Flight has evolved at least four times in the history of life. Flying insects evolved first, appearing in the fossil record about 350 million years ago. Pterosaurs came next, living for an impressive stretch of 160 million years of the Mesozoic Era. Birds actually evolved while pterosaurs were alive, though birds have outlasted their reptilian competitors. Bats are the most recent group to take to the sky, with the oldest fossils yet discovered at 52.5 million years old.
Of these fliers, pterosaurs are the only group with no living representatives today. Though pterosaurs are related to dinosaurs, they were not dinosaurs themselves. They were reptiles, but very different from the reptiles around today. For one thing, flying is a lifestyle that requires a lot of energy to sustain. To have a high enough metabolism to fly, pterosaurs were almost certainly warm-blooded, or endothermic. Adding even more support to pterosaurs being endothermic is the presence of fur-like pycnofibres on many pterosaur fossils. Fur doesn’t have many aerodynamic properties so the fur was probably used for insulation, giving pterosaurs protection against heat loss.
Early pterosaurs tended to be small, with long tails and a full set of teeth. Pterosaur diversity had a sharp increase in the early Cretaceous. During this time, some pterosaur species evolved fanciful bony crests. Their snouts diversified too, some becoming elongated and toothless beaks, others becoming adapted for straining small organisms from water, and some developing high arched keels.
In the Cretaceous, pterosaurs occupied all sorts of lifestyles and niches. Some of the most amazing of the pterosaurs were the azhdarchids. Azhdarchids had long necks, long beaks, long legs, and very small torsos. The smaller azhdarchid species still had formidable wingspans of about 9 feet. The biggest azhdarchids are the largest flying animals ever discovered. Quetzalcoatlus northropi had a wingspan of 33 – 36 feet, and other azhdarchid species were almost as big.
Their wings must have been powerful to lift such a large animal into the air, but they weren’t just used for flying. Trackways show that pterosaurs had a four-legged gait. There’s been a lot of discussion about the lifestyle of these soaring giants, and scientists have come to some surprising conclusions.
Throughout the years, some scientists have suggested that azhdarchid pterosaurs like Quetzalcoatlus were skim feeders, flying low over the water and snatching up hapless fish and squid that strayed too close to the surface. Others have suggested that the long beak of Quetzalcoatlus might be better suited for probing mudflats for prey. These days, the tides of scientific evidence are turning.
Paleontologists like Mark Witton and Darren Naish studied azhdarchid trackways, limb proportions, and body shape to better understand how these pterosaurs might have lived. What they discovered shed fascinating new light on azhdarchid lifestyles. These massive predators didn’t roam the swamps or dive into the ocean, they were swift striders of the land, hunting on foot on solid ground. With their erect posture, long limbs, and long necks, they must have looked like strange reptilian giraffes, giraffes that could take to the air when faced by predators, and were fierce predators themselves.
This lifestyle is called “terrestrial stalking,” and azhdarchids stalked prey in both wooded and open environments. Though large, they were light on their feet and wouldn’t have had any problem moving through trees. They were probably fairly flexible in their diet and could have eaten carrion, small animals, and maybe even fruits or other plant parts.
Some azhdarchids shared their ecosystems with large predatory theropod dinosaurs, but that doesn’t mean they were on the menu. Azhdarchids were big. The larger ones had shoulder heights of around 8 feet and their heads were held high at around 13 feet. With powerful beaks that were over 3 feet long, they would have made a daunting meal for other carnivores. Other azhdarchid species lived in ecosystems containing only smaller predatory dinosaurs. In these places, azhdarchids could have been apex predators themselves!
Azhdarchids were certainly formidable beasts. They could hunt on the ground, were strong fliers, and depending who you ask, might have been able to predate on humans if we lived at the same time. The closest modern analog to azhdarchid pterosaurs are large birds that forage on foot, like the Marabou Stork, but clearly azhdarchids were in a league all of their own.
- Kate Dzikiewicz, Paul Griswold Howes fellow