---
title: "Flying and gliding animals"
chunk: 3/8
source: "https://en.wikipedia.org/wiki/Flying_and_gliding_animals"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:46:37.316378+00:00"
instance: "kb-cron"
---

Powered flight has evolved unambiguously only four times—birds, bats, pterosaurs, and insects (though see above for possible independent acquisitions within bird and bat groups). In contrast to gliding, which has evolved more frequently but typically gives rise to only a handful of species, all three extant groups of powered flyers have a huge number of species, suggesting that flight is a very successful strategy once evolved. Bats, after rodents, have the most species of any mammalian order, about 20% of all mammalian species. Birds have the most species of any class of terrestrial vertebrates. Finally, insects (most of which fly at some point in their life cycle) have more species than all other animal groups combined.
The evolution of flight is one of the most striking and demanding in animal evolution, and has attracted the attention of many prominent scientists and generated many theories. Additionally, because flying animals tend to be small and have a low mass (both of which increase the surface-area-to-mass ratio), they tend to fossilize infrequently and poorly compared to the larger, heavier-boned terrestrial species they share habitat with. Fossils of flying animals tend to be confined to exceptional fossil deposits formed under highly specific circumstances, resulting in a generally poor fossil record, and a particular lack of transitional forms. Furthermore, as fossils do not preserve behavior or muscle, it can be difficult to discriminate between a poor flyer and a good glider.
Insects were the first to evolve flight, approximately 350 million years ago. The developmental origin of the insect wing remains in dispute, as does the purpose prior to true flight. One suggestion is that wings initially evolved from tracheal gill structures and were used to catch the wind for small insects that live on the surface of the water, while another is that they evolved from paranotal lobes or leg structures and gradually progressed from parachuting, to gliding, to flight for originally arboreal insects.
Pterosaurs were the next to evolve flight, approximately 228 million years ago. These reptiles were close relatives of the dinosaurs, and reached enormous sizes, with some of the last forms being the largest flying animals ever to inhabit the Earth, having wingspans of over 9.1 m (30 ft). However, they spanned a large range of sizes, down to a 250 mm (10 in) wingspan in Nemicolopterus.
Birds have an extensive fossil record, along with many forms documenting both their evolution from small theropod dinosaurs and the numerous bird-like forms of theropod which did not survive the mass extinction at the end of the Cretaceous. Indeed, Archaeopteryx is arguably the most famous transitional fossil in the world, both due to its mix of reptilian and avian anatomy and the luck of being discovered only two years after Darwin's publication of On the Origin of Species. However, the ecology of this transition is considerably more contentious, with various scientists supporting either a "trees down" origin (in which an arboreal ancestor evolved gliding, then flight) or a "ground up" origin (in which a fast-running terrestrial ancestor used wings for a speed boost and to help catch prey). It may also have been a non-linear process, as several non-avian dinosaurs seem to have independently acquired powered flight.
Bats are the most recent to evolve (about 60 million years ago), most likely from a fluttering ancestor, though their poor fossil record has hindered more detailed study.
Only a few animals are known to have specialised in soaring: the larger of the extinct pterosaurs, and some large birds. Powered flight is very energetically expensive for large animals, but for soaring their size is an advantage, as it allows them a low wing loading, that is a large wing area relative to their weight, which maximizes lift. 

== Biomechanics ==

=== Gliding and parachuting ===
During a free-fall with no aerodynamic forces, the object accelerates due to gravity, resulting in increasing velocity as the object descends. During parachuting, animals use the aerodynamic forces on their body to counteract the force of gravity. Any object moving through air experiences a drag force that is proportional to surface area and velocity squared; this force will partially counter the force of gravity, slowing the animal's descent to a safer speed. If this drag is oriented at an angle to the vertical, the animal's trajectory will gradually become more horizontal, and it will cover horizontal as well as vertical distance. Smaller adjustments can allow turning or other maneuvers. This can allow a parachuting animal to move from a high location on one tree to a lower location on another tree nearby. Specifically in gliding mammals, there are 3 types of gliding paths respectively: S glide, J glide, and "straight-shaped" glides where species either gain altitude post-launch then descend, rapidly decrease height before gliding, or maintain a constant angled descent.
During gliding, lift plays an increased role. Like drag, lift is proportional to velocity squared. Gliding animals will typically leap or drop from high locations such as trees, just as in parachuting, and as gravitational acceleration increases their speed, the aerodynamic forces also increase. Because the animal can utilize lift and drag to generate greater aerodynamic force, it can glide at a shallower angle than parachuting animals, allowing it to cover greater horizontal distance in the same loss of altitude, and reach trees further away. Successful flights for gliding animals are achieved through 5 steps: preparation, launch, glide, braking, and landing. Gliding species are better able to control themselves mid-air, with the tail acting as a rudder, making it capable to pull off banking movements or U-turns during flight. During landing, arboreal mammals will extend their fore and hind limbs in front of itself to brace for landing and to trap air in order to maximize air resistance and lower impact speed.

=== Powered flight ===