Pterosaur pubis retroversion – SVP abstract 2016

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.

Advertisements

Basal hominid, fenestrasaur and archosaur analogies

When you look at the transition
from quadrupedal locomotion to bipedal locomotion in early hominids (Fig. 1), among many other details, you can’t help but be impressed by the increase in the relative length of the hind limbs.

Figure 1. When hominids became bipedal, their hind limbs became longer.

Figure 1. When hominids became bipedal, their hind limbs became much longer.

The same can be said
for the transition from semi-bipedal Cosesaurus (based on matching Rotodactylus tracks) to the fully bipedal Sharovipteryx (Fig. 2).

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration, analogous to hominids.

As in hominids,
freeing the fore limbs from terrestrial locomotion enabled fenestrasaurs to do something else, like flapping for secondary sexual displays, adding motion to their morphological ornaments. While the forelimbs were relatively smaller in Sharovipteryx, they were relatively larger in Bergamodactylus (Fig. 3) a long-legged basal pterosaur. There were no constraints on forelimb evolution in fenestrasaurs, analogous to theropod dinosaurs that ultimately became birds. Some theropods and birds grew larger forelimbs, while others reduced their forelimbs.

Figure 2. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus.

Figure 3. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus.

Lest we not forget
in the basal archosaurs (crocs + dinos) early attempts at bipedal locomotion (Fig. 3) also corresponded to a longer hind limb length in bipedal Scleromochlus and Pseudhesperosuchus as opposed to their common ancestor, a sister to short-legged Gracilisuchus.

Figure 3. Short-legged Gracilisuchus, along with sisters, long-legged bipedal Pseudhesperosuchus and Scleromochlus.

Figure 3. Short-legged Gracilisuchus, along with sisters, long-legged bipedal Pseudhesperosuchus and Scleromochlus.

Based on those tiny hands,
the forelimbs of Scleromochlus were becoming vestiges. Based on the long proximal carpals of Pseudhesperosuchus, the manus was occasionally lowered to the ground, perhaps while feeding. The origin of bipedal locomotion in basal crocs is the same as in pre-dinosaurs.

It took much longer and proceeded more indirectly
for bipedal archosaurs to start flapping their forelimbs, giving them a new use that ultimately produced thrust and lift as bird forelimbs continued to evolve and become larger.

See videos produced by ReptileEvolution.com
on the origin of dinosaurs here, on the origin of humans here, and on the origin of pterosaurs here.

A sign of beauty and/or Olympic potential
is a long-legged model or athlete.

More on Sinopterus liui

Yesterday we looked at a new specimen (IVPP V14188) attributed to Sinopterus liui by Meng (2015). Today we’ll take a closer look at the pectoral girdle, pelvic girdle and pes.

Figure 1. Sinopterus liui pectoral region with bones colorized using DGS. Note the sternal cristospine (lavender) has apparently broken off from the sternal shield. This is a dorsal view, but look at figure 2.

Figure 1. Sinopterus liui pectoral region with bones colorized using DGS. Note the sternal cristospine (lavender) has apparently broken off from the sternal shield. This is a dorsal view, but look at figure 2.

Sometimes its just easier
to see the bones when they are colorized. Many paleontologists use this technique. I’d like to see the method used more often.

Figure 2. Sinopterus liui pelvic region and hind limb colorized and reconstructed using DGS. While the pectoral region is exposed in dorsal view, the placement of metatarsal 1 on top here indicates a ventral view. The fibula is underneath the tibia here. We're also seeing the ventral distal femur.

Figure 2. Sinopterus liui pelvic region and hind limb colorized and reconstructed using DGS. While the pectoral region is exposed in dorsal view, the placement of metatarsal 1 on top here indicates a ventral view. The fibula is underneath the tibia here. We’re also seeing the ventral distal femur.

With just a few more parts accurately traced
this specimen can be added to a phylogenetic analysis to see where it nests.

References
Meng X 2015. A New Species of Sinopterus from Jehol Biota and Reconstraction of Stratigraphic Sequence of the Jiufotang Formation. A Thesis for the Master Degree of Science in the Graduate School of Chinese Academy of Sciences, directed by Wang X-L. (in Chinese)

Pterosaur worker puts on blinders

Sorry to have to report this, but… 
Witton (2015) decided that certain published literature (data and hypotheses listed below) germane to his plantigrade, quadrupedal, basal pterosaur conclusions, should be omitted from consideration and omitted from his references.

Everyone knows, iI’s always good practice
to consider all the pertinent literature. And if a particular observation or hypothesis runs counter to your argument, as it does in this case, your job is to man up and chop it down with facts and data. That could have been done, but wasn’t. Instead, Witton put on his blinders and pretended competing literature did not exist. Unfortunately that’s a solution that is condoned by several pterosaur workers of Witon’s generation.

