When Pteranodon gets big, so do its wing bones, so it can keep flying

Earlier we looked at 
how the best known two dozen Pteranodon specimens can be readily split into about two dozen species. No two are alike and all can be lumped and split in a pterosaur cladogram. Contra traditional studies, no gender differences are apparent.

Size
As certain Pteranodon specimens grew larger and larger (Fig. 1) the arm bones, especially the antebrachium and metacarpal 4, became increasingly robust. This must have been a structural modification for keeping the largest specimens flying. Perhaps this is so because the weight increases more or less by the cube of the length… and the skulls + crests are getting larger, too.

Figure 1. Four Pteranodon specimens of increasing size. More robust arm bones are found in larger specimens. There is no reduction of distal wing elements.

Figure 1. Four Pteranodon specimens of increasing size. More robust arm bones are found in larger specimens. There is no reduction of distal wing elements in this volant genus.

Importantly,
the distal wing phalanges do not become vestiges in volant pterosaurs (Fig. 1) whether in the genus Pteranodon or the very large ornithocheirids.

Figure 1. Quetzalcoatlus specimens to scale.

Figure 2. Quetzalcoatlus specimens to scale with a former 6-foot-tall president. Note the slender antebrachium (radius + ulna) and vestigial distal wing phalanges.

This is distinct from
mid-sized to giant azhdarchids, which have vestigial distal wing phalanges (Fig. 2). This pattern of wing reduction follows the same pattern seen in much smaller flightless pre-azhdarchid like Jme-Sos 2428, the flightless anurognathid PIN 2585/4 and flightless nyctosaurs, like Alcione.

There is a clade of pterosaur paleontologists and artists
who are enamored with the idea of giant flying azhdarchids. They say the math is on their side, but they’re not looking at what small pterosaurs do when they become flightless (see above). Given the present data, the flightlessness of six-foot-tall azhdarchids enabled the next magnitude in size increase, just as the near flightlessness of larger tinamous, secretary birds and parrots enabled the next magnitude of size increase to create giant flightless ostriches, terror birds and Gastornis.

FIgure 2. A basal pteranodotid, the most complete Pteranodon, the largest Pteranodon skull matched to the largest Pteranodon post-crania compared to the stork Ciconia and the most complete and the largest Quetzalcoatlus

FIgure 2. A basal pteranodotid, the most complete Pteranodon, the largest Pteranodon skull matched to the largest Pteranodon post-crania compared to the stork Ciconia and the most complete and the largest Quetzalcoatlus

The largest flying birds,
like Pelagornis, have proportions similar to those seen in the largest flying ornithocheirids and pteranodontids. The largest flying azhdarchid-like, long-legged wading birds, the storks, cranes and shoebills, never get much taller than a human. All larger birds are flightless. All larger azhdarchids are also flightless, based on their reduced wingtips and narrow ante brachia, but still use their wings for thrust (Fig. 3).

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff. There was no longer any need for aerodynamic balance as a flightless sprinter, so the  neck were free to achieve giraffe-like proportions and size with a giant skull tipping the balance even further.


References

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