Were early pterosaurs inept terrestrial locomotors?

Witton 2015 asked:
“Were early pterosaurs inept terrestrial locomotors?” Sorry, this online paper escaped my notice until now. It’s two years old.

The answer is
an unqualified “YES” when Witton turns perfectly good bipeds (supported by morphology, outgroups (Fig. 2), ichnites and omitted citations), into stumbling quadrupeds encumbered by imaginary wing membranes (Fig. 3) that connect the ankles and lateral pedal digits to the wing tips and binds the legs together with a single uropatagium. The Unwin influence is strong in those English youngsters. He also rotates the humerus in a shoulder joint that does not permit rotation (Fig. 1), which would be very bad for a flapping reptile, bird or bat.

Figure 1. Tracings from bones (on left) compared to Witton's freehand quads. Comments in red.

Figure 1. Tracings from bones (on left) compared to Witton’s freehand quads. Comments in red.

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.”

This may be true when you construct pterosaurs that don’t match footprints and you have no idea where ‘early pterosaurs’ came from, even though that has been known for 17 years. Obligate bipeds (Longisquama and Sharovipteryx) are outgroups. Basalmost pterosaur, Bergamodactylus (Fig. 2) , has longer hind limbs and shorter forelimbs (Fig. 2) than other pterosaurs, retaining these plesiomorphic traits.

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Figure 2. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus. Does this look like a quadruped to anyone? All derived pterosaurs have relatively shorter legs. Outgroups, whether the invalid Scleromochlus, or the valid Sharovipteryx, have long legs like these. Uropatagia are not preserved, but they are on a related taxa one node away, Sharovipteryx. Note the tail is NOT incorporated.

Witton’s abstract continues
“This is commonly justified by the absence of a non-pterodactyloid footprint record,”

(False, see Peters 2011)

“suggestions that the expansive uropatagia common to early pterosaurs”

(False, misinterpretation of Sordes)

“would restrict hindlimb motion in walking or running, and the presence of sprawling forelimbs in some species.”

(sprawling at the top, narrow gauge on the substrate (Fig. 3).

“Here, these arguments are re-visited and mostly found problematic. 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.”

Or possibly by grasping branches and tree trunks, but even that possibility is not considered or argued against by Witton.

Getting back to the uropatagium found in bats…
primitive bats extend a membrane from both legs back to the tail. Only in the most derived bats, like Desmodus (Fig. 3), is the tail a vestige to absent. The resulting uropatagium without the tail extends between the legs – while completely avoiding the toes. Thus the pterosaur/bat analog, is also bogus. Final point: basal bats don’t walk or run on their hind limbs. They hang. Only in bats like the vampire do some bats reacquire the ability to actively hop around on horizontal surfaces, like cow buttocks and grassy knolls.

Witton carefully avoids
any mention of papers in which bipedal pterosaur trackways are described (Peters 2011). He fully supports the uropatagium hypothesis proposed by Sharov 1971 and further supported by Unwin and Bakhurina 1994 (disputed by Peters 2002 and here). That uropatagium, found in no other specimens of Sordes or any other pterosaur, is really a displaced wing membrane (Figs. 3–5) along with a displaced radius and ulna as shown here. Note: a few days ago Witton’s latest illustration used pedal digit 5 to frame both the uropatagium and the brachiopatagium. No one else does this. No argument or explanation is given.

Figure 6. Above, from Witton 2017 focusing on the pterosaur uropatagium. Note: even though fanciful, it does not incorporate the tail, but goes from leg to leg, UNLIKE Desmodus the bat, which incorporates what little tail is left.

Figure 3. Above, from Witton 2017 focusing on the pterosaur uropatagium. Note: even though fanciful, it does not incorporate the tail, but goes from leg to leg, UNLIKE Desmodus the bat, which incorporates what little tail is left. Besides, their is NO homology here. Witton is trying to support a bad interpretation with a bad analogy. Not a good idea to support an analogy with invalid drawings. Witton gives no support through testing to the uropatagium controversy, but accepts it with blinders on.

Witton carefully avoids
any mention of other candidate pterosaur outgroups, like fenestrasaurs (Fig. 2), and the assistance they can offer to the questions posed, but supports the basal bipedal crocodylomorph, Scleromochlus, as a potential outgroup. Ironic, isn’t it?

