What makes ancient, extinct animals so compelling is that they are often beyond anything we can imagine. Many of them have no comparison among the lifeforms surviving on earth today. They reached unsurpassed sizes, or were chimeric half-and-halfs. Others had alien skeletons with bodily projections and elongations that stretch credulity. There are few creatures that embody the strangeness of the extinct quite like azhdarchids.

Pronounced az-dar-kid, these giant reptiles were named after the azhdar of Iranian mythology: huge lizards with wings that populated Persian epics. Real life azhdarchids were actually pterosaurs, the group of flying reptiles most commonly recognised in the form of the head-crested Pteranodon; much beloved of scientifically dubious film and television.

Ray Harryhausen’s storyboard illustration for One Million Years BC, featuring Pteranodon. Illustration: THE RONALD GRANT ARCHIVE

“Pterosaurs are offshoots from the same line of evolution that gave us dinosaurs, including living birds,” Mark Witton, palaeontologist and freelance palaeoartist, explains. “They share a lot of basic anatomy with one another, but pterosaurs did some radical and unique things with it.”



While pterosaurs were not dinosaurs, this distinct group of reptiles evolved and lived alongside them. The whole group are sometimes erroneously referred to as “pterodactyls”, but this name is rightly reserved only for the elegant Pterodactylus antiquus, the first pterosaur to be discovered and named over 200 years ago from the Jurassic rocks of Germany. Pterosaurs were an incredibly successful group, thriving globally for 170 million years. They were a core component of Mesozoic ecosystems. Although they can be compared to the birds of today, anatomically they were quite different.

The anatomy of a pterosaur (1), bat (2), and bird (3). Illustration: John Romanes/Wikimedia Commons

I asked Elizabeth Martin-Silverstone, currently completing a PhD in the palaeobiology of pterosaurs at the University of Southampton, what made these ancient flappers so unique? “Bird wings are formed by a modified forelimb with a very reduced hand, while pterosaur wings are much longer and formed primarily by an elongated fourth digit. Imagine if you spread your arms, but your pinky finger was longer than the rest of your arm combined.” She held out her fingers to demonstrate. “Whereas birds have fleshy, feather-covered wings, pterosaur wings were formed by a membrane stretched between the end of that elongated finger, down to their legs - more similar to the membrane seen in bats.” She added, “also many pterosaurs had teeth, and modern birds do not.

Pterosaur wings were more like those of this flying fox (Pteropus giganteus) from Sri Lanka: they had membranes stretched between an elongated finger and their legs. Photograph: H Lansdown / Alamy/Alamy

Pterosaurs conquered the skies long before the first theropod dinosaurs had even a tickle of proto-feathers. They started out small, but like their dinosaurian cousins, some species ballooned to improbable proportions.

“A large number of pterosaurs lived around water bodies, plucking fish out of the water, but we also have frugivores [fruit eaters], filter-feeders, and crushing forms,” Martin-Silverstone told me, fleshing out the incredible ecological diversity of the pterosaur family tree. “Everything from small, forest-living insectivores, up to large ocean-soaring piscivores [fish eaters], and even terrestrial arch-predators.”

It is among the ranks of the latter “arch-predators” that we place the most monstrous azhdarchids. These creatures are Giger-esque. You wouldn’t bat an eyelid seeing them striding across the landscape of a far-flung planet in a science-fiction film, or scratched on a canvas, spewed from the fantastical mind of a troubled artist. As is so often the case in palaeontology, the reality is even greater than fiction. Azhdarchids were real animals that lived during the Cretaceous (108-66 million years ago). Recent examination of their fossils suggests some of them grew to become nightmarish giant land predators, roaming the prehistoric islands of Transylvania.

“In some respects, azhdarchids become more mysterious the more we study them,” Witton, co-author of a new paper describing giant predatory azhdarchids, laments. “We know enough to realise that there’s a bigger picture to these animals than we can currently grasp, but not enough to see what the picture really looks like.” This is an ironic statement coming from Witton, whose breath-taking artwork incorporates the latest discoveries and scientific understanding to speculate on the life-appearance of extinct animals.

The giant azhdarchid Witton and his co-author, Darren Naish, recently described, is Hatzegopteryx. It was named in 2002 for the town of Haţeg in Romania, near where it was discovered. This region is yielding an increasing amount of unique fossil material. Haţeg was once an isolated island surrounded by a warm, deep sea. Cut off from the mainland, many dinosaurs underwent a process known as island, or insular, dwarfism, which causes large animals to become smaller over many generations. In the Mediterranean, this led to the evolution of dwarf elephants on islands such as Crete and Malta during the ice age.

