Quetzalcoatlus, genus made up of two species of giant pterosaurs classified in the family Azhdarchidae, which contains some of the largest known flying animals. Both species lived during the Maastrichtian Age (72.1 million to 66 million years ago) of the Cretaceous Period. One of them, Quetzalcoatlus northropi, is widely believed to have been the largest flying creature that ever lived. Q. northropi is known from a single set of fossils representing six individuals. Those fossils were found in the Javelina Formation of Big Bend National Park in Texas in the early 1970s and were first described in 1975. The other species, Q. lawsoni, is known from roughly 300 bone fragments representing a number of smaller individuals discovered at the same time and location, but the species was not described until 2021. Quetzalcoatlus is named for Quetzalcóatl, a wrathful Aztec deity who at times was represented as a feathered serpent (see also Aztec religion).

　　Size and habits Paleontologists contend that Q. northropi stood about 5 meters (16 feet) tall and had a wingspan of up to 11 meters (36 feet). Estimates of the pterosaur’s weight remain elusive, but it could have been as much as 250 kg (550 pounds), according to some researchers. Q. lawsoni was substantially smaller, but it still had a large wingspan, perhaps measuring 4.5–6 meters (15–20 feet). Like other pterosaurs, Quetzalcoatlus had no feathers. Instead, its body was covered with hair. (Despite their capacity for flight, pterosaurs are not ancestors of modern birds.) Quetzalcoatlus does not appear to have had a tail. It did, however, have a long neck—in Q. northropi up to 3 meters (10 feet) long—which supported a massive crested head of roughly the same size.

　　Quetzalcoatlus had a long jaw with no teeth, and it likely used its jaw to probe for food in the wet, marshy areas it inhabited. Paleontologists note that Q. northropi likely lived a solitary life, favoring habitats containing rivers and streams. Researchers have compared its feeding behavior to modern birds such as egrets and herons, which wade into water to stalk smaller prey. According to scientists, Q. lawsoni was likely a social pterosaur, and it likely sought small invertebrate prey in lakes.

　　Flight Scientists have long debated how or even whether Q. northropi could fly, given the pterosaur’s massive size and weight. Like many other flying animals, Quetzalcoatlus had hollow bones that reduced its weight, but Q. northropi was still much larger than the largest known flying birds, having a wingspan of up to 6 meters. An analysis of existing Quetzalcoatlus fossils in 2021 provided evidence that Q. northropi could indeed fly. Because of its massive wings, it likely took off by leaping some 2.5 meters (about 8 feet) into the air. With enough of a jump, it could flap its powerful wings to reach an altitude at which it could soar like a condor. Estimates suggest that Q. northropi might have flown at speeds of up to 130 km (80 miles) per hour, and covered as much as 640 km (400 miles) in a day. Researchers also discovered that, although the pterosaur’s massive wings touched the ground when the animal was walking, it probably could not use the wings to push itself forward to assist its movement on the ground.