterosaur-net.blogspot.com in which Persons compared the tail of Rhamphorhynchus to those of dromaeosaurid dinosaurs.

The large pterosaur tree indicates that basal pterosaurs evolvedin two basic directions, 1) toward the Austriadactylus, Raeticodactylus and Dimorphodontia, which led to the Anurognathidae and 2a) toward the Eudimorphodontia, which led toward  Campylognathoides and Rhamphorhynchus on the one hand, and 2b) toward Dorygnathus and the rest of the pterosaurs on the other.

Figure 1. Basal pterosaurs in the Austriadactylus/Dimorphodon line. The blue areas represent the extent of the tiny caudofemoralis. The blue arrow points to the reduced distal tail vertebrae in Peteinosaurus, a basal protoanurognathid. That’s really the only news from this clade.

The Austriadactylus/Dimorphodon lineage did not create caudal rods. The chevrons were aligned with each caudal centrum and extended the length of a single centrum. In some taxa a forward extension further lengthened each chevron. There is no vane preserved, but then no other soft tissues were preserved post-cranially. When more or less completely preserved, the tails in this clade were very long and attenuated, except when you get to Peteinosaurus, which terminates the tail with tiny bead-like vertebrae. This condition is the first stept to further reduction of all the tail vertebrae in anurognathids, convergent with the tail reduction in other derived pterosaurs.

Quick point: both tails associated with Dimorphodon are not found with Dimorphodon. They could belong to another sort of pterosaur from the same formation. Images are here and here. 1. Sedwick Museum, Cambridge J.61175,  of the Whinborne Collection. 2. Natural History Museum, London.  Specimen number 41349. Even so, the caudal rods are not developed as much as in Campylognathoides. 

The reduction of the tail in anurognathids reduces the amount of mass and its moment posteriorly. One would expect a similar loss anteriorly to keep things balanced. Either that, or the toes (while standing) and/or wings (while flying) had to move anteriorly a little. I haven’t seen it yet.

Figure 2. The tail of Eudimorphodontidae, including Campylognathoides and Rhamphorhynchus to scale. Here the convergent development of ossified caudal rods appear most strongly in the large taxa. The pattern is interrupted in small transitional taxa and reaches its acme in the largest Rhamhorhynchus. So size is key here. Larger size = thicker tail and more caudal rods.

Ossified intertwining caudal rods first develop in Campylognathoides, disappear in tiny transitional taxa, like Bellubrunnus, then reappear in Rhamphorhynchus and reach an acme of development in the largest known Rhamphorhynchus (Fig. 2). This suggests that caudal rods might have been present, but unossified when not apparent in smaller fossil pterosaurs. The data also demonstrates that both phylogeny and size determine the development of caudal rods. This clade has the best record of vane preservation, so caudal rods and vanes are correlated and sex may also have something to do with it, as described earlier.

Notably, the metronome hypothesis places pterosaurs on the ground when they do “their thang” with their highly ossified tails. Notably, dromaeosaurids were grounded Archaeopteryx descendants. So, caudal supports in both cases were NOT for aerodynamics but terra-dynamics. (Contra Persons and Currie (2012) who reported, “the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.”

Next Dorygnathus and the reduction of the tail in the rest of the pterosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References (published after posted)
Persons WS IV and Currie PJ 2012. Dragon Tails: Convergent Caudal Morphology in Winged Archosaurs. Acta Geologica Sinica – English Edition 86 (6): 1402–1412. DOI: 10.1111/1755-6724.12009. http://onlinelibrary.wiley.com/doi/10.1111/1755-6724.12009/abstract

The rise and fall of the pterosaur tail – part 1

A recent post at Pterosaur.Net (a guest post by Scott Persons) compared the tail of basal pterosaurs to velociraptors and it piqued my interest. Let’s take a look at the situation in phylogenetic terms and touch on topics overlooked earlier. This will be #1 in a short series of three or four.

Figure 1. The evolution of the pterosaur tail beginning with a basal lizard, Huehuecuetzpalli. Already small in Huehuecuetzpalli, the caudofemoralis is further reduced in derived fenestrasaurs as the anterior ilium develops to anchor larger anterior thigh muscles. BTW, you won’t find a better gradual accumulation of pterosaurian traits among archosaurs, no matter how many millions of years you look. Why this hasn’t been embraced can only be due to politics or religion.

