An Obligate Bipedal Basal Pterosaur

The Traditional View
All pterosaurs were quadrupedal, based on trackway evidence.

MPUM 6009, the Milan specimen, the most primitive known pterosaur

Figure 1. The most primitive known pterosaur, the Milan specimen, MPUM 6009. The long hind limbs and relatively short fore limbs were homologous with those in Sharovipteryx and Longisquama. The extremely slender tail is most like that of Sharovipteryx, not later pterosaurs which thickened the tail with elongated chevrons and zygapophyses. Gray tones represent possible soft tissues, homologous with those in Cosesaurus and Longisquama.

The Heretical View
One basal pterosaur, MPUM 6009 (Wild 1978), was an obligate biped, retaining the long-legged morphology of its ancestral sisters, Sharovipteryx and Longisquama. All pterosaurs following MPUM 6009 (such as Raeticodactylus and Eudimorphodon) had shorter hind limbs and longer forelimbs, a combination that enabled quadrupedal locomotion.

MPUM 6009 was considered a small Carniadactylus by Dalla Vecchia (2009), but the differences are many.

MPUM 6009 in situ.

Figure 2. MPUM 6009 in situ. Click to enlarge and portray the Wild (1978) interpretation. Bones, impressions of bones and some soft tissue complete this articulated skeleton at the very base of the Pterosauria. The crushed skull required reconstruction. Here, using the DGS method, the bones have been colorized. This permits subtle impressions to be identified. Sister taxa share many of these traits, confirming their identity.

Longer Legs, Shorter Forelimbs
Here the reconstruction tells the tale. Question is, is the reconstruction accurate? The clues are, admittedly ephemeral, yet even without such long legs, MPUM 6009 nests at the base of the Pterosauria. So long legs are not beyond the realm of possibility. The relatively short neck allies this basal pterosaur with Longisquama, the outgroup sister taxon. The laterally increasing toe length and deep pelvis also ally this taxon with Longisquama. The sternal complex is also essentially identical.

Such long legs and short forelimbs “ally” this pterosaur with Scleromochlus, and basal dinosaurs, but — really, seriously — hardly at all. It’s convergence!! So if anyone from the traditional camp wants to bitch about this reconstruction, think twice. You’ll only be shooting yourself in the foot. Things happen when the forelimbs are elevated off the substrate, as we humans all can attest.

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.

How Living Lizards Run Bipedally
The Bruce Jayne Lab in Cincinnati, Ohio, has produced a video of a zebra-tailed lizard (Callisaurus) in fast quadrupedal and bipedal locomotion filmed on a treadmill. When the fore limbs are elevated the hind limbs go digitigrade. The speed is an incredible 11 meters per second.

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.

Dalla Vecchia FM 2009. Anatomy and systematics of the pterosaur Carniadactylus (gen. n.)rosenfeldi (Dalla Vecchia, 1995). Rivista Italiana de Paleontologia e Stratigrafia 115 (2): 159-188.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.


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