Not the first time inconvenient data
has been omitted from a pterosaur paper. Hone and Benton (2007, 2008) did the same for their look into pterosaur origins after their own typos cleared their way to delete from their second paper one of the two competing candidate hypotheses.

Witton (2013) and Unwin (2005) did the much the same by omitting published papers from their reference lists that they didn’t like.

Publication
is a great time to show colleagues that you have repeated all competing observations and experiments and either you support or refute them. To pretend competing theories don’t exist just increases controversy and reduces respect.

So, what’s this new Witton paper all about?

From the Witton abstract: Pterodactyloid pterosaurs are widely interpreted as terrestrially competent, erect-limbed quadrupeds, but the terrestrial capabilities of non-pterodactyloids are largely thought to have been poor (false). This is commonly justified by the absence of a non-pterodactyloid footprint record (false according to Peters 2011), suggestions that the expansive uropatagia common to early pterosaurs would restrict hindlimb motion in walking or running (false), and the presence of sprawling forelimbs in some species (not pertinent if bipedal).

“Here, these arguments are re-visited and mostly found problematic. Restriction of limb mobility is not a problem faced by extant animals with extensive fight membranes, including species which routinely utilize terrestrial locomotion. The absence of non-pterodactyloid footprints is not necessarily tied to functional or biomechanical constraints. As with other fully terrestrial clades with poor ichnological records, biases in behaviour, preservation, sampling and interpretation likely contribute to the deficit of early pterosaur ichnites. Suggestions that non-pterodactyloids have slender, mechanically weak limbs are demonstrably countered by the proportionally long and robust limbs of many Triassic and Jurassic species. Novel assessments of pterosaur forelimb anatomies conflict with notions that all non-pterodactyloids were obligated to sprawling forelimb postures. Sprawling forelimbs seem appropriate for species with ventrally-restricted glenoid articulations (seemingly occurring in rhamphorhynchines and campylognathoidids). However, some early pterosaurs, such as Dimorphodon macronyx and wukongopterids, have glenoid arthrologies which are not ventrally restricted, and their distal humeri resemble those of pterodactyloids. It seems fully erect forelimb stances were possible in these pterosaurs, and may be probable given proposed correlation between pterodactyloid-like distal humeral morphology and forces incurred through erect forelimb postures. Further indications of terrestrial habits include antungual sesamoids, which occur in the manus and pes anatomy of many early pterosaur species, and only occur elsewhere in terrestrial reptiles, possibly developing through frequent interactions of large claws with firm substrates. It is argued that characteristics possibly associated with terrestrially are deeply nested within Pterosauria and not restricted to Pterodactyloidea as previously thought, and that pterodactyloid-like levels of terrestrial competency may have been possible in at least some early pterosaurs.”

Bottom Line: Unfortunately Witton paid little attention to
the literature on non-pterodactyloid ichnites and feet. And he ignored certain basic tenets.

Witton writes: “Given that likely pterosaur outgroups such as dinosauromorphs and Scleromochlus bore strong, erect limbs (e.g.,Sereno, 1991; Benton, 1999), it is possible that these early pterosaurs retained characteristics of efficient terrestriality from immediate pterosaur ancestors.”

Wrong as this ‘given’ supposition is, both of the above taxa (dinos and scleros) are bipedal, yet Witton refuses to consider this configuration in basal pterosaurs (for which he claims have no ichnite record).

Figure 1. Witton's errors with a quadrupedal Preondactylus. For a study on terrestrially, there is little effort devoted to the feet of pterosaurs here.

Figure 1. Witton’s errors with a quadrupedal Preondactylus. For a study on terrestrially, there is little effort devoted to the feet of pterosaurs here. Click to enlarge.

Digitigrady vs. plantigrady
Pterosaur feet come in many shape and sizes. Some have appressed metatarsals. Others spread the metacarpals. These differences were omitted by Witton. Some have a very long pedal digit 5. Others have a short digit 5. These differences were also omitted. Some pterosaurs were quadrupeds (but not like Witton imagines them), others were bipeds (Figs. 1-6). Basal pterosaurs had a butt-joint metatarsi-phalangeal joint, but that just elevates the proximal phalanges, as confirmed in matching ichnites.

Figure 2. Witton's quadrupedal Dimorphodon.

Figure 2. Witton’s quadrupedal Dimorphodon. Click to enlarge.

The quadrupedal hypothesis is a good one,
but it really only works in short-clawed plantigrade clades that made quadrupedal tracks on a horizontal substrate. Otherwise a quadrupedal configuration works only on vertical surfaces, like tree trunks, where the trenchant manual claws can dig into the bark. This was omitted by Witton.