Persons noted, “The caudal skeletons of these long-tailed pterosaurs (with the exceptions of the dimorphodontids and very primitive forms) are strikingly similar to that of Deinonychus. In the case of long-tailed pterosaurs, the function of the caudal rods has always seemed obvious. As flying animals, increased rigidity would have helped a tail to serve as a stabilizer or as a rudder.” Not sure I can agree with this.

No pterosaur tail vane acted as a rudder. This is an old paradigm that refuses to die. The rudder was a secondary sexual trait that developed only in pterosaurs with a really robust tail (we’ll see those in the coming days with hints below). Aerodynamically the rudder acted like an arrow vane, keeping the back end of the tail in line with the front end, rather than flopping to one side or the other causing imbalance problems. Moreover, vanes were not universal on basal pterosaurs.

Persons noted a different need for tail stiffening: against ventral bending along its length due to gravity — and all the better if just bone did the work. He remarked, “We can be certain (or about as certain as the fossil record ever permits) that, when the caudal rods of pterosaurs evolved, it was in the context of an aerial lifestyle.” Unfortunately, without a phylogenetic context Persons was speaking beyond his ken. The weight of the tail was already greatly reduced from Huehuecuetzpalli to Cosesaurus and already stiff, judging by the extreme rigidity and length of the in situ specimens of Huehuecuetzpalli Reynoso (1998). It only became stiffer and thinner by Sharovipteryx, a biped, where this attenuated structure balanced the forequarters, as in dinosaurs, but without the great weight, only great length.

Caudal rods actually developed in derived pterosaurs and in every case the tail developed into a more robust, and therfore weighty, structure than in their forebearers, who were already flying. So, caudal rods developed along with tail vanes to be sexy. Dozens of pterosaurs without caudal rods demonstrate their superfluous use in flying.

Not all long-tailed pterosaurs had a tail vane. It developed from stiff tail hairs bunched at the tip, slowly evolving to the vertical plane.

More to the point of this series, only a few long-tailed pterosaurs had intertwining caudal rods and none achieved the acme seen in Campylognathoides and Rhamphorhynchus (itself derived from Campylognathoides). We don’t see this intertwining in dimorphodontids, Sordes, Eudimorphodon and basal dorygnathids (which we’ll look at later). Derived Dorygnathus did have intertwined rods by convergence.

The extremely long tail of MPUM6009 was extremely straight without ossified caudal rods extending more than a centrum in length.

Persons made the point that several tails of dromaeosaurids were actually quite bendable, based on their in situ  positions. Other dromaeosauruid tails were not flexible, again based on their in situ preservation. Persons did not present any pterosaur tails preserved sinuously, but didn’t mention the reason: They don’t exist.

Update: Notably, the metronome hypothesis places pterosaurs on the ground when they do “their thang” with their highly ossified tails. Notably, dromaeosaurids were grounded Archaeopteryx descendants. So, caudal supports in both cases were NOT for aerodynamics but terra-dynamics. (Contra Persons and Currie (2012) who reported, “the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.”

More on this topic tomorrow.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References (published after posted)
Persons WS IV and Currie PJ 2012. Dragon Tails: Convergent Caudal Morphology in Winged Archosaurs. Acta Geologica Sinica – English Edition 86 (6): 1402–1412. DOI: 10.1111/1755-6724.12009. http://onlinelibrary.wiley.com/doi/10.1111/1755-6724.12009/abstract

The Origin of the Pterosaur Tail Vane

The pterosaur tail vane is found in only a few clades of long-tailed pterosaurs. Campylognathoides + Rhamphorhynchus have traditional vanes (Fig. 1). Other basal pterosaurs have fibers, I suppose similar to pycnofibres, emanating from the tail, often concentrated at the posterior tip, sometimes very similar to a vane. Pterorhynchus creates its own pattern with a series of vanes on the posterior tail.

Vane Usage
Traditional workers, like Marsh (1882) have suggested a steering usage for the tail vane. The heretical view was expressed by Peters (2002), “The tail vane on a pterosaur would have acted passively, like a weather vane, keeping the tail near the parasagittal plane in turns and during gusts of wind. It would have made a poor steering device compared to simple banking of the wings.” An hypothesis suggesting the vane’s use as a secondary sexual signal was blogged earlier.

Early and Recent Observations and Hypotheses on Tail Vanes
Marsh (1882) described the segments of the tail vane in Rhamphorynchus phyllurus as extensions of the neural spines and chevrons.

