How could the larger pterosaurs support their giraffe necks?

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Scans of fossilized remains suggest that long-necked pterosaurs could support the weight of their heads – and secondarily that of their prey – thanks to an assembly of rays inside their vertebrae.

If you had lived in the Cretaceous period, you would have been able to see them without difficulty. You just had to roll your eyes. The Azhdarchidae, a family of pterosaurs, were distinguished by their large heads and extremely long necks, sometimes measuring over three meters. The most famous of them are none other than Quetzalcoatlus and Hatzegopteryx, two giants of more than twelve meters in wingspan as high as giraffes when placed on the ground.

The extreme dimensions of the Azhdarchidae naturally raise some interesting questions: How could they grab and transport large prey without breaking their necks? Or how could animals the size of giraffes soar effortlessly above the dinosaurs moving on the ground?

Cariad Williams, a doctoral candidate at the University of Illinois, hoped to shed light on these questions by drawing on a specimen found in the fossil deposits of Kem Kem, Morocco. Moroccan fossil beds here preserve a lush river system that existed around 100 million years ago. Ms Williams and her colleagues tentatively identified their specimen as a pterosaur of the genus Alanqa.

An artist’s rendering of a pterosaur. Credits Williams et al., IScience

Unheard of in the animal kingdom

Using a scanner, the researchers therefore focused on the animal’s neck. The results of this work, published Wednesday in the journal iScience, stunned them. And for good reason, the neck of the pterosaur was scaffolded by a unique and complex network of helical struts connecting a central neural tube to the vertebra wall like the spokes of a bicycle. This structure, in concrete terms, has no equivalent in the animal kingdom.

Biomechanical analysis of the complex neck structure revealed that the ray-shaped filaments strengthen the vertebrae against the pressures associated with capturing and transporting heavy prey. This specimen, which had a neck of 1.5 meters long for a wingspan of six to eight meters, wings spread, could have carried loads of more than ten kilos.

Below: uAn end-to-end CT scan of a fossilized pterosaur vertebra, revealing the ray-like structures formed within.

This unprecedented insight helps fill in some of the lingering gaps in our knowledge of pterosaur anatomy and, by extension, their behaviors. Like birds, these reptiles have indeed developed light and fragile skeletons to optimize their flight capacities. This is why they tend to be under-represented in the fossil record: their bones break easily.

According to the authors, this unusual adaptation could probably have other functions, such as the “nod”, a rivalry behavior observed in male giraffes, or as a means of coping with the shear forces associated with large. skulls shaken by high winds during flight.

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