New Paper on Pterosaur Pelves part 3

In part 1 of this post we reviewed a new paper on pterosaur pelves by Hyder et al. (2012). Yesterday we discussed part 2. Today we’ll finish.

Ornithocheiroidea
Hyder et al. (2012) include toothless, sword-jawed Pteranodon and Nyctosaurus with the toothy, spoon-tipped ornithocheirids. This is a mistake created by not including enough taxa as demonstrated by the large pterosaur family tree. Hyder et al. (2012) report, “The unfused scapulocoracoids and skull bones of these remains suggest they represent immature individuals, indicating that only the oldest ornithocheiroids have completely fused, imperforate pelves.” Actually these are all mature individuals. Lack of fusion in the sacral and pelvic elements are phylogenetic in pattern, not ontogenetic. The pelves of pteranodontids (closer to eopteranodontids and germanodactylids) bear little resemblance to those of ornithocheirds (closer to cycnorhamphids and scaphognathids), except for the Field Museum specimen of Nyctosaurus, which is the only specimen from this clade illustrated by Hyder et al. (2012).

Ctenochasmatoidea
Hyder et al. (2012) include pterodactylids, ctenochasmatids and cycnorhamphids in this clade, but the larger study separates these taxa widely. Here again, Hyder et al. (2012) stumble when they report, “Unfortunately, the majority of these specimens represent immature individuals (Bennett 1996).” Fusion follows phylogenetic pattern in pterosaurs. As lizards they don’t follow archosaur fusion and maturation rules, but may fuse early in ontogeny and keep growing, or they may never fuse certain bones, no matter how old they get (Maisano 2002). This reminds of the joke, “Where are all the baby pigeons? – Those ARE the babies.” It’s not a funny joke, it just came to mind.

Dsungaripteroidea
Hyder et al. (2012) correctly include germanodactylids  and dsungaripterids in this clade, but others (e.g. tapejarids, pteranodontids) were left out. The 3-D pelves in this clade are wonders to behold. Note that all fuse or meet ventrally. None of this open bottom baloney.

Azhdarchoidea
Hyder et al. (2012) incorrectly include azhdarchids and tapejarids in this clade. To their credit they report, “…adult remains of the tapejarid Sinopterus also seem to lack notaria and supraneural plates (e.g. Lü et al. 2006b), suggesting this group never attained neural spine fusion in their trunk region.” Supraneural plate development occurs occasionally in this clade by convergence, as in other large pterosaur specimens from other clades.

Functional Evolution of the Pterosaur Pelvis
Once again, Hyder et al. (2012) avoid discussing the origin of pterosaurian pelvic traits from plesiomorphic taxa, a subject covered by Peters (2000, 2002). Hyder et al. (2012) report, ichnological and biomechanical evidence indicates,”all pterosaurs were primarily plantigrade quadrupeds when walking and running.” This ignores recent literature on bipedal pterosaurs and fenestrasaurs featuring bipedal tracks. Hyder et al. (2012) report, “we follow hypotheses that all pterosaurs, including the earliest forms, held their legs in an erect stance.” This is correct for basal forms, but ignores derived pterosaurs in which the femoral head was more or less aligned with the femoral shaft, creating a very sprawling posture (Fig. 1).

Terrestrial locomotion in pterosaurs, two views.

Figure 1. Terrestrial pterosaurs – two configurations. Above the configuration promoted by Hyder et al. (2012). The short red arrows point to 1. an overextended elbow; 2. too large of a pes; and 3. femoral head not aligned with acetabular cup.  The long red arrow shows the power vector running from the hand to the shoulder. Note: it is braking the animal with every step, not contributing a forward vector during locomotion. Below, the configuration promoted here, in which the hind limbs provide all of the propulsion with the forelimbs merely acting to steady the animal. Note the center of balance remains beneath the shoulder glenoid when standing still. This changes with forward motion, as it does in humans who also lean forward when they walk. Ornithocheirids were not good walkers. Their spindly legs merely kept their rumpus off the tarmac.

Hyder et al. (2012) compare the proportions of the Dimorphodon pelvis and hind limb with those of Scleromochlus and dinosauromorphs, ignoring the morphological differences. They report, “pterosaurs were capable of bursts of speed,” but impeded by the uropatagia (uropatagium) stretching between the hind limbs. The hypothesis of a single uropatatium between the hind limbs is a false precept covered here. Hyder et al. (2012) support a bounding, hopping gait to work around this problem, but no pterosaur tracks show this. Could be. Might be. So far no evidence.