Dr. David Hone reported in his blog, “Structurally, all vanes have transverse banding across them which is presumably some form of reinforcement, though where the vanes are composed entirely of skin and interstitial tissues or have perhaps cartilage or anything else involved in their composition is not known.” 

Tail Hairs Expand and Coalesce to Form a Vane
The evolution and first appearance of a tail vane has not been covered in the literature. Figure 1 portrays select fenestrasaur and pterosaur taxa with tail hairs and tail vanes. It’s clear that one evolved from the other. Hairs can become cornified. Pangolin scales and rhinoceros horns are examples of this. Below are descriptions of several taxa that demonstrate the evolution of tail vanes from tail hairs (pycnofibres).

Figure 1. Pterosaur tail vane evolution. Click to enlarge.

Tail Hairs and Tail Vanes in Select Fenestrasaurs (including Pterosaurs)
Cosesaurus – Slender hairs, first identified as proto-feather divisions by Ellenberger (1978, 1993), emerge from the entire length of the tail.
Longisquama – Difficult to determine, but possible hairs gathered at the tail tip form a primitive decoration convergent with the vane of later pterosaurs.
Anurognathus – Tail hairs restricted to posterior half of the tail vestige.
Batrachognathus – Only a few longer hairs tip the vestigial tail.
Campylognathoides – The tail hairs coalesce to become a vertical tail vane that acts as a secondary sexual signal and passively reorients the tail tip in line with the flight path like feathers on an arrow.
Rhamphorhynchus intermedius – Phylogenetic size reduction included tail vane reduction.
Rhamphorhynchus (Vienna specimen) – The vane assumes a diamond shape.
Sordes – An atypical expansion of the distal tail bones including just a few tail hairs forming a vane shape, but not a vane.
Dorygnathus (Donau specimen) – The tail hairs coalesce at the tip but do not form a vane.
Dorygnathus SMNS 50164 – More substantial tail hairs indicated.
Pterorhynchus – Several dozen mini-vanes extend down the posterior half of the tail. These were individually expanded tail hairs.
Scaphognathus (Maxburg specimen) – An ephemeral trinagular tail vane may have been present. Subsequent taxa appear to reduce this.

Summary
Tail vanes in pterosaurs were most prominent in the Campylognathoides and Rhamphorhynchus clade. The evolved from tail hairs that first appeared in Cosesaurus. Tail vanes were reduced and disappeared in pterosaurs with a reduced tail.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Marsh 0C 1882. The wings of pterodactyles: American Journal of Science 23: 251-256.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.

Rhamphorhynchus Wing Tracings

Padian and Rayner (1993) published several soft tissue specimens of pterosaur wings. Here are several Rhamphorhynchus images along with color tracings to help delineate the elements.

Figure 1. The Zittel wing from a species of Rhamphorhynchus. Click to enlarge.

Figure 2. The Zittel wing tip. The green element could be a flipped ungual.

Figure 3. Rhamphorhynchus sp. BSP 1938 I 503a, No. 11 in Wellnhofer 1975 with wing membrane preservation. Here the wings are twisted such that the membrane is anterior to the digit. Even so, there is no deep chord aft of the elbows directed toward the ankles. Inserts enlarge wing tips which appear to include unguals.

Figure 4. Rhamphorhynchus YPM-1178. A wing tip was restored in plaster. Blue dots are aligned with joints in the wing.

Figure 5. Rhamphorhynchus BSP AS I 772 in which one wing membrane has been torn distally from the wing finger. There is no increased chord closer to the body. Lighter pink appears to be some sort of shift in the membrane impressing in the matrix before burial.

Figure 6. BSP-1937-I-37-588. The central portion is restored in plaster. The chord does not appreciably deepen proximally.

The Big Question Is: Did the Wing Membrane Extend to the Ankle?
Several workers (Bennett 2008; Elgin RA, Hone DWE and Frey E. 2011; Unwin DM and Bakhurina NN 1994) reported that pterosaurs had a deep chord wing membrane that extended to the ankles. We discussed this earlier. All purported samples presented by Elgin et al. (2011) were shown to be bogus. Peters (2002) found no clear connection has been made to the ankle in any pterosaur fossil as this further example also demonstrates. There’s also the example of the darkwing Rhamphorhynchus here. There is no gradual or steep deepening of the wing membrane in any of these specimens.

