Question: Could the largest azhdarchids fly?
Tradition says: Yes! Most pterosaur workers say: Yes! Flying azhdarchid models say: Yes!
We looked at that question earlier and came to another conclusion based on comparable vestigial wingtip phalanges in flightless pterosaurs. Today there’s more to consider.
Let’s take another look at that same problem,
this time comparing the largest flying bird to the largest flying pterosaurs, and the largest non-flying bird to a giant pterosaur (Fig. 1). Since the largest flying birds and pterosaurs had the longest wing/neck and wing/torso ratios, the reduction of wing span/neck length points toward flightlessness—if analogous.
As reported yesterday,
lacking the ability to fly removes the constraints for multiple increases in size. We know of no pterosaurs that had vestigial wings, only vestigial distal wing phalanges. Three of the four flightless pterosaurs we looked at earlier were pterodactyloid-grade quadrupeds, so their free fingers had to contact the substrate. Moreover, all flightless pterosaurs could still flap vigorously, whether to ward off threats by display and/or increase thrust while fleeing.
While recognizing obvious differences
between the largest pterosaurs and birds, which are more alike?
On the one hand
we have pterosaurs and birds with shorter necks, shorter legs and longer wings.
On the other hand
we have a pterosaur and a bird with a longer neck, longer legs and a relatively shorter wing (compared to those of volant pterosaurs). Is it really as simple as that?
Or did I cherry-pick taxa?
Azhdarchids are often compared to storks.
And they do have similar proportions (Fig. 2). But all storks fly and some of the largest (e.g. Ciconia) are only half as tall as the smallest Quetzalcoatlus sp. We know of no giant storks. Even so, at half as tall, the legs of Ciconia were equal in length to the larger Q. sp, the torso was similar in size, and the neck and skull were only half as long. All this would appear to make azhdarchids top heavy relative to the volant stork (Fig. 3), despite a longer wing span, even with reduced distal elements.
What about those wings?
Compared to the stork, Q sp. had longer wings. Compared to albatrosses and pterosaurs, Q. sp. had shorter wings. In any case, that long neck is strikingly different in azhdarchids. Such a long lever arm had to affect the center of balance (Fig 3 red line).
What about that mechanical flying Q. sp?
Paul Macready built and flew a gliding Q. sp., (Fig. 4) not a Q. northropi. It did not have a long enough neck or large enough skull. As it was, it was well-engineered and all the mechanics in the torso were unlikely duplicated in the Late Cretaceous taxon.
The question(s) comes down to:
If large soaring birds are analogs to large flying pterosaurs, then are the largest non-flying birds analogs to the largest pterosaurs? Does giving up flight enable and promote gigantism in birds AND pterosaurs?
At present, the evidence says: yes.
However, it’s not that giant pterosaurs were “too big to fly”.
Here’s the working hypothesis: Smaller pterosaurs that stopped flying were then able to grow much bigger, with less constraint for maintaining a center of balance at the shoulders.
Not sure why it took so long
to put large pterosaurs and birds together. This should have been posted years ago.