Lengthening of the Preacetabular Process
Hyder et al. (2012) report, “The broadening of the attachment site for epaxial musculature may reflect stiffening and strengthening of the torso, a trait that could be interpreted as a precursor to the development of supraneural plates over the pectoral and pelvic girdles in many forms.” Unfortunately this ignores the fact that Cosesaurus, expressing the genesis of this elongated ilium trait, had an otherwise tiny pelvis. Hyder et al. (2012) also report, “the elongate preacetabular process provides larger attachment sites or greater lengths for the hindlimb extensor muscles, thereby increasing their strength or endurance.” This is obvious. Hyder et al. (2012) report, “The condition of the preacetabular process does not seem to change relative to hindlimb morphology, which may suggest its development is largely independent of hindlimb mechanics.” Nothing could be further from the truth. Bones, muscles, they all interact.

Noteworthy, Hyder et al. (2012) completely ignore the great reduction in caudofemoralis anchors on the attenuated tail, largely without transverse processes or descending chevrons. The loss of posterior muscles and the enlargement of anterior muscles directed at the hind limb shift the center of balance forward and made possible flight, as in birds and, along a different path, bats.

Ornithocheiroid Pelves
Hyder et al. report, “The pelves of ornithocheiroids have undergone greater changes than in any other pterosaur group, presumably reflecting distinct hindlimb mechanics in this clade. The dorsal inclination of the preacetabular process is their most distinctive pelvic feature and would have been detrimental to leverage of the limb extensors.” Some of the problems they see are due to an incorrect reconstruction. It’s important to match the acetabular cup with the femoral head, to keep the prepubis between the femora, to keep the knees well bent and to keep the toes below the center of balance, below the armpits. Elevating the torso does this and Hyder et al. recognized this to their credit.

Azhdarchoid Pelves
By homology (according to Hyder et al.) and by convergence (according to the large pterosaur family tree) the pelves of tapejarids and azhdarchids developed a large, fan-shaped post-acetabular process.  Hyder et al. report, “it may represent a unique solution to increasing hindlimb retractor power among archosauriforms. Most archosauriforms use their robust tails to anchor a powerful, femur retracting M. caudofemoralis, but the slender pterosaur tail was unable to support such powerful musculature (Persons 2010). Instead, azhdarchoids appear to have increased the size and leverage of M. flexor tibialiis and M. iliofemoralis musculature, and may have given them larger, more superficially mammalian-like haunches, than reptilian.” Good point. However, the one thing both have in common is a large skull, sometimes crested, sometimes at the end of a long neck. In both cases additional opposite leverage would have been helpful and this may be why the post-acetabular process became expanded in these taxa. But really, who knows?

Why there’s something very wrong with our pterosaurs.
Giving credit where credit is due, the following pterosaur experts all had a hand in the report by Hyder et al. (2012) according to the acknowledgements: Darren Naish, Steve Vidovic, Dave Unwin, Dino Frey, Ross Elgin, Lorna Steel, Mike Habib, David Hone and Michael Benton. 

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
Hyder ES, Witton MP and Martill DM 201X. Evolution of the pterosaur pelvis. Acta Palaeontologica Polonica 5X (X): xxx-xxx. http://dx.doi.org/10.4202/app.2011.1109
Maisano JA 2002.
 Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrate Paleontology 22:268-275.

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9 thoughts on “New Paper on Pterosaur Pelves part 3

  1. I just want to say that, while it isn’t clear that “there’s something very wrong with our pterosaurs” as you contend, there’s definitely something wrong with the way you approach other people’s work. Even if you’re right about the things you discuss, you cannot keep saying that everyone else is incorrect about things when (a) you aren’t crediting the fact that most hypotheses in science are competing, and that we don’t really know what the “truth” is, and (b) it’s very clear that you are wrong, not those you’re criticising (example: of course Hyder et al. aren’t wrong in including azhdarchids within Azhdarchoidea).

    • To your point “a”: if you have competing hypotheses at odds with one another, as we do here, simple testing should reveal a winner from among the candidates. The losing candidate will produce untenable sisters with morphologies that could not have evolved from one another. The winner will have complete resolution echoing the natural order. We don’t really know what the “truth” is until we test it, as certain authors refuse to do. To your point “b”: There can be no clade, whatever name you give it, that includes only azhdarchidae and tapejaridae, other than one that extends much further back in time to include a host of other pterosaurs back to basal doryngnathids, according to the large pterosaur tree.