Membrane Shrinkage?
Elgin RA, Hone DWE and Frey E. (2011) considered the BSP 1938 I 503a specimen (Fig. 3) to be an example of “membrane shrinkage” trying to side-step the evidence for a narrow-chord membrane. There is no membrane shrinkage. There is only folding, ripping and mutilating during taphonomy in every sample above. Every example portrays the same wing shape, which is damn strong evidence that no pterosaur wings were attached to the ankle.

If anyone has ANY evidence of deep chord wing membrane, please bring it forward. I’d love to see it.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. 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 online pdf
Padian K and RaynerJV 1993. The wings of pterosaurs. American Journal of Science 239-A, 91–166.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

Tail-Assisted Pitch Control in Lizards (and Pterosaurs)

A recent paper entitled “Tail-assisted pitch control in lizards, robots and dinosaurs” (Libby et al. 2012) reported, “… lizards control the swing of their tails in a measured manner to redirect angular momentum from their bodies to their tails, stabilizing body attitude in the sagittal plane.” They also reported, “Our dynamics model revealed that a body swinging its tail experienced less rotation than a body with a rigid tail, a passively compliant tail or no tail.”

As in Dromaeosaurs
Libby et al. (2012) introduced their abstract with this statement, “In 1969, a palaeontologist proposed (Ostrom 1969) that theropod dinosaurs used their tails as dynamic stabilizers during rapid or irregular movements, contributing to their depiction as active and agile predators.” This hypothesis has been widely accepted. Archaeopteryx is an example of such a morphology.

Figure 1. Click to enlarge. Fenestrasaurs including Cosesaurus, Sharovipteryx, Longisquama and pterosaurs

Applicable to Fenestrasaurs and Pterosaurs?
The stiff attenuated tail of Cosesaurus, Sharovipteryx, Longisquama and basal pterosaurs bears strong similarities to the tail of Archaeopteryx and dromaeosaurs, especially so in derived long-tailed pterosaurs, like Rhamphorhynchus in which the various zygopophyses and chevrons elongated and intertwined with one another in much the same fashion leaving only the proximal caudals free to move. In birds the short tail and long tail feathers may flex dorsally and ventrally to enhance balance. The same seems to hold true for fenestrasaurs and pterosaurs (as lizards themselves). Both birds and fenestrsaurs largely reduced the caudofemoralis muscles and their bony caudal anchors diminishing the ability to swing the tail left and right.

The Arboreal Leaping Theory for the Origin of Pterosaurs
Bennett (1997) proposed a leaping behavior for the origin of pterosaurs. Bennett (1997) used hypothetical models. My studies with the increasingly long-legged and bipedal pterosaur ancestors Cosesaurus, Sharovipteryx, Longisquama and MPUM 6009 confirm a leaping origin, with the addition of bipedal digitigrade locomotion (reversed in several derived pterosaurs). Libby et al. (2012) tested lizard leaping in the laboratory replicating behaviors that these fenestrasaurs likely practiced in the Triassic wild.

Figure 2. Click to enlarge. The most primitive known pterosaur, the Milan specimen, MPUM 6009.

Elevating the Tail Permanently in Basal Pterosaurs
In lizards and derived pterosaurs the tail was held in line with the sacrum and dorsal vertebrae, but in Longisquama and basal pterosaurs (Fig. 2) the sacrum and posterior ilium was elevated distally, at right angles to the anterior ilium. This permanently elevated the base of the tail, similar enough to long-tailed lemurs and house cats. Despite the low mass of an attenuated fenestrasaur/pterosaur tail, elevation provided tail clearance from the substrate while standing with the shoulders elevated above the hips. It also moved the center of gravity anteriorly with dynamic possibilities (flight, with a center of balance at the shoulder joint). Thirdly a vane on the tail tip in derived long-tailed pterosaurs likely provided a secondary sexual signal, as blogged earlier.

Lowering the Tail Permanently in Derived Pterosaurs
Later pterosaurs reversed this early configuration, straightening out the posterior ilium and sacrum, perhaps as the proximal caudal vertebrae evolved more flexibility. An elevated tail would not have been as aerodynamic as an in-line tail so this was probably also a factor.

Figure 3. The Jayne lab documents bipedal locomotion in Callisaurus.

How Living Lizards Run Bipedally
The Bruce Jayne Lab in Cincinnati, Ohio, has produced a video of a zebra-tailed lizard (Callisaurus, Fig. 3) in fast quadrupedal and bipedal locomotion filmed on a treadmill. Note the horizontal configuration of the spine and tail, similar to the configuration reconstructed in Sharovipteryx. Compare this to the video of the basilisk (Jesus lizard) running more erect with an elevated tail, similar to the reconstruction of Longisquama (Fig. 1). Another living lizard, the Australian frilled lizard (Chlamydosaurus kingii, Fig. 4) also had an erect carriage when bipedal.

