We’ve known them as ancient, mythical, winged, pyromaniacal reptilian beasts with a flair for the dramatic and destructive. They have been a fixture in our lore, in some form or another, the world over. While most of these tales of dragons are fictional, or at least highly embellished, there is still a very strong chord of truth in them. The blaze-setting, screeching hell-drakes so common in storybooks have not existed for a very long time, and it is unlikely that Medieval humans actually had contact with them (this stands in contrast with unicorns, which went extinct in 1982 when the last specimen escaped from her enclosure and ingested some antifreeze). However, dragons have had a rich and colorful evolutionary history that dates back 225 million years, and their unique biology and rise and fall in biodiversity is worth discussing.

The earliest known ancestor for the dragon lineage (otherwise known as the order Daemovespera, or ‘demon bats’), is the basal archosaur Postosuchus.

That is quite the disconcerting smile there, friend.

This animal may have looked like a skinny-legged T-rex with horrible posture, but it predates tyrannosaurs by quite a long ways in geologic time. It was a rauisuchian, a member of a group of reptiles that lived approximately 200 to 250 million years ago which eventually gave rise to modern crocodiles and alligators via a splintering sister group. However, back in the Triassic, rauisuchians were much more diverse, and had many apex predators among their ranks. While most of them were out-competed by their dinosaurian cousins by the Jurassic period, some (like the ancestors of crocodilians) and the proto-dragons, flourished.

Postosuchus was a wickedly powerful macropredator of the tropical Triassic forests of Texas. It was as long as a Ford Expedition, and probably weighed as much as a grizzly bear. Also, it had a skull that looked like this:

The dentition shows clearly that it had a diet primarily consisting of babies.

Ol’ Posty also had the distinction of being one of the largest and meanest bastards in its ecosystem, and could quite easily take down just about anything it wanted. At this point in time, most early dinosaurs were scrawny, turkey-sized pipsqueaks, and likely served as food for their knife-mouthed cousin. Postosuchus ruled with a scaly fist, and I mean that quite literally, because this creature was probably among the first archosaurs to experiment with bipedalism, and actually had fists.

Postosuchus had front limbs that were much smaller and shorter than its back limbs, which would indicate that it at least had ability to rear up and bring its terrifying face even higher off the ground. However, its hind limbs didn’t have nearly the type of strength or musculature seen in truly bipedal archosaurs, like dinosaurs, suggesting that if it could walk on its hind legs, it couldn’t do it for very long. There is some disagreement among paleontologists on how much this animal could take moving around on its haunches, but it seems likely that it engaged in both types of locomotion, alternating between galloping around on all fours with its ass high in the air, nose in the dirt, eyes menacingly focused on its prey…and as an ungainly, pillar-erect dino-gator, storming through the brush, making every animal in the forest defecate itself in fear.

This experimentation with bipedalism is important, as it was from Postosuchus that later rauisuchians, increasingly more bipedal, had their front limbs free from the role of locomotion. As the Triassic progressed into the Jurassic, and dinosaurs rose to dominance, it was the slow, lumbering, quadrapedal archosaurs that met their demise because they couldn’t cut the evolutionary mustard. However, the two-legged, T-rex-esque offshoots of the Postosuchus line were able to compete in many different biomes. Millions of years ticked by, and they spread from proto-North America, across the northern supercontinent of Laurasia, and diversified, occupying territory that would become Europe and parts of  Asia as plate tectonics shifted continents around along the surface of the Earth.

Many of these predatory creatures, now with their hands free, are thought to have used them for grasping prey much like their dinosaur relatives. Some smaller, sinewy clades, living in the tall coastal forests around the supercontinent, also began using their clawed forelimbs for climbing into trees and hunting the animals that lived there. These arboreal reptiles, some as small as cats, and others the size of bears, proliferated and dominated a lifestyle that no other reptilian had attempted yet.

By the end of the Jurassic, predatory theropod dinosaurs, the likes of Allosaurus and Saurophaganax, had become large, fast, intelligent, unstoppable killing machines. Some reached lengths of over 40 feet and weighed several tons. The big bipedal rauisuchians were limited by their inefficient, crocodile-like ankle structure, and couldn’t develop the swift athleticism or size common to the dinosaurs with which they were competing for territory and food. So, this group began dropping like flies. But, their tree-dwelling hippie cousins in the forests bordering the shorelines were expanding and diversifying, and some groups were evolving new prey-capturing tricks. The first of these new abilities was stereoscopic vision (evidenced by forward facing eye sockets), which allowed the depth perception required for scampering around in the canopy and targeting food. The other new trait that had become a successful tool in the trees was the use of fire.

