Pterosaurs are very recognisable prehistoric reptiles, but they’re often overshadowed by dinosaurs’ immense popularity.
© Noiel/ Shutterstock
Pterosaurs: The truth about these ‘flying dinosaurs’
Emily Osterloff
During the Mesozoic Era, while dinosaurs ruled the land and giant marine reptiles dominated the oceans, the skies were filled with another kind of reptile – the pterosaurs.
Pterosaurs – or pterodactyls as you may also have heard people refer to them – are one of Hollywood’s great scene-setters. In the same way that a tumbleweed rolling on by evokes a Western, chuck a pterosaur in the sky and you’re whisked into a prehistoric world.
But forget what you think you know about pterosaurs being flying dinosaurs. If you take a closer look, you’ll find that they’re actually their own brand of winged reptile and a fantastic tale of mysterious origins to breathtaking diversity.
What is a pterosaur?
This is a cast of a Dsungaripterus skull. This pterosaur had upturned, pincer-like jaws, as well as chunky teeth further back in the mouth that may have helped it crush hard-shelled organisms. It would have had a soft tissue crest in life, supported by the bony protrusion across the top of its skull.
Today, birds fill our skies with a stunning array of shapes, colours and sizes. But back in the Mesozoic Era, a group of reptiles called pterosaurs were the dominant force in the air. In fact, pterosaurs were the first vertebrates to evolve powered flight.
They predate birds by a considerable margin. The first pterosaurs turn up in the fossil record around 215 million years ago, in the Late Triassic. The earliest dinosaurs to be described as bird-like, creatures such as Anchiornis and Archaeopteryx, appeared much later from 165 to 150 million years ago in the Late Jurassic.
More than 200 species of pterosaur have been discovered, and palaeontologists are regularly finding more.
They had a variety of lifestyles. Some pterosaurs led lives similar to today’s seabirds, feasting on fish. The toothy jaws of Anhanguera, for example, appear well adapted for gripping onto such slippery prey. But fish-eating pterosaurs didn’t all have teeth. Specimens of the toothless pterosaur Pteranodon have been found with fossilised stomach contents that include fish remains. It’s quite possible that these pterosaurs were snatching fish out of the water, like some of our equally toothless, modern seabirds do.
Other pterosaurs had jaws for tearing flesh, and there were some with sharp beaks for hunting land-based vertebrates that possibly stalked their prey in a similar way to herons. There were even pterosaurs with long, comb-like teeth. Combined with a weak bite force, these reptiles may have been filter feeders, a bit like modern-day spoonbills, hunting for very small animals, such as krill-like shrimps.
Pterosaurs started out as relatively small animals. But eventually they evolved into forms that Dr Mike Day, our pterosaur curator, describes as “enormous and bizarre”. On a visit to the palaeontology collections, he proves this point by plucking a large, knobbly object from a shelf. What this bowl-shaped item, approximately 23 centimetres wide, turns out to be is a cast of a small section of arm bone belonging to Quetzalcoatlus.
Living roughly 68 to 66 million years ago, Quetzalcoatlus belonged to a group of pterosaurs known as azhdarchids. They’re the largest animals to ever evolve to fly, with wingspans of around 11 metres – the same as a small aeroplane. On the ground, the enormous Quetzalcoatlus stood at around 2.5 metres tall at the shoulder – an adult giraffe is only slightly taller at the shoulder at 2.75 metres. With long necks and large heads added too, they were practically the same height.
This is the “cookie-cutter” grin of Istiodactylus. Discovered on the Isle of Wight, this pterosaur may have been a vulture-like scavenger, using its sharp teeth to tear into food.
This is Balaenognathus, a name that means ‘bowhead whale jaw’, alluding to its baleen-like teeth, which would have been used for filter feeding. Look closely at this fossil from the Naturkunde-Museum Bamberg and you’ll spot jaws full of long, thin teeth all squashed closely together.
© DM Martill, E Frey, H Tischlinger, M Mäuser, HE Rivera-Sylva & SU Vidovic (CC BY 4.0) via Wikimedia Commons
How did pterosaurs fly?
The bit of Quetzalcoatlus Mike held up was the end of a humerus. In mammals like us, the humerus is the longest part of our arms, but in pterosaurs, it’s one of the shorter arm bones.
In comparison, pterosaurs’ little fingers could be longer than the rest of their lower arm bones. This extraordinarily long digit played a very important role – supporting their wings.
Pterosaur wings were thin membranes of skin, reaching from the arms to the ankles.
Modern-day bats have wings made from leathery skin that’s stretched between the bones of their hand. Their long, spread-out fingers help to support and control the wing in flight. Whereas in most pterosaur species the little finger held up the wing and the rest of their fingers made up a useable hand. Instead of bones, pterosaurs had fibres running down and across the wing, giving it structure.
But how could a giraffe-sized animal fly? To answer that, we need to look inside their bones.