Fig. 4 Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. Image courtesy of R. Shine, published in Peters 2000.

A Dynamic Tail and Probable Behaviour Patterns in Fenestrasaurs
Sharovipteryx did not have much of an elevated posterior ilium and tail (Fig. 1), but Longisquama did. The difference appears to be related to stance and problems with tail/substrate clearing due to stance. Sharovipteryx had such long hind limbs that tail clearance was not an issue. The morphology of Longisquama, with its short neck, large grasping hands and strong leaping legs has been compared to modern long-tailed lemurs, which actively leap from tree to tree and cling to vertical tree trunks. Basal pterosaurs were also likely tree clingers judging by their ability to grasp medial columns with forelimbs otherwise unable to pronate and supinate.

The Reduction of the Long Tail in Derived Pterosaurs
According to cladistic analysis the reduction of the long, stiff tail in basal pterosaurs occurred by convergence three times: 1) after the proto-anurognathid MCSNB 8950; 2) after Dorygnathus (SMNS 50164); after Dorygnathus (Up R 156) and 3) after Scaphognathus (the Maxberg specimen) (Fig. 5). The last of these is the only one in which the tail demonstrates extreme reduction in length and depth. Most workers agree that subtle refinements and improvements in aerodynamic abilities elsewhere in the pterosaur anatomy reduced the need for dynamic stablization from a long, stiff tail.

Figure 5. These four small to tiny pterosaurs demonstrate tail reduction following taxa having a longer and more robust tail.

The Pattern of Tail Reduction in Pterosaurs
At some point the utility of an elongated tail diminished in pterosaurs, as it did in birds. Contra traditional stuides, tail reduction in pterosaurs appeared three times during overall size reduction in pterosaurs. Examples include the tiny Dorygnathus sisters TM 10341, St/Ei I and the tiny Scaphognathus sister, TM 13104 (Fig. 5). These reductions may be considered paedomorphic sequences in which the genes for tail lengthening and stiffening simply did not turn on as these three pterosaur clades retained embryonic traits (a flexible tail curled into a shell) earlier and earlier in their ontogenetic development.

The Pterodaustro Tail
The tail of derived pterosaurs has been rarely documented, but in Pterodaustro (Codorniu 2005) a comparatively elongated tail was present. Kellner and Tomida (2000) documented the tail of Anhanguera. Young (1964) documented the tail of Dsungaripterus. Zhenyuanopterus preserved a completely articulated tail. These were all substantial tails, yet still relative vestiges. Traditional views promote the disappearance of tails in pterodactyloid-grade pterosaurs. Not so, according to these derived examples.

The Pteranodon Tail
Bennett (1987 ) described an unusual tail attributed to Pteranodon that had duplex centra capable only of elevation and depression. This tail terminated in extended parallel rods, probably representing fused duplex centra. This tail was likely too small to affect aerodynamic abilities. If present on a female, such a tiny fragile tail might have been in danger of damage during mating. Perhaps it was capable of curling over the back to permit mating without damage, co-opting the tail-assisted pitch control of its nonvolant lizard ancestors.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bennett SC 1987.  New evidence on the tail of the pterosaur Pteranodon (Archosauria: Pterosauria). Pp. 18-23 in Currie, P. J. and E. H. Koster, eds. Fourth Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Occasional Papers of the Tyrrell Museum of Paleontology, #3
Bennett SC 1997. The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 123: 265–290.
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Codorniú LS 2005. Morfología caudal de Pterodaustro guinazui (Pterosauria: Ctenochasmatidae) del Cretácico de Argentina. Ameghiniana: 42 (2): versión On-line ISSN 1851-8044.
Libby T, Moore TY, Chang-Siu E, Li D, Cohen DJ, Jusufi A, Full RJ 2012. Tail-assisted pitch control in lizards, robots and dinosaurs. Nature. 2012 Jan 4;481(7380):181-4. doi: 10.1038/nature10710.
Ostrom JH 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bull. Peabody Mus. Nat. Hist. (Paris) 30, 68–80, 144. Young CC 1964. On a new pterosaurian from Sinkiang, China. Vertebrata PalAsiatica 8: 221-256.