Roughly 160 million years ago, one group of tree-dwelling proto-Daemovesperans inhabiting the tropical islands of what would eventually become Europe, developed the fire-breathing trait. It began when this lineage evolved a symbiotic relationship with several species of bacteria in their gut. This relationship first developed due to the selective pressures associated with eating heavily armored tree-dwelling reptiles. There were many species of thickly armored, arboreal lizards that made their residence in the pre-European island chain. The plates on the outsides of these creatures were too tough to digest for the early dragons, but since the armored animals were plentiful, any creature that could successfully eat them would have a significant evolutionary edge. So, it was a mutant offshoot of the tree-dragon line that had a close association with bacteria in a special pouch at the front of its digestive tract that received this boost. The bacteria produced sulfuric acid, which, combined with the specially adapted stomach lining of the dragon, made digestion of these armored reptiles possible. Over time, it was this subgroup that supplanted the rest of their relatives on the islands.

One by-product of this symbiotic relationship was the production of hydrogen gas as waste. For millions of years, it was likely belched out harmlessly throughout the day. However, one group that began deviating away from the exclusive diet of tough, plated reptiles began co-opting this special waste product for its own use. Many species in this particular group were very small, gracile creatures, and were often food for their larger relatives. As a means of deterring and startling predators, they evolved a reinforced sac (evidenced in the fossil record by ossified struts extending from neck vertebrae) from the bacterial pouch that connected to the esophagus via a stout valve. This organ, housing the precious bacterial culture, produced and housed large amounts of pressurized hydrogen gas, which would be rapidly expelled from the mouth in the event of a threat. This giant, deafening burp, possibly combined with brightly-colored skin flaps around the mouth, was usually enough to confuse a predator long enough for the attacked to escape.

It wasn’t long for subgroups of this ‘gas dragon’ group to start using the hydrogen organ (also known as a ‘tank’) in creative ways. The most important development came in the ingestion of inorganic platinum from cliff-side rocks which were chewed up and swallowed. We can see this in the fossil record through the presence of platinum-rich deposits in the skulls of these animals, as well as tough, wear-resistant teeth, often also capped with platinum deposits. The combination of the sulfuric acid from the tank, and the hydrochloric acid in the stomach, gave the digestive system of dragons an enhanced punch; the combination of these acids, a mild form of ‘aqua regia’, was capable of dissolving many types of metals, including gold and platinum. This metallic platinum was distilled in the gut from chewed up rocks, and incorporated into an ossified sheath surrounding cartilaginous projections off the back of the mandible. These projections, capped with a bony shell, were formerly used in communication in more social, intelligent species; screeching or roaring could accidentally expel precious hydrogen, but the clicking of the ‘clackers’ in the back of the throat could be used as vocal communication quite easily. When a platinum layer was infused on the surface of these clackers, they could be rubbed together with great force, and the friction could produce a spark. In the presence of a jet of hydrogen gas expelled from the tank, that spark, catalyzed by platinum and hydrogen’s special chemical relationship, would produce a hot flame plume, the mechanism working similarly to a flint lighter and a Bunsen burner.

This new tool was incredibly useful for defense against larger tree-dragons, as well as for sniping and roasting animals from across the tree branches (which also incidentally caused wide-spread forest fires; it is thought that the evolution of fire-breathing dragons served as one of the first selective pressures for fire-adapted vegetation). As fire-breathing dragons rose in dominance, and other tree dragons went extinct, the islands of Europe began coalescing, and these animals started diversifying as their environments changed from coastal forest, to variable landscapes of mountains and deserts. Many of the species that congregated around exposed cliffs to ingest platinum began to fit into an even more intense climbing lifestyle, and never left the sides of the cliffs. Some are thought to have even evolved large bits of webbed skin that stretched between their front limbs and their flanks. This would have allowed them to effortlessly glide on the wind between cliffs. Over millions of years, in some lineages, this transitioned into full-sized wings developed from the front limbs. By the start of the Cretaceous, the face of the dragon was one with powered flight and the ability to scorch the earth at will.