      • Then I wonder why your hypotheses isnt so popular. If like you say its about testing them to show their strength, then the fact that your works recieve so much ridicule and so little serious attention show that in fact, it is your theories that least echo the nutural order. All I see here is someone who enjoys trying to be contravertial for the sake of being so, who only gains his attention through pumping out as wild and wacky ideas as he can dream up. Excuse my poor spelling and grammar at the moment, your helping keep me entertained through a truly awesome cold.

      • Gaia,
        You’ll note the lower illustrations are mine, which match your suggestion to “bring them under the animal’. The upper ones belong to others. Indeed all four illustrations show quadrupedal locomotion, as most tracks now indicate and tracks matching those of Pterodactylus in particular. However, some bipedal tracks are known that you should become aware of. No one said the hind legs were weak. The long pelvis anchored a very large thigh muscle. The Anhanguera would not have been able to bring the hands in some due to its proportions. In this case simply raising the hands above the substrate would have enhanced travel, as in Nyctosaurus and Pteranodon, a method first proposed by Chris Bennett. Please review earlier posts of the Pterosaur Heresies to see animations, references and other evidence that may influence your view. Thanks for your note and take case of that flu.

  2. The elbows in the above set are only overextended because the wings are splayed too far forward. Bring them under the animal and there is no problem, and infact are far squatter then usually dedicated. Why on earth would they use their spindly little hind legs to provide propulsion and only use the powerfull forlimbs to steady themselves, when in fact it makes far more sence for them to just drop down on those forelimbs and have a much steadier quadropedal stance whare all four limbs served to move the animal? How would they become airbourn from a bipedal stance if the legs were so weak? In fact scratch ALL of this, there have allready been tracks of pterosaurs discovered SHOWING that they moved in a quadropedal fashion. The date of this article dosent lie right? 2012? Is this just a repost of an older article? Is my cold/flu causing me to hallucinate (judging by th look of some of those restorations, I’m considering that might be a yes)? I’m definately going to lurk this site some more, this is some pretty funny stuff.

  3. Ok, I promised myself that I wouldn’t post anything further here, but there’s something else that I really have to comment on. Toward the end of your article above, you include the subtitle ‘Why there’s something very wrong with our pterosaurs’, and you then list the people who were credited in the acknowledgments of Hyder et al. What I take from this is that you’re saying that Hyder et al. were wrong about everything because all those acknowledged people are wrong about everything as well. I find this perspective remarkably arrogant – even if you were right, it would be a very odd (and rude) thing to do. But the fact is you aren’t right: you know full well that the reason we reject your proposals, your hypotheses, your trees, and the observations that all of those things are based on is that you’re using a wholly unreliable technique that cannot be accepted as proper science. You need to stop thinking that everyone is against you because you are heretical. No, it’s because you’re mostly wrong.

    • That’s a pretty broad brush stroke, Darren. There is no arrogance here. As you know I give credit where credit is due. I also criticize those things that need criticism — and I do so with evidence. Your comments include no evidence. My results come from testing. I encourage you to test Huehuecuetzpalli in a pterosaur tree, to match tracks to trackmakers and to trace photographs of crushed fossils. What is unreliable about tracing photographs? Everyone does it. Photographs are a way to provide evidence to others. Wing membranes have been traced from photographs, but then described as “shrunken.” That’s cheating the evidence. What is unreliable about expanding your taxon list? Why do others refuse to expand their taxon list? It’s just a test! I appreciate your comment that I am “mostly wrong,” but seriously, you have to provide evidence on a point-by- basis (as I have) and you have to lose your fear of testing the opposing hypothesis (as I have).

  4. Lack of fusion in the sacral and pelvic elements are phylogenetic in pattern, not ontogenetic.

    Because the bones form as separate elements and fuse later, it’s ontogenetic in any case. The point in ontogeny at which they fuse is phylogenetic.

    The losing candidate will produce untenable sisters with morphologies that could not have evolved from one another.

    Once again: sister-groups don’t evolve from each other. They both evolve, independently, from a common ancestor. That’s why they’re called sister-groups.

    Wing membranes have been traced from photographs, but then described as “shrunken.” That’s cheating the evidence.

    You need taphonomic arguments for this. Remember that most fossils are fossils of rotting corpses, not of freshly died organisms.

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