However, there is a flip-side of the process. As large animals become smaller, small animals tend to become larger. In more recent times this island-gigantism led to the evolution of large rodent species, such as the St. Kilda field mouse (Apodemus sylvaticus hirtensis), and flightless birds like the moa of New Zealand (Dinornis). In Cretaceous Transylvania, the evolutionary effects of living on Haţeg Island shrank long-necked sauropod dinosaurs down to the size of cows, while pterosaurs like Hatzegopteryx enlarged to become stocky, powerful giants.

It’s the stuff of blockbusters, but the reality of Romania’s giant pterosaurs is even greater than fiction. Photograph: Mark Witton/www.markwitton.com

“These azhdarchids were giraffe-sized, quadrupedal Panzer-storks,” Witton vividly described to me the animals he specialises in. “We have to look at the smaller, two to five metre wingspan azhdarchids, for clues to the life appearance of the big ones, but multiplying their well-known anatomy across to our giant remains creates some pretty awesome animals.”

Hatzegopteryx is so far known from only some bits of skull, partial limb bones, and a neck bone, but palaeontologists can often tell a lot from very little. The single huge neck vertebra is is evidence that it had a proportionally short and stocky neck, resistant to twisting. With no other giant predators known from Haţeg Island, Witton and Naish suggest that these animals were the apex predators of their ecosystem.



I'm pretty certain Hatzegopteryx would have no problem eating all but the largest people. Mark Witton

Although he paints many different groups of extinct animal - working on commissions for museums, fellow palaeontologists, or simply because they inspire him - Witton is renowned for his pterosaur palaeoart. So much so, some of his earlier works have become their own memes. The two Hatzegopteryx depicted in his reconstruction of the Haţeg fossils stand clothed in muted autumnal pycnofibres (the short, almost fur-like covering unique to pterosaurs), against a peachy evening sky. There is a menacing peacefulness in the way one of them holds a dwarf ornithopod dinosaur in its long, beak-like mouth. Their eyes are black and alien.



A giraffe and human provide scale for the pterosaurs Arambourgiania (centre) and Hatzegopteryx (right). Illustration: Mark Witton/www.markwitton.com

“They had two to three metre long heads, necks anywhere between one and a half to three metres long, ten metre wingspans, and standing shoulder heights of up to two and a half metres.” Witton reels off the numbers with practised ease, and like everyone who hears them, I whistle with astonishment. This is when I notice that in the background of Witton’s reconstruction, a third Hatzegopteryx has taken to the air. So, I ask, they could fly?

“Yes. Flight speeds that would get a speeding ticket on a UK road.”

Despite Witton’s certainty, whether these giants could take to the air or not is a subject of debate among pterosaur specialists.

“The biggest challenge is not actually flight itself, but take-off and landing,” Martin-Silverstone explained to me. Whereas modern birds take off by using their legs - leaping into the air or running - pterosaur anatomy may have led them to evolve their own unique method. It has been suggested that they used their powerful winged forearms to launch themselves into the air before flapping away, a method called ‘quadrupedal launch’. This meant they didn’t carry any extra weight in their legs, which is one of the burdens that limits the maximum body size of birds today.

“Research has suggested that modern ideas such as quadrupedal launch allow for a maximum size limit of around eleven or twelve metre wingspans. After this, the animal likely wouldn’t have been able to launch.” Martin-Silverstone said. So if pterosaurs launched quadrupedally, it could have allowed animals the size of Hatzegopteryx to retain the ability to fly. “More work needs to be done to figure out exactly what was possible and what the limits are to this idea.”

If pterosaurs were so successful, exploiting all these different environments and niches and becoming giant apex predators, what happened to them? “Pterosaurs were quite successful until at least the Early Cretaceous,” Martin-Silverstone answered. “At this point, we see the fossil record of pterosaurs start to grow a little more sparse. Unfortunately it’s not clear if this is because the number of pterosaurs decreased, or because the fossil record didn’t preserve them [because they] have extremely fragile bones. We do know that along with non-avian dinosaurs, pterosaurs went extinct at the end of the Cretaceous in the K-Pg extinction event.”

The distribution of azhdarchids in the Cretaceous. Photograph: PLoS One/Mark Witton/Ron Blakey

Mark Twain wrote, Truth is stranger than fiction, but it is because Fiction is obliged to stick to possibilities; Truth isn’t. As more of earth’s ancient past is recovered by palaeontologists, we continue to be astonished by their discoveries. Evolution has resulted in unexpected solutions to the problems of survival.

It appears that it is not just our imaginations that are populated by monsters.

References

Buffetaut, E, Grigorescu, D, Csiki, Z. 2002 A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften. 89: 180–184.



Habib, HB. 2008 Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28, 159-166.

Naish D, Witton MP. 2017 Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators. PeerJ 5:e2908



Vremir M, Kellner AWA, Naish D, Dyke GJ. 2013 A New Azhdarchid Pterosaur from the Late Cretaceous of the Transylvanian Basin, Romania: Implications for Azhdarchid Diversity and Distribution PLoS One 8.1: e54268.