For the next 80 million years, dragons proliferated as they filled the skies and left their forming European subcontinent, spreading to almost every corner of the globe. They grew in size, and their tank organs became even more specialized and hardy, increasing in size to fill the entire gullet of these animals. Because of this expansion of the hydrogen tank, dragons became especially vulnerable to lightning strike; a bolt of lightning to hit a dragon would invariably kill it, as the hydrogen tank would ignite and the beast would explode in a fiery ball of intestines and bone. Dragons openly competed with many of the now highly-specialized dinosaur groups, and some were even large enough to hunt and kill various dinosaurian species. They became the largest animals of the skies, and over tens of millions of years, dramatically reduced the diversity of the pterosaurs sharing the skies with them.

Included below is a phylogenetic tree showing some of the relationships of the groups of dragons to arise in this period of time:

A larger version can be found here: Bingo

About 65 million years ago, when dragons were at the height of their diversity, they suffered the tragedy of getting slammed in the face with a giant asteroid. Most species, along with all the large animals on Earth, including dinosaurs, went extinct in the fiery, ashy  aftermath. However, some smaller, more generalized species made it through the extinction event, and wheeled around in the skies for many millions of years after that, just as mammals were beginning their own Age. Dragon diversity never recovered from the event at the end of Cretaceous, and as the climate began to dry and cool around 20 million years ago or so, various once-terrifying families of dragons began to fade away. Oxygen levels in the atmosphere fell from Mesozoic levels, and the oxygen-hungry, high-metabolism flying dragons no longer became physical feasible. By the time first Ice Ages rolled around, the few remaining lineages of dragons were greatly reduced in size, flightless, and scattered around the planet in isolated locations where they survived as ‘living fossils’. Repeated glaciations during the Ice Ages did many of these species in, but even today, two relict, distantly-related dragons still exist.

The first of these is the famous Komodo dragon (Varanus komodoensis) of Komodo Island in Indonesia. They are known as the largest lizards on the planet, but in reality, their namesake is a far more accurate declaration of their phylogenetic relationships with other reptiles, as they are relatively diminutive, flightless members of the Pyrospira suborder of dragons. These animals are the size of crocodiles, but far more nimble on land, and thus, much more capable of dragging a small child off into the scrub before you can say ‘fast food.’ While Komodo dragons no longer have the ability to produce flame, and have lost completely their clackers in their throats, they are the top predators in their island ecosystem, routinely taking down adult oxen and anything else stupid enough to share the dirt with these sickle-clawed nightmares.

It was not very long ago that one the Komodo dragon’s close relatives, one that miraculously still possessed the fire-breathing trait, existed in nearby Australia. This relative, Megalania (Varanus prisca), formerly known as Megalania prisca, lived up until about 40,000 years ago in the grasslands of Australia. Hoardes of dragonslayers crossed the land bridge from Southeast Asia into the continent and killed every last one of them over the course of as little as two or three thousand years.

“I’m not trying to eat you! Run! The humans will get you too!”

Megalania was much larger than its Komodo dragon relative. Long enough to have difficulty fitting in your living room, and tall enough to look you squarely in your gooshy, defenseless belly full of viscera, Megalania had a broad skull as long as your arm, equipped with iron strong jaws and sharply hooked fangs. Megalania weighed as much as your Camry, but had better acceleration over open ground. Megalania dominated the Australian outback for millenia, tossing giant marsupials the size of rhinoceroses around like rag dolls and generally just being a belligerent dick.

Most people are not aware of the fact that Megalania was a being that could eject flames from its blade-toothed face…because apparently it just wasn’t horrible enough. It would cook emus and other giant flightless birds like outsized rotisserie chickens on the hot plains, charring the landscape as it did so. In fact, Megalania’s flamethrower habits were enough to cause regular, widespread wild fires all over the Australian countryside. Eucalyptus woodlands were, at any time, susceptible to being torched by any given uncaring, Smokey the Bear-enraging Megalania in search of a quick meal. Sometimes, just because they were cruel, Megalanias would team up and intentionally burn down entire forests, just so they could catch any animals inside that were too slow to get out of the way, and dine on their medium-well remains as they passed through.

No rules. Just right.

Humans haven’t slain the remaining populations of Komodo dragons yet, but if they did, I wouldn’t deny that being a wise decision. Instead of deadly flames, Komodo dragons are in possession of something equally as deadly, but just more intimate and gross.
The saliva of Komodo dragons is laced with a toxic cocktail of venom extruded from glands in the jaw, as well as massive colonies of bacteria picked up from whatever dead animal the dragon happened to tear apart that week.

Good god. Stop it. It’s only cute when a dog slobbers like that.

