A diagram of the wing shape of flying vertebrates, including birds (black), pterosaurs (blue), and a bat (red). Based on JMV Rayner (1988), "Form and Function in Avian Flight", fig. 14D & 16D (link) and MP Witton (2008), "A new approach to determining pterosaur body mass and its implications for pterosaur flight", table 4 (link).
The two axes represent wing loading (body weight divided by wing surface) and aspect (length-to-width ratio), independent from overall size. While the distribution of species is mostly continuous, there are "regions" corresponding to particular wing shapes and flight styles.
Starting in the lower-right region of high loading and low aspect (small, short wings and heavy bodies) we find saltuary flyers like gamefowl (e.g. pheasants, turkeys) and, presumably, the pterosaur Dimorphodon. These species only fly in short bursts to escape ground-based predators. This is not a primitive trait: both gamefowls and Dimorphodon have ancestors that were better flyers.
If we keep wing loading high and increase wing aspect, we move upward into the divers: birds like ducks, grebes, puffins, and auks that dive into water to feed and so have relatively heavy bodies. Narrow wings help them acquire speed as they plunge into water.
The highest wing aspect is found among marine soarers, of hich the purest example is the albatross (and the pterosaur Nyctosaurus, who has the highest wing aspect ever recorded). At the edges of this cluster, gulls transition between marine soarers and aerial predators, and gannets between marine soarers and divers.
Aerial predators, who hunt in mid-flight, have low loading and mid-to-high aspect to be as fast as possible. Insectivores like swifts and swallows have narrow, swept-back wings, whereas bird-eaters like harriers and falcons have broader wings. Here we also find the tiny insectivorous pterosaur Anurognathus.
Beneath, with the lowest wing aspect, we find thermal soarers, who fly long distances over land exploiting rising thermal currents. They tend to have broad wings with slotted ends, like storks and vultures. Here we also find the largest bats and giant azhdarchid pterosaurs such as Quetzalcoatlus.
Finally, near the center we find versatile, unspecialized terrestrial flyers like parrots and pigeons. Hummingbirds, with a unique hovering flight, appear near the divers, though for rather different reasons.