Like those of birds, the bones of pterosaurs are mostly hollow and filled with air, making what might otherwise be a hefty animal surprisingly light for its size. Quetzalcoatlus, for example, is estimated to have weighed up to 250 kilogrammes – incredibly light compared to giraffes, which can weigh more than 1,000 kilogrammes.
It’s also hard to miss the gaping holes in the sides of some pterosaur skulls. These holes, Mike explains, comprise a very enlarged nostril and a second opening called an anteorbital fenestra. This would have reduced the overall weight of their large heads. We see fenestration in the skulls of dinosaurs too, but it’s more extreme in pterosaurs.
Dimorphodon macronyx is a Jurassic pterosaur from Lyme Regis, on the UK’s south coast. The minimal bone in this pterosaur’s skull would have kept its large head quite light in life. This is one of two incredible Dimorphodon specimens in the pterosaur collections we care for that were acquired by Sir Richard Owen in the nineteenth century.
We think pterosaurs could walk about on the ground on all four limbs, as we’ve found their fossilised footprints. To get airborne, some scientists think that they would have launched into the air with one great leap, with larger species potentially needing a bit of a run up. However, not everyone agrees with this theory.
Once in the air, a pterosaur’s size may have affected how it flew. Larger species may have been like albatrosses, using air currents to generate lift. This would have let them soar over long distances, only occasionally flapping their giant wings.
Smaller pterosaurs may have been more like smaller birds. With shorter wings, they would likely have been much more agile in the air. There are some pterosaurs that, besides their wing fingers, had really reduced hands and feet, indicating that they may have spent most of their time in the air.
Anhanguera had large eye sockets, suggesting it may have had very large eyes and good vision. CT scanning skulls like this has also revealed that pterosaurs may have had brains that were in some ways similar to birds’.
Are pterosaurs flying dinosaurs?
Dinosaurs’ immense popularity seems to muddy the water when it comes to popular thinking about prehistoric reptiles. Pterosaurs are one of the victims of this, often incorrectly being marketed as ‘flying dinosaurs’.
Pterosaurs and dinosaurs are both members of a group called the archosaurs, which means they’re related to one another. But dinosaurs didn’t evolve into pterosaurs, and pterosaurs didn’t evolve into dinosaurs. Instead, somewhere further back in time, the lines leading to these two groups split. At the point where this happened, there would have been an animal that wasn’t a dinosaur or a pterosaur but was an ancestor to both. Both pterosaurs and dinosaurs appeared in the Late Triassic, so this common ancestor occurred at some point before this.
Birds evolved from dinosaurs, which means that despite some of their apparent similarities, pterosaurs also aren’t birds or ancestors of them. These two groups are an example of convergent evolution – where unrelated animals adopt similar characteristics, often as solutions to similar problems. The difference between pterosaurs, flying dinosaurs and birds can, at its simplest, be boiled down to the structure of their wings and how their wings function.
Pteranodon was the first pterosaur found in the USA. You’ll find this cast on display just inside our East entrance. It’s a great demonstration of how pterosaurs’ elongated little fingers were a fundamental part of their wings’ structure.
Why did pterosaurs go extinct?
Pterosaurs were around until the end of the Cretaceous Period, 66 million years ago. Their extinction coincides with when an asteroid collided with Earth. This event also wiped out the dinosaurs and a host of other animals in one of the planet’s five great mass extinctions.
Up until then pterosaurs were thriving. In the latter part of the Cretaceous, several pterosaur groups were still around, including giants such as Quetzalcoatlus.
But if pterosaurs were so bird-like, why did they die out but birds survive? Well, it may come down to size. Generally speaking, larger animals were more susceptible to extinction. The smallest pterosaurs at the end of the Cretaceous were about the size of the biggest birds.
Birds’ small sizes at the end of the Cretaceous suggests they weren’t competing with the largest pterosaurs, and so birds probably didn’t drive pterosaurs extinct. But with the gap left behind by pterosaurs and archaic birds going extinct, the surviving birds had a wide-open opportunity to diversify and grow to larger sizes with very few competitors around.
Early pterosaur discoveries
Mary Anning is famous for her marine reptile discoveries, but in 1828 she uncovered something quite different – a pterosaur. We now know this animal as Dimorphodon. You can find this specimen on display on the first-floor balconies of our Hintze Hall.
Western scientists started finding pterosaur bones some 40 years before the first-named dinosaur, Megalosaurus, was discovered.
The first pterosaurs were uncovered in the Solnhofen limestone in Bavaria, Germany. In the Late Jurassic, the extremely fine sediments that settled in what was then a quiet lagoon environment have preserved some exquisite fossils.
Discovered there in 1784, the first known pterosaur was eventually dubbed Ptéro-dactyle – meaning ‘wing finger’ – and is likely why so many of us today know pterosaurs as pterodactyls. This was later converted into the Latin name we now use for this animal, Pterodactylus.
