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Pterosaur pubis retroversion – SVP abstract 2016

Friday, November 4, 2016 11:42
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(Before It's News)

RA Frigot 2016 
produced an abstract that appears to have no basis in reality. After reading the notes below, please send any examples of any pterosaur with a retroverted pubis, as noted in her abstract headline. I find no such examples in my fairly large collection of reconstructions.

From the Frigot 2016 abstract
“It has been demonstrated that the pelvis in archosaurs (1) repeatedly shows convergence towards acquisition of an anteriorly projecting ilium and a retroverted pubis. Pterosaurs have independently evolved these features, with the anterior iliac process universal across the taxon and the retroverted pubis occurring in several taxa (2). The latter cannot be appreciated as readily in pterosaurs as in other archosaurs due to the fused nature of the ischium and pubis (3). Geometric and linear morphometrics were used to quantify the shape and angle of the anterior margin of the pubis or puboischiadic plate. The angle and the PCA score were applied as end taxa to a reduced phylogenetic tree and nodes were reconstructed using least-squares parsimony. Retroversion is defined here as the anterior margin of the pubis subtending an angle of greater than 90° to the long axis of the spinal column (4).

“By examining the pubis, it can be seen that it becomes retroverted not once at the base of the Pterodactyloidea, as is consistent with existing hypotheses on gait, but in several different lineages independently. Due to the constraints of flight, it is unlikely that this retroversion accommodated a more massive gut, as is the consensus in Ornithischia and Therizinosauroidea. Retroversion has been associated with increased femoral retraction in Maniraptora, and a similar function of the retroverted pubis in pterosaurs is hypothesized here (5).”

“As the pubis becomes retroverted, the surface area caudad to the femur increases and surface area craniad to the acetabulum is reduced. Accordingly, moment arms of femoral protractors originating from the puboischiadic plate are reduced, and in some cases come to function as additional adductors. By contrast, the adductors are brought immediately ventral to the acetabulum, giving them greater mechanical advantage. This shape change is likely enabled by the expansion of the hip protractors onto the anteriorly expanded ilium. In terms of gait, a strongly retroverted pubis is unlikely to correspond to a vertical clinging style of arboreality, as the caudally rotated retractors are at an extreme mechanical disadvantage. This suggests either a terrestrial mode of locomotion, or a horizontal substrate arboreality (6). In addition, strong femoral retractors and adductors played a crucial role in developing and maintaining tension in the wing membrane (7), and in maintaining its planform and preventing collapse of the wing.”

Notes

  1. Pterosaurs have never been shown to be archosaurs without massive taxon exclusion. On the positive side, pterosaurs have been shown to be fenestrasaur tritosaur lepidosaurs in the large reptile tree which tests a wide gamut of taxa, including archosaurs.
  2. I have never seen a pterosaur with a retroverted pubis, but all have an anteriorly projecting ilium, starting earlier than stem facultative biped pterosaur taxa like Cosesaurus.
  3. Not all pterosaurs fuse the pubis and ischium. Many don’t.
  4. I just looked at several dozen reconstructions at ReptileEvolution.com and none of the pterosaurs has a pubis that extends more than 90º to the spinal column.
  5. Not sure we can talk about a special function here when there is no retroverted pubis in any pterosaur.
  6. Funny, no discussion of the prepubis here, which serves as an anteroventral (not posterovental) extension of the pubis and an anchor for femoral muscles on both vertical and horizontal surfaces. And it is present in all pterosaurs and non-pterosaur fenestrasaurs.
  7. Evidence says no. The pterosaur wing is stretched between the wingtip and elbow with a shallow fuselage fillet extending to mid thigh in all pterosaurs that preserve the wing membrane. There is still no evidence for a wingtip-to-tibia-or-ankle deep chord wing membrane in any pterosaur. If you have such evidence, please send it.

What am I not getting here?
This abstract doesn’t make sense. How did it pass peer review?

prepubes, prepubis

Figure 1. The pelvis and prepubis of several tritosaurs, fenestrasaurs and pterosaurs

References
Frigot RA 2016. Retroversion of the pubis in pterosauria and its significance in reconstructing gait. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

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