Pterosaur corner

I recall an anecdote related by David Attenborough about a celebrity reception that he once attended one evening after he had been filming for a sequence on the aerodynamics of pterodactyls. A venerable and obviously well connected lady engaged him in conversation, and asked him what he had been doing recently. “Actually, today I was flying a pterodactyl”. To which the old lady retorted, “Yes, they are so graceful, aren’t they”. They do have a large following, perhaps second only to dinosaurs, and three interesting items came to my attention in the last couple of weeks.

One of the known pterosaur groups is the Tapejaridae, comprising small to medium-sized pterosaurs with wingspans up to 4 m. They are quite spectacular in appearance, having large crests relative to their overall size. Their fossils have turned up in Cretaceous sediments in South America, Europe and China, and a new find in Morocco (Afrotapejara zouhrii) extends their range to Africa (Martill, D.M. et al. 2020. A new tapejarid (Pterosauria, Azhdarchoidea) from the mid-Cretaceous Kem Kem beds of Takmout, southern Morocco. Cretaceous Research. V. 112: onlin, 104424; DOI: 10.1016/j.cretres.2020.104424). See also: De Lazaro, E. 2020. New species of pterosaur discovered in Morocco (Sci News, 6 April)

Also reported in Cretaceous Research are three new species of toothed, fish-eating pterosaurs of the ornithocheirid group. They too come from the Cretacous Kem Kem beds of Morocco, and again adding Africa to the range of the genera to which they belong. Even the largest flying animals known to science have emerged from the same strata. These are the azhdarchid pterosaurs, the largest of which had a wing span of more than 9 metres and stood at the height of a giraffe when on the ground.

See: Anderson, N, 2020. New pterosaur fossils unearthed in Morocco (Sci News, 26 March)

Being so widely spread, these pterosaur group’s mode of flight must have been extremely efficient, perhaps even matching that of today’s albatrosses, which use turbulence over ocean waves to glide effortlessly, indeed the epitome of graceful travel. How they achieved such vast ranges is partly due to their extremely light-weight bones that were paper thin but strong because they contained vesicles filled with gas, much like the expanded polystyrene used in model pterosaurs of the kind flown by ‘Whispering Dave’ as Sir David Attenborough is fondly known. Their bone structures are similar, in this respect, to those of modern birds.

launch of Hatzegopteryx
Reconstruction of the giant pterosaur Hatzegopteryx launching into the air, just after the forelimbs have left the ground (credit: Mark Witton)

So, how did these graceful beasts fly? Like those of bats, pterosaurs’ wings were membranes, but rather than being supported by five elongated digits, as in bats, those of pterosaurs extended from their bodies to a single elongated ‘finger’ or digit: hence their old name pterodactyl, translated from the Greek as ‘wing finger’. For a long while, it was believed that pterosaurs had to live on high ground, even cliffs, in order to launch themselves in the manner of a hang glider. Reconstructions of their gait on the ground generally look extremely ungainly: they walked on their ‘wrists’ and the other three, small ‘fingers’ of their forelimbs.. How they probably launched themselves emerges from a detailed paper linking natural flight modes of birds, bats and pterosaurs to conceivable developments in aeronautics inspired by them (Martin-Silverstone, E. et al. 2020. Volant fossil vertebrates: potential for bioinspired flight technology. Trends in Ecology and Evolution, v. 35, in press 9 April 2020; DOI: 10.1016/j.tree.2020.03.005). The authors point to the great strength of the membrane structure itself, conferred by its three-layered structure, and to the aerodynamic properties of the wing. They conclude that, whereas pterosaurs were probably incapable of high-speed flight, they were extremely efficient at low speeds, ideal for soaring and for low-speed landing that would not endanger their fragile bodies. Simply by springing into the air using all four limbs they could attain sustained flight, although the largest of them were close to the limit. The necessary muscles actually made up about 40% of their body mass. See a reconstruction of the launch of the largest pterosaur, Quetzalcoatlus from the Late Cretaceous of North America

See also: Fossil Flyers Hold Secrets to Better Flight Technologies (Sci News, 18 April)