Quetzalcoatlus – Why so big? Why such a long neck?

Yesterday we looked at a bad YouTube video on the giant pterosaur, Quetzalcoatlus. Earlier we looked at the tiny predecessors, like No. 42, of mid-size to giant azhdarchids pterosaurs.Tiny taxa had roughly the same proportions and were formerly considered specimens of the unrelated Pterodactylus. Here, some thoughts on what made Q so big and with such a long neck.

This is where reconstructions really come in handy.
I made a rough model of Quetzalcoatlus based on Q. sp., took a photo, then manipulated the photo to various neck configurations (Figs. 1, 2). I added a fake water surface since ancestral taxa going back to No. 42 and Dorygnathus, were water waders and the lineage includes a flightless water wader, Sos 2428. It may be pertinent.

Quetzalcoatlus neck poses. Dipping, watching and displaying.

Figure 1. Quetzalcoatlus neck poses. Dipping, watching and displaying. Gray areas mark tendon soft tissue matching smaller long-necked pterosaurs. If height was important to Q for display, than raising the beak quickly and easily makes it appear even taller. This converges on similar behavior in certain modern stork-like birds. Simply having a tall neck provides a better survey of the environment, inherited from tiny predecessors, like n42 and n44. The long beak is necessary to reach the ground or lake bottom, where the food is. The neck is unable to bend ventrally. See figure 2 for the feeding posture.

Natural selection
Apparently some azhdarchids had greater mating success the taller they were. Females appear to have selected taller males. Taller ones were better able to spot enemies from greater distances and to threaten them back with a taller bluff-and-show on approach. Taller azhdarchids could also exploit deeper waters for food, temperature regulation and protection.

All this is well and good, but most pterosaur workers have tried to understand azhdarchids, like Quetzalcoatlus, from a feeding perspective.

Like vultures?
Azhdarchids were originally considered scavengers of dino carcasses (Lawson 1975) since Q. was discovered near dino bones.

Like sandpipers?
Langston (1981), who studied Q, thought azhdarchids fed on burrowing invertebrates by probing for them in the substrate. Such burrows were found near Q. fossils.

Like skimmers?
Nesov (1975) saw his Azhdarcho as a soaring skimmer. Unwin et al. (1997) agreed with this vision.

Like storks?
Paul (1987a) imagined Quetzalcoatlus, “probably patrolled water courses, like a three-meter-tall stork, picking up fish and small animals.” Padian (1988) agreed with the stok/heron-like image, but noted that Langston (1981) was probably correct. : – /

Like ground hornbills?
Witton and Naish (2008) agreed with the stork analog, but added ground hornbills and imagined that azhdarchids frequented terra firma due to the size of their feet (see below). Perhaps this is the paper that inspired the bad YouTube video featuring Q snapping up a baby T-rex because featured illustrations by M. Witton has Q fetching baby sauropods.

Feet too small to wade?
Witton and Naish (2008) noted that, “azhdarchid footprints show that their feet were relatively small, padded and slender, and thus not well suited for wading.” Unfortunately they overlooked the fact that storks, flamingoes, spoonbills, sandpipers and other waders are not known for their large wide feet. Nor did they consider the value of toe webbing. Nor did they quantify azhdarchid feet versus other pterosaur feet. I found the feet of Q sp. to be average is size for a pterosaur of its size. Among pterosaurs, Pterodaustro had large feet. Ornithocheirids had small feet. Azhdarchids had the long, closely bound metatarsals that fit azhdarchid-sized footprints along with toes that looked short by comparison to those long metatarsals.

Failing to divide azhdarchids from eopteranodontids
Unfortunately all prior authors failed to differentiate azhdarchids from their unrelated and convergent sisters, the eopteranodontids. Azhdarchids, derived from Dorygnathus and n42, among others, had flat beak tips, more like a spoonbill than a heron. Eopteranodontids, derived from Germanodactylus, had a tooth-tipped sharp beak, more like that of a heron than a spoonbill.  With flat, squared-off beak tips and small eyes, azhdarchids would have blindly felt for prey underwater. On the other hand, eopteranodontids used their large eyes to spot prey and their needle-sharp beaks to spear prey.

Quetzalcoatlus scraping bottom while standing in shallow water.

Figure 2. Quetzalcoatlus scraping bottom while standing in shallow water. Only a slight shift forward of the manus drops the front of the torso a little, which drops the long cantilevered neck and head deep enough so the beak can blindly scrape the bottom, here stirring up a little graphic mud. The neck would have been unable to descend any more than the straight line shown here. A series of tendons, preserved in other long-neck pterosaurs, supported the cervicals. 

Like geese and spoonbills?
Previously ignored, geese and spoonbills probably make better analogs for azhdarchids. These analogs are very close to the sandpiper hypothesis of Langston (1981, Fig. 2) in which food items are felt rather than seen and snapped up randomly rather than targeted and attacked. Azhdarchids had small eyes set far back on their skulls (Figs. 1, 2), not binocular and thus ill-suited for targeting prey. The flat bills would have been suitable for prey that did not fight back.

Breathing while probing?
In this pose (Fig. 2) it’s interesting to note that Q. could keep breathing while foraging with its long beak underwater, perhaps demonstrating one reason why the naris was greatly reduced to closed off completely in pterodactyloid-grade pterosaurs of many sorts.

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
Witton MP and Naish D 2008. A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271
Langston W Jr 1981. Pterosaurs. Scientific American 244: 92–102. online
Lawson DA 1975. Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science 187: 947-948.
Nessov LA 1984. Pterosaurs and birds of the Late Cretaceous of Central Asia. Paläontologische Zeitschrift 1: 47–57. online
Paul GS 1987. Pterodactyl habits – real and radio controlled. Nature 328: 481. online
Unwin DM, Bakuhrina NN, Lockley MG, Manabe M and Lü J 1997. Pterosaurs from Asia. Paleontological Society of Korea Special Publication 2: 43–65. online

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