Figure 3. Dimorphdon toes and fingers. Here, in color, I added the keratinous sheath over the claws that show how ridiculous it would be for Dimorphodon to  grind these into the ground. Better to use those on a vertical tree trunk.

Figure 3. Dimorphdon toes and fingers. Here, in color, I added the keratinous sheath over the claws that show how ridiculous it would be for Dimorphodon to grind these into the ground. Better to use those on a vertical tree trunk (figure 2). Click to enlarge.

Quadrupedal pterosaurs can’t perch
on narrow branches. Peters (2000) showed how a long pedal digit 5 acted like a universal wrench for perching.

Figure 1. Anurognathus  by Witton along with an Anurognathus pes and various anurognathid ichnites.

Figure 4. Anurognathus by Witton along with an Anurognathus pes and various digitigrade anurognathid ichnites, all ignored by Witton. Digit 5 behind the others is the dead giveaway.

Quadrupedal pterosaurs can’t open their wings
whenever they want to, for display or flapping. Witton favors the forelimb launch hypothesis for pterosaurs of all sizes, forgetting that size matters.

Figure 5. Quadrupedal Rhamphorhynchus by Witton (below) with errors noted and compared to bipedal alternative.

Figure 5. Quadrupedal Rhamphorhynchus by Witton (below) with errors noted and compared to bipedal alternative.

Pterosaurs were built for speed
whether on the ground or in the air. They were never ‘awkward.’ Remember basal forms have appressed metatarsals, they have more than five sacrals, their ichnites are digitigrade, the tibia is longer than the femur, the bones are hollow, when bipedal the feet plant below the center of balance at the wing root, and some pterodactyloid tracks are bipedal.

Figure 6. Quadrupedal Campylognathoides by Witton (center) with errors noted and compared to bipedal alternatives.

Figure 6. Quadrupedal Campylognathoides by Witton (center) with errors noted and compared to bipedal alternatives. The lack of accuracy in Witton’s work borders on cartoonish.

Accuracy trumped by imagination
By the present evidence, Witton has not put in the effort to create accurate and precise pterosaur reconstructions. Rather his work borders on the cartoonish and I suspect the reconstructions have been free-handed with missing or enigmatic parts replaced with parts from other pterosaurs. That should be unacceptable, but currently such shortcuts are considered acceptable by Witton’s generation of pterosaur workers.

The Sordes uropatagium false paradigm gets a free pass
and no critical assessment from Witton. (So far this uropatagium has been observed only in one specimen, Sordes (in which a single uropatagium Witton believes was stretched between the two hind limbs), was shown to be an illusion caused by bone and membrane dislocation during taphonomy. All other pterosaurs and their predecessors have twin uropatagia that do not encumber the hind limbs. The dark-wing Rhamphorhynchus (Fig. 5) is an example of a basal pterosaur with twin uropatagia.

References
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Peters D. 1995. Wing shape in pterosaurs. Nature 374, 315-316.
Peters D. 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41
Peters D. 2000b. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336.
Peters, D. 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Peters, D. 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Peters, D. 2009. A Reinterpretation of Pteroid Articulation in Pterosaurs – Short Communication. Journal of Vertebrate Paleontology 29(4):1327–1330, December 2009
Peters, D. 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters, D. 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141.
Peters, D. 2010-2015. http://www.reptileevolution.com
Unwin DM 2005. The Pterosaurs: From Deep Time. Pi Press, New York.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.
Witton MP 2015.Were early pterosaurs inept terrestrial loco motors? PeerJ 3:e1018<
doi: https://dx.doi.org/10.7717/peerj.1018

Anhanguera pelvic girdle and femur orientation

A recent paper
by Costa et al. (2014) illustrated the myology of the pelvic girdle of the large pterosaur, Anhanguera based on 3D digital models of 3D fossils (Fig. 1).

Figure 1. Costa et al. reconstruction of Anhanguera pelvis and femur together with amended versions with sprawling femur.

Figure 1. Costa et al. reconstruction of Anhanguera pelvis and femur together with amended versions with sprawling femur. Not sure how the rest of the body was oriented based on the Costa et al. pelvis. Here the pelvis is placed on a body that is balanced whether the hands are on the substrate or not.

Unfortunately,
Costa et al. did not include the rest of the Anhanguera body and leg to show their orientation and configuration works in toto. When you do the add the body, and orient the femur so the axis of the femoral head (Fig. 2) aligns with the axis of the pelvic acetabulum, you get a different configuration (Fig. 1). In the Costa et al. configuration, the femoral head axis is not aligned with the acetabulum axis. And the knee is a little too straight, unlike most tetrapods — except at maximum extension.

Fig. 2. Anhanguera left femur from Kellner and Tomida 2000. Note the axis of the femoral head is not far off from the axis of the femoral body, producing a sprawling hind limb here as it does in other tetrapods.

