The ability to fly is a trait shared by many different types of animals, from insects to birds and bats, says Will Newton.
The way these animals fly is very different, but they’re all capable of using muscular power to generate lift, maintain level flight, and stay airborne.
This is known as powered flight and it’s what separates true flyers from gliders, such as the confusingly named flying squirrel, flying lizard, and flying fish - none of which are actually capable of flying.
What were the first animals to start flying?
The first flying animals were insects - the only group of invertebrates known to have evolved wings and, subsequently, the ability to fly. As a group, insects started flying during the Carboniferous Period, approximately 350 million years ago and roughly 130 million years after their ancestors first appeared in the Ordovician Period.
The oldest known winged insect is Delitzschala, an extinct palaeodictyopteran that had a wingspan that measured 2.5cm across, which is roughly the same as a housefly’s. Delitzschalawas quite small by palaeodictyopteran standards, the largest of which - Mazothairos - had a 55cm-wide wingspan. It lived around 335 million years ago and probably a few million years after the first winged insects (which are yet to be discovered) took to the skies.
There’s a controversial bug known as Rhyniognatha that’s significantly older than Delitzschala, but it’s uncertain if it had wings, or if it was even an insect. A recent study has suggested that Rhyniognatha may better represent an early myriapod - a family of arthropods that includes millipedes, centipedes, and the extinct giant Arthropleura.
It’s unclear why insects developed wings - largely due to a scarcity of suitably preserved fossils from this important period - but it’s clear that once they did so they thrived, quickly becoming the largest group of arthropods in terms of species diversity. While not all types of insects can fly, most do so at some point in their life cycles.
How many times has the ability to fly evolved?
The ability to fly (i.e. powered flight) has evolved at least four times: first in insects, then in pterosaurs, then in birds, and then, finally, in bats.
There’s also a suggestion that flight may have evolved in several groups of theropod dinosaurs, independent of those that gave rise to the birds. This includes small dinosaurs like Microraptorand Changyuraptor that were unique in that all four of their limbs were fully feathered, giving them four ‘wings’ that may have been used for flying. However, the extent to which these dinosaurs could fly and stay airborne under their own power is heavily debated.
What was the first vertebrates to fly?
The pterosaurs are a particularly interesting group as they’re the only flying lineage not alive today - they faced extinction at the end of the Cretaceous Period (around 66 million years ago) alongside the non-avian dinosaurs. They’re also the first of three groups of flying vertebrates (the other two being birds and bats), emerging in the Late Triassic roughly 228 million years ago.
Like bats, pterosaurs generated lift using webs of skin (known as patagium) that stretched from the tips of their fingers to their ankles. However, unlike bats that have four elongated fingers, pterosaurs only had one elongated finger (the fourth finger); the other three were a lot shorter and were used for tasks like grasping and climbing.
The largest flying animal ever discovered was a species of pterosaur, known as Quetzalcoatlus northropi. It weighed more than 200kg and had a wingspan that measured 11m across, which is roughly the same size as a Cessna 172 aeroplane! Not all pterosaurs were giants though, some - such as the unbelievably cute anurognathids - were smaller than pigeons.
When did birds evolve?
The pterosaurs weren’t the only group of flying vertebrates to take to the skies during the time of the dinosaurs, so did the birds. The first birds lived during the Late Jurassic (around 150 million years ago) and include the famous Archaeopteryx. This raven-sized, bird-like dinosaur had features we associate with today’s birds, such as feathered wings, as well as features we consider more dinosaurian, such as a long tail and sharp, needle-like teeth.
There’s a lot of debate surrounding the affinity of Archaeopteryx and other early birds, but by the Late Cretaceous (about 72 million years ago), birds (or Aves) had established themselves and were using feathered wings, paired with their powerful pectoral muscles, to fly and dominate many different types of environments.
When did bats evolve?
The bats were the last group of flying animals to evolve, and they did so shortly after the extinction of the pterosaurs and the non-avian dinosaurs, perhaps as early as 64 million years ago based on a combination of molecular and paleontological evidence.
The origin of this mammalian group is somewhat of a mystery, as fossils of the most primitive species are incredibly scarce.
The earliest known bat is Onychonycteris finneyi. It lived 52.5 million years ago, but it had fully developed wings much like today’s bats, which suggests the ability to fly originated in the group a lot earlier.
What are the benefits of flight?
As naturally bestowed abilities go, flight is up there with one of the best. This is evidenced by the fact that all three extant groups of flying animals - insects, birds, and bats - are some of, if not the most diverse groups of animals on Earth.
The bats, for example, make up roughly 20% of all mammalian species and are only beaten by rodents when it comes to diversity amongst groups of mammals. The birds, on the other hand, boast the most species of any group of terrestrial vertebrates, with more than 11,000 recognised species. And the insects blow both of those groups out of the water, comprising more species than all other groups of animals combined.
There are many different benefits that come from being able to fly, not least the ability to - quite literally - see Earth from a bird’s eye view. In terms of evolutionary advantages, flight enables animals to evade land-based predators, access a variety of different foods, undergo long and extensive migrations, and occupy highly specialised yet incredibly productive niches, to name just a few.
However, the ability to fly isn’t necessarily the pinnacle of evolution. A lot of birds have secondarily evolved flightlessness, meaning they evolved from a flighted ancestor that, over time, lost the ability to fly for some evolutionarily advantageous reason.
There are more than 60 living species of flightless birds, from the diminutive kiwi to the giant ostrich. There are other types of flightless birds from prehistory too, some that we’ll be glad are long-extinct, such as the phorusrhacids, or terror birds.
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What are some of the weirdest ways animals take to the skies?
The most popular way to take to the skies is with a pair of wings; at least, that’s how insects, birds, and bats all do it. This isn’t the only way animals get themselves airborne, though - many different groups of animals glide, using wing-like limbs to soar through the air and surf on the wind.
The strangest gliding animal is, without a doubt, the flying fish. There are more than 64 species of flying fish, and they all ‘fly’ in a very similar way, leaping out of the water and using their specially adapted pectoral fins to glide for hundreds of metres.
It’s thought flying fish evolved this ability to avoid speedy underwater predators, such as swordfish, mackerel, tuna, and marlin. However, a downside of leaving the water is that they quickly become easy pickings for seafaring birds, such as frigate birds - one of the weirdest birds in the world.
Another strange way of getting airborne is seen in money spiders, which use silk draglines to catch the wind and propel themselves through the air. This is a method of ‘flight’ known as ballooning and it’s actually practiced by many different types of spiders, especially while they’re young. It’s not the most effective way to get from A to B though and means that any spider that tries it is at the complete mercy of the wind.
There aren’t any animals, however, that employ quite as many bizarre methods for getting airborne as we do, which range from climbing inside winged steel tubes, to strapping ourselves to contraptions made of wood and cloth - think Leonardo da Vinci’s famous flying machines - and donning specialised nylon suits that make us look like flying squirrels. There’s perhaps a reason so many of us are scared of flying…