Two unlikely forelimb launching pterosaurs

Today we’ll look at two very different pterosaurs and wonder how it was even possible that these should be considered to be forelimb launchers.

The first is the basal pterosaur, MPUM 6009 (Fig. 1). It has the longest hind limbs compared to fore limbs. In these pterosaurs the hind limb leap alone would obviate the need for further spring off the forelimbs. Moreover, putting the short forelimbs on the substrate demands an awkward butt-high configuration unlikely to provide any sort of efficient launching. Phylogenetically all pterosaurs following this one had longer forelimbs capable of touching the substrate without losing balance over the toes.

MPUM 6009 with red and orange layers applied to show muscles. The hind limbs are well muscled, fully capable of leaping. The forelimbs are incapable of touching the ground without a very awkward butt-high configuration.

Figure 1. MPUM 6009 with red and orange layers applied to show muscles. The hind limbs are well muscled, fully capable of leaping. The forelimbs are incapable of touching the ground without a very awkward butt-high configuration.

Basal pterosaurs, derived from long-legged flapping fenestrasaurs like Longisquama, had longer hind limbs than forelimbs. This legacy of this hind limb leaping cannot be ignored.

 A completely different situation here with Nyctosaurus bonneri, in which the forelimbs are much longer than the hind limbs. Could those forelimb muscles provide a sufficient leap to clear the ground with those giant wing fingers before it comes crashing back to earth. Better to extend the wings while bipedal on those meaty thighs, then start flapping, running and leaping.

Figure 2. A completely different situation here with Nyctosaurus bonneri, in which the forelimbs are much longer than the hind limbs. Could those relatively small forelimb muscles provide a sufficient leap to clear those giant wing fingers before crashing back to earth? Better to extend the wings while bipedal on those meaty thighs, then start flapping, running and leaping, adding thrust with each wing flap.

When the forelimbs are much longer than the hind limbs
Nyctosaurus (Fig. 2) is the prime example of pterosaurs with the opposite morphology: longer forelimbs than hind limbs. Here it is hard to imagine this pterosaur becoming airborne without extending its wings for lift. The meaty thighs could have kept this pterosaur balanced over its toes while the wings unfolded. The meaty thighs could also have provided an initial leap or run to launch. Such large wings would have provided extra thrust, but only while extended. The triceps muscles appear to be pitifully too small to rapidly extend the forelimb to launch the pterosaur like a super pogo-stick.

Most other pterosaurs have a more balanced configuration with forelimbs and hind limbs more closely related in terms of length and the placement of joints. Even these were able to raise their forelimbs off the substrate to unfold the wings without losing balance over the toes.

Causes of the problem
Shortchanging the muscles of the pelvis, prepubis and femur by Witton (2013) and others is only one cause of their false paradigm. Creating poor reconstructions that disfigure real morphology is the second problem. Putting faith in imaginary ancestors with odd and improbable morphologies rather than verifiable fossil ancestors with real bones is the third cause.

That’s why I’m here, to encourage change based on evidence.

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