Fig. 2. Anhanguera left femur from Kellner and Tomida 2000. Note the axis of the femoral head is not far off from the axis of the femoral body, producing a sprawling hind limb here as it does in other tetrapods.

If you straighten out the leg, you get the flying configuration. 

If you bend the knee and axially rotate the femur, you get the standing configuration, just like lizards capable of assuming or running in a bipedal configuration (Fig. 3). Now I’m not saying Anhanguera was bipedal all the time — but it was indeed bipedal moments before takeoff and moments after landing (prior to wing folding, as in all pterosaurs.)

 

Bipedal lizard video marker

Figure 3. Click to play video. Just how fast can quadrupedal/bipedal lizards run? This video documents 11 meters/second in a Callisaurus at the Bruce Jayne lab.

Getting back to the feet, legs and pelvis
pterosaurs could still bring their feet close to the midline simply by bending the knee and axially rotating the femur, both of which were very easy to do.

Yes, Anhanguera might have been awkward on land,  but it was rarely on land, based on the evidence of the tiny feet, skinny legs and great big wings.

For those interested,
I just spent the last 6 months working on a reptile paper that was yesterday submitted. Hope it flies. Will try to add some new “heresies” as the days go by, but there has not been that much to discuss in the last few months, oddly enough.

And thank you for your support while I’ve been gone.
Viewership has not decreased. 200 to 400 visitors a day over the past month with no news! Amazing.

References
Costa FB, Rocha-Barbosa O and Kellner AWA 2014. Myological reconstruction of the pelvic girdle of Anhanguera piscator (Pterosauria: Pterodactyloidea) using three-dimensional virtual animation.

 

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.

Computational models of two pterosaurs from Hone and Henderson 2013. Note how both have trouble keeping their nose out of the water. Henderson's models have shown their limitations in earlier papers.

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.

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.

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.

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.

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 ones, like small pterosaurs, take advantage of surface tension to ride high while spread-eagle on the surface.

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.

Bennett Moves Pterosaurs to the Base of the Archosauriformes

Earlier we looked at Bennett (2012) in which he shifted pterosaurs back to the more primitive lumbering and aquatic archosauriforms Proterosuchus and Erythrosuchus (Fig. 1). That moved the former nesting away from dinosaursScleromochlus, Proterochampsids and Parasuchians, the previous archosaur ‘favorite candidates,’ which we earlier considered “strange bedfellows.”

It’s worth reiterating
With the same title and publisher, Bennett (2013) reports from his abridged abstract: “A previous analysis of the phylogenetic position of the Pterosauria argued that pterosaurs were not closely related to dinosaurs as is generally accepted, but rather were outside the crown group Archosauria. However, that study was dismissed for the use of inappropriate methods. Here, the data set from that analysis was divided into five partitions: […] Lastly, the data set was updated with additional characters and taxa from recent analyses, tested as before, and when analysed, suggested that the Pterosauria were basal archosauriforms well outside the crown group Archosauria (Fig. 1).

Figure 1. From Bennett 2012 in which he mixes lepidosaurormorpha (in blue) with euarchosauriformes  (in yellow) and pararchosauriforms (in pink). Nearly every sister in this "stone soup" is a strange bedfellow if you think about it.

Figure 1. From Bennett 2012 in which he mixes lepidosaurormorpha (in blue) with euarchosauriformes (in yellow) and pararchosauriforms (in pink). Nearly every sister in this “stone soup” is a strange bedfellow if you think about it. Anurognathus and kin are basal pterosaurs, though Anurognathus is Late Jurassic, so there are other problems here too, other than the use of suprageneric taxa.

Earlier I noted that when pterosaurs are stripped of their closest kin among the Tritosauria / Fenestrasauria down to and including Huehuecuetzpalli, they do indeed nest with Proterosuchus. 

That is what Bennett (2012, 2013) did,
then further examined the various partitions (one with characters associated with cursorial digitigrade bipedal locomotion, and the other four with characters from the skull and mandible, postcranial axial skeleton, forelimb, and hindlimb), for incongruence. This doesn’t help one bit when you ignore the only series of taxa with a gradual accumulation of pterosaurian traits, the tritosaur fenestrasaurs.

Bennett’s use of suprageneric taxa is also a problem.

And really, Proterosuchus??
Is that the best candidate the opposite team can muster?? I think this is yet one more case of experts casting a blind eye toward the subject of pterosaur origins.

References
Bennett SC 2012. The phylogenetic position of the Pterosauria within the Archosauromorpha re-examined. Historical Biology. iFirst article, 2012, 1–19.
Bennett SC 2013. The phylogenetic position of the Pterosauria within the Archosauromorpha re-examined. Historical Biology 25(5-6): 545-563.