A Bipedal AND Quadrupedal Pterosaur Trackway

There has been a lot of completely unnecessary trashing of the possibility of bipedal pterosaurs. Almost everywhere you look, professional pterosaur paleontologists are insisting that pterosaurs could never walk bipedally because “all” pterosaur tracks demonstrate that the manus also made impressions.

The exceptions say otherwise (Fig. 1). Earlier we discussed bipedal pterosaurs herehere, here and here.

Figure 1. Pteraichnus nipponensis, a pterosaur manus and pes trackway, matched to n23, ?Pterodactylus kochi (the holotype), a basal Germanodactylus.

Figure 1. Pteraichnus nipponensis, a pterosaur manus and pes trackway, matched to n23, Pterodactylus? kochi (the holotype), a basal Germanodactylus.

Pteraichnus nipponensis (Lee et al. 2010) is one of the best examples of pterosaur trackways anywhere. Six trackways crisscross on a slab. All demonstrate quadrupedal locomotion, with the hands making impressions along with the feet. Trackway B, however, lead off with three bipedal steps, unattended by manus imprints.

It’s not difficult for pterosaurs to shift from one mode to the other. If you match tracks to trackmakers (which is easier than most pterosaur specialists think because virtually all pterosaur trackmakers had distinctive and unique feet and hands (Peters 2011). Pteraichnus nipponensis is closest in size and morphology to the holotype of ?Pterodactylus kochi, (no. 23 in the Wellnhofer 1970 catalog), a basal germanodactylid.

By simply lifting the hands off the substrate, pterosaurs could walk bipedally (Fig. 1). When they did implant their hands, they used their forelimbs more like ski poles than other tetrapods used their forelimbs. The forelimbs were incapable of providing thrust because the hands never moved behind the shoulders and elbows. Most pterosaur experts lean their reconstructions way to far forward, making no attempt at matching tracks to locomotion cycles. This has to be corrected.

Pteraichnus nipponensis is also unique in having fingers 1 and 3 diametrically opposed to one another (Fig. 1). Earlier we looked at this situation as one more proof that pterosaurs were lizards, not archosaurs. Lizards have looser finger joints that enable rotation. Archosaurs have never demonstrated this ability.

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
Lee YN, Azuma Y, Lee H-J, Shibata M, Lu J 2009. The first pterosaur trackways from Japan. Cretaceous Research 31, 263–267.
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

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