All pterosaurs discoveries were made in Germany until the 1820s when fossil hunter Mary Anning uncovered a pterosaur at Lyme Regis on the UK’s south coast. Palaeontologist William Buckland initially called it Pterodactylus macronyx, but it was later renamed as Dimorphodon by Sir Richard Owen, our first Superintendent.
Dimorphodon is a curious creature. It’s quite an early pterosaur species, Mike says, pulling out two prize specimens purchased and added to the collections we care for by Richard Owen long ago.
Like many other pterosaurs, they’ve got noticeably large, sharp teeth. These run all along the top jaw but are only right at the front of the lower jaw.
“If you look closely, on the back part of the lower jaw, it’s got lots of tiny teeth, hence Dimorphodon, which means ‘two kinds of teeth’. These are very different from the corresponding teeth in the upper jaw, which is unusual for animals, generally,” Mike explains.
Get up close and you’ll see loads of tiny, little teeth running along Dimorphodon’s lower jaw. Micro-wear patterns on Dimorphodon teeth suggest these pterosaurs ate small vertebrates.
Apart from a few incredible fossils like these, most of the pterosaurs we find here in the UK are just fragments. We mostly find isolated wing bones. This is because pterosaur bones are quite fragile, as they’re air-filled to enable flight. To fossilise well, perfect conditions, such as calm, oxygen-free (anoxic) lakes or marine environments were needed. Even if conditions were right, there was still a chance that scavengers or waves could disrupt the remains, slimming the chances of them becoming a fossil.
What this ultimately means for us today is that there are lots of gaps in the pterosaur fossil record.
Flying reptile renaissance
With an initial steady flow of specimens from 1784 onwards, efforts to understand these bizarre new animals took off. But by the mid-twentieth century, research had stalled.
It’s only been in the last few decades, with the benefits modern technology brings, that pterosaur science has flourished again.
Mike points out one of the collection’s Solnhofen specimens – a pterosaur called Rhamphorhynchus. Its skull noticeably sticks out from the slab of sandy-yellow rock it’s embedded in. According to Mike, for it to be this uncompressed is quite unusual.
As one of the largest Rhamphorhynchus ever found, it’s an impressive specimen to see in person. But sometimes, what you can’t see in fossils makes pterosaurs even more interesting.
Using ultraviolet light and laser-stimulated fluorescence (LSF), which light up certain minerals, scientists are revealing tail vanes and fibres within the wing membranes that are invisible to the naked eye. Research using these techniques very recently revealed these structures in two other Rhamphorhynchus specimens in the collections we care for.
This Jurassic pterosaur is called Rhamphorhynchus muensteri. This fossil is the largest example of this species found so far, with an impressive wingspan of 1.8 metres.
We also know that pterosaurs with crests were quite widespread.
“Some pterosaurs had a short, bony crest on the top of their head. We now know that this often acted as a foundation for a larger crest made of soft tissue, which was bigger and more elaborate,” explains Mike. Pigment cells have been reported, and it’s believed these crests may have featured colours, which may have been used for signalling. However, scientists are uncertain if these colours can be reliably interpreted.
The pterosaur collection we look after might be relatively small, with only around 1,000 specimens and casts, but it’s still yielding fascinating discoveries.
“Despite the collection being modest, it’s heavily used because of its historic significance, and we’re getting more and more out of these old specimens as technology advances,” says Mike.
Mysterious origins
Pterosaurs first appear in the fossil record with a bit of a bang.
With other ancient animals, palaeontologists can sometimes use fossils to track the slow evolution of a group over time. But for pterosaurs, even the earliest examples already have a distinctly pterosaur-like set of characteristics.
It was only in 2020 that scientists worked out what pterosaurs were most closely related to – a group of small reptiles called lagerpetids. Another reptile called Scleromochlus, which lived up to 235 million years ago in what’s now Scotland, also seems closely related to both. It’s the final flourish of Mike’s pterosaur tour.
The rocks he carefully pulls out this time would fit neatly in your hands. The 18-centimetre-long Scleromochlus specimen within shows us what the common ancestor of pterosaurs and lagerpetids might have looked liked. That we’d go from a small animal like this to giraffe-sized pterosaurs is an incredible feat of evolution.
Scleromochlus isn’t an ancestor of pterosaurs but is one of the most closely related animals we’ve found so far. The impressions in this rock were left by bones that decomposed long ago.
But there’s a catch. To the untrained eye, this Scleromochlus specimen is just a jumble of scars across the rock where bones have long since disintegrated. It’s taken CT scanning to put this prehistoric puzzle back together and what it’s revealed is that this animal was not actually particularly pterosaur-like.
“When you see the reconstruction, it still looks ostensibly like a small, bipedal reptile, much more like what you’d imagine a tiny, slender, bipedal dinosaur to look like,” Mike points out.
Somewhere between Scleromochlus and the earliest pterosaurs we’ve found, something happened that drove the pterosaur line to evolve for a life in the skies. But until we uncover fossils that show how and when that transition happened, pterosaurs have left us with quite the cliffhanger.
Let’s hope they don’t leave us waiting too long to find out the answer.
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