My first question would be, which outgroup taxon has anything resembling a leg-spanning uropatagium?Certainly not phytosaurs. Nor any archosaur. Sharovipteryx has separate uropatagia, but in Witton’s world view those are not the same, nor are they to be mentioned, because that would involve citing some academic paper from Peters, which would be antithetical to Witton’s premise. In good science, all counterarguments are considered, attacked or supported.

The myth of the pterosaur uropatagium

Figure 4. The Sordes uropatagium is actually displaced wing material carried between the ankles by the displaced radius and ulna.

Witton supports
the invalid shrinkage hypothesis of Elgin, Hone and Frey (2011) to explain away narrow-chord wing membranes preserved in the fossil record…which would be ALL of them

The hind limbs and soft tissues of Sordes.

Figure 5. The hind limbs and soft tissues of Sordes. Above, color-coded areas. Below the insitu fossil. Note how insubstantial the illusory uropataigum is compared to the drawing that solidifies the area. Tsk.Tsk.

Witton reports,
“Trackways made by running pterodactyloids indirectly demonstrate how elastic their proximal membranes must have been, allowing track makers to take strides of considerable magnitude (Mazin et al., 2003) despite membranes stretching from the distal hindlimb to their hands (Elgin, Hone & Frey, 2011).” The other explanation is that the wings and hind limbs were always decoupled (as documented in all known fossils). Pterosaurs do not have a membrane extending to the ankles. Witton proposes a bounding gait for pterosaurs, even though no pterosaur tracks document this.

Figure 7. A plesiomorphic bat with the tail incorporated in the uropatagium. This bat, Myotis, cannot walk very well. Desmodus, highly derived, has required the ability to walk, but at the expense of its tail and a vestige uropatagium.

Figure 6. A plesiomorphic bat with the tail incorporated in the uropatagium. This bat, Myotis, cannot walk very well. Desmodus, highly derived, has required the ability to walk, but at the expense of its tail leaving a vestige uropatagium. Everything must be put into a phylogenetic context, even in analogies.

Thankfully Witton supports
“Assessments of pterosaur hindlimb muscle mechanics seem to confirm that the pterosaur pelvic and femoral musculoskeletal system is optimally configured for an erect stance.” 

But then he puts the fingers on the ground (Fig. 1). Why???

Perhaps Witton does not realize
what happens to his uropatagium when the pes is plantigrade, which is how Witton always reconstructs pterosaur pedes. Somehow he avoids drawing the lateral digit reversed toward the pelvis, as he proposed earlier.

Witton has no criticism
for one of his references, Hone and Benton 2007 (but did not cite the setup 2007 paper. Readers know, for many reasons, this is one of the worst papers ever published in this field. The facts will stun even freshmen paleontologists. 

Witton ignores the pterosaur sacrum,
which has more than the typical two sacrals found in a wide range of quadrupedal reptiles. Why does the pterosaur sacrum add and fuse vertebrae phylogenetically and more with larger taxa? For the same reason that humans, apes and theropod dinosaurs do. They are bipedal and the sacrum acts as the fulcrum to a long lever arm.

Earlier we talked about pterosaur workers wearing blinders, ignoring papers with hypotheses that conflicted with pet hypotheses. Now you see that happening in real time.

When workers, like Witton, stopped citing papers
I had published in academic journals is when I took my evidence and arguments online.

Earlier, in a multipart critique,
here, here, here, here and here we talked about Witton’s previously published work combined in a single book. I only wish someone with influence on Witton and his collaborators would remind them that their ideas and papers are going to end up like the Victorian-age cartoons they mock – unless they get back to facts and evidence.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeonntologica Polonica 56(1): 99-111.
Peters D 2002. 
A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277–301.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Witton MP 2015. Were early pterosaurs inept terrestrial locomotors? PeerJ 3:e1018 DOI 10.7717/peerj.1018

5 thoughts on “Were early pterosaurs inept terrestrial locomotors?

  1. Great post, David! Some of your reconstructions sure make more sense then the usual ones. (Traditional) Anurognathus’ huge eyes and flat face always bothered me.
    But, your idea of isometric growth on a reptile still confuses me. Pardon my ignorance, but there are any exemples of this trait in living species, or even in the fossil record of proximal outgroups for pterosaurs?

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