Earlier Pterodactylus, a small pterodactylid pterosaur, was animated to match Craysaac tracks (Fig. 1). In this model the backbone is elevated higher here than in some of the wireframe pterosaurs you may have seen (Fig. 3) and the forelimbs carry little if any of the weight. Nevertheless, in this species they work like and impress like ski poles — doing the pterosaur walk.
Today, Zhejiangopterus (Cai and Wei 1994), a large azhdarchid pterosaurs, is similarly animated to match large Korean pterosaur tracks (Hwang et al. 2002; Fig. 2).
Note how Zhejiangopterus carries its head, with the middle ear region above the center of gravity, like a human. At any point Zhejiangopterus could lower its skull for a meal or a drink. It could also raise its wings without shifting its balance to initiate a bipedal takeoff. Note how little the forelimbs actually touch the substrate. Again, this is the ski-pole hypothesis in which the forelimbs are used mainly to steady the pterosaur, not to generate thrust or support the weight (exception noted below).
The troubles with the horizontal backbone model are at least threefold
- The skull would be far from the center of gravity at the end of a long neck. Bearable, perhaps, in tiny Pterodactylus. unwieldy on giant Zhejiangopterus with its oversized skull.
- The forelimbs would bear most of the weight with the skull far beyond them. This is fine when floating and poling.
- Standing up to open the wings for display or flight would involve throwing the skull backward to end up standing bipedally. Awkward. Time consuming. The competing quad launch hypothesis is out of the question as reported earlier here and elsewhere for the reasons listed therein.
Mazin et al. (2009) published a series of imagined wireframe pterosaurs matched to the tracks (Fig 3). This is odd because a former champion of bipedal pterosaurs was co-author Kevin Padian, who was a quad ptero-track denier for many years until the Craysaac tracks won him over (while continuing to deny the pterosaur nature of other tracks. Odder still because the animation that was used for the public (which I saw year ago and not sure if it is still in use, but is not used here) showed a more upright Pterodactylus.
Note: The published wire frame model might match the gait and placement of the ptero tracks, but the manus and pes of the wireframe model are but a small fraction of the size of the tracks. This is something the authors and their referees missed, or overlooked. But we all know, the devil is in the details.
“If the glove doesn’t fit, you must acquit.” — Johnny Cochran at the OJ Simpson murder trial.
And if the feet and hands don’t match,
you’ve got the wrong wire frame pterosaur model. Contra Mazin et al., I took the effort to match the manus and pes track to an extinct taxon. In Science, you must use the data as precisely as you can, and let those data tell you, as closely as possible, how to build your model. Don’t walk in with your pet hypothesis and try to shoehorn or BS your way through it, unless you can get away with it, as Mazin et al. did until now.
If my model of pterosaur walking is correct,
and I’m sure it has minor flaws that may never be known, then the tiny manus bears nearly the entire weight of the pterosaur at one and only one brief point in the step cycle (Fig. 4) that does not need support in normal bipedal walking. The tiny area of the tiny fingers is likely to impress deeper because the weight of the pterosaur is concentrated on a smaller area (compared to the long foot) in contact with the substrate. This pose also might answer Mike Habib’s original mystery as to why the pterosaur humerus was built stronger than it needed to be for flight. Birds don’t put their weight on the forelimbs. And few bats do (the tiny vampire is the exception).
Here are the alternative models
for pterosaur quadrupedal standing (Fig. 5) for ready comparison. Which of these provides a bended knee with the proper vectors for thrust? The manus doesn’t have to and didn’t provide thrust, but it should not have been placed so far forward that it could only provide a braking vector to the shoulder.
On the other hand, a feeding pterosaur in water might have looked something like this (Fig. 6).
Cai Z and Wei F 1994. On a new pterosaur (Zhejiangopterus linhaiensis gen. et sp. nov.) from Upper Cretaceous in Linhai, Zhejiang, China.” Vertebrata Palasiatica, 32: 181-194.
Hwang K-G, Huh M, Lockley MG, Unwin DM and Wright JL 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geology Magazine 139(4): 421-435.
Mazin J-M, Jean-Paul Billon-Bruyat J-P and Padian K 2009. First record of a pterosaur landing trackway. Proceedings of The Royal Society 276:3881–3886.
Unwin D and Lü J. 1997. On Zhejiangopterus and the relationships of Pterodactyloid Pterosaurs, Historical Biology, 12: 200.