A single, wet bite from a Komodo dragon can put down any large mammal in a matter of a day (including humans), due to the debilitating effects of the venom on the neural and muscular systems. In fact, this is the highly efficient means by which this little dragon hunts large, powerful prey. Bite once or twice, let the animal break free, and then wait for it to tire and succumb to infection (from a massive, gushing wound exposed in a tropical environment full of microbes) and weakness, following it through the tropical forest with a keen sense of chemoreception on a long, forked tongue. Biological excellence, my friends.

The other surviving dragon is also found in the region; in the deserts of Australia. It is the bearded dragon (Pogona), and while it is very small (only weighing up to a pound or two), it packs a rarely observed wallop. Bearded dragons are popular in the exotic pet trade, and make beautiful and easy to care for reptilian companions. Their ‘bearded’ description comes from the spiny scales around their throat, which upon expansion of the skin in a threat display, resembles a thick, manly, imposing ring of epic facial hair…which, like real hair beards, is enough to stop enemies in their tracks.

“You….shall not….pass!”

Bearded dragons are popular as pets for children because of their easy temperament, but underneath that adorable, friendly exterior lies the heart of a mythical killer, conserved in the genetic code for hundreds of millions of years. The old behaviors of munching on rocks for platinum are long gone in bearded dragons, but if given platinum-laced food, their almost vestigial clackers will begin to accumulate a platinum coat. Within a few weeks, they may begin to produce short, accidental ignitions. Bearded dragons are omnivores, and can’t hunt anything bigger than a fat grasshopper anyways, so their superheated belches are never used aggressively, but are simply a quirky carryover from their illustrious genetic past. Platinum-fed bearded dragons are usually, wisely, kept in special fireproof cages as to reduce the risk of fire hazard, and are typically kept out of the hands of anyone not wearing protective clothing. Uses for these pets are few and far between, due to the fact that the flames ejected from these little guys usually produce more detrimental risk or injury or liability than benefit. Some exploit their platinum-fed dragons as party curiosities, or as a way to pick up women. Because everyone knows that women love cute animals, especially those that can be trained to toast bread in the mornings.

The lack of thumbs makes it difficult for them to spread butter and jelly, though.

The humble bearded dragon is quickly replacing the ‘tiny dog’ niche in Western society, and pet accessory companies are beginning to churn out little sweaters and other clothing for these easy-to-freeze animals. It won’t be long before bearded dragons are found clinging to the insides of purses and wearing ridiculously large sunglasses for comedic effect. The only difference, thankfully, is that bearded dragons don’t yap incessantly at everything within 20 yards of themselves.

Some have already taken the initiative to start taking their bearded dragons on walks, as terrariums are cramped and boring. Bearded dragons are naturally athletic animals, and enjoy bounding around on the lawn or sidewalk and exercising their muscular, albeit stubby, legs. Given their regal genetic history, I can’t help but wonder if some part of them finds this treatment insulting to their dignity, if they realize how far they’ve fallen.

How to Demean Your Dragon

So the monsters of lore are gone from us, despite a grand and heart-scorching tale of evolutionary ingenuity and might. All that remains is a disgusting carrion eater the size of a deer, and a chunky, scruffy-faced Aussie lizard that under the right circumstances, might be able to light your cigar for you. Embrace the fact that you don’t share this planet with the extinct, flying terrors of the Mesozoic. Things would be a lot harder for you, I can guarantee it.

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.


4 thoughts on “Dragons

  1. as a mature student for my gcse biology – evolution, I thought it an excellent idea to look into bearded dragons (I have one) saw and read your article thinking oooh this could be good – and that it was – I did laugh quite a lot infact……. not sure how reliable any of it is or that I can or should
    include any of it into my submission but was def an interesting read lol

    • Well, I’m glad you had a laugh, even if this wasn’t quite what you were looking for! 🙂
      Given that this was an April Fool’s entry, I cannot responsibly condone using pretty much any bit of information contained in this blog post as factual….well…besides the fact that Postosuchus was a real animal, and that bearded dragons and Komodo dragons exist as real reptiles. Everything else is pretty much truth-deficient, barring the underlying biological mechanisms that could, theoretically, lead to the evolution of a clade of “dragons.”

  2. Pingback: On the Origin of Species – Yungoos and Gumshoos – Spiders and Science

  3. My personal theory is that dragon breath was originally less flame more smoke and evolved as a defense against wing parasites. Later it was co-opted for combat between dragons and later still as a hunting tool, by which point dragons could no longer smoke out wing parasites without severely burning themselves. Now all dragons have permanently itchy wings, which explains the bad temper.

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