Dragons probably originated as one of many branches of the reptiles, no later than 200,000,000 years ago in the late Triassic. This was a period of great reptile diversification, during which emerged some of the most successful reptile groups, in terms of both abundance and diversification. Dragon evolution echoes the evolution of the archdiocesan of the time. Dragons took to the air, as did the pterosaurs, and became aquatic, like the plesiosaurs — ancestors of modern crocodiles and birds. If you will, imagine the dragon family tree…

The Prehistoric Dragon

Cretaceous dragons were the largest flying animals ever to have lived. The prehistoric dragon descended from a group of aquatic or semi-aquatic dragons that occupied coastal swamps approximately 200 million years ago in the late Triassic, which gave rise to both marine and terrestrial species. Initially, the terrestrial dragons were quadrupedal, running on all fours and unable either to fly or to breathe fire. One species evolved the ability to run bipedal, on its hind legs. This enabled further evolution of the forelegs, which were no longer used for standing or running. These limbs eventually evolved into wings, making flight possible. This parallels almost exactly the evolution of birds with flight ability from small, bipedal dinosaurs.

At some stage — and there is no fossil evidence on this point to date — dragons harnessed active gut bacteria to produce hydrogen. This made it possible for dragons to escape the size restrictions of bird and bat flight, and to evolve into the largest flying animals ever to exist, challenging one of the largest known carnivore on land at the time, theT. Rex. Subsequently, dragons ingested inorganic minerals, such as platinum, sparking the catalytic ignition of its gut-produced hydrogen. The potent weapon of fire-breathing was added to the dragon's armory: the prehistoric dragon had arrived.

Prehistoric dragons bore conspicuous curved horns, larger in the male than in the female. These were important weapons in fights over territory, and also served as a form of display to deter rivals, if possible: directly analogous to the antlers of deer. The best estimate of the size of late Cretaceous dragons is that they weighed in excess of a ton, and had a wingspan upward of 35 feet. For comparison, the largest known carnivorous dinosaur, Tyrannosaurus Rex, was around 40 feet in length with a weight in the region of 6 tons.


A flying dragon weighed considerably less than an earthbound dinosaur of the same size. A dragon's bones were not solid, rather like the hollow bones of the modern bird. This reduced the weight of the skeleton without sacrificing strength, a necessary adaption to flight. The wings of the dragon were similar in structure to those of bats, the bulk of the aerofoil surface being a relatively tin leathery membrane of skin supported by the long bones of the limb and extended bones of the digits.


To improve the efficiency of flapping flight, the bulk of the pectoral flight muscles were located on the animal's thorax rather rather than in the wings themselves. As the flight muscles contracted, would be moved downward (the power stroke of flight) by pulling on tendons: the mass of the flight muscles themselves would not have wasted energy by moving themselves up and down relative to the body with each wing beat. (All subsequent flying vertebrates us a similar "fly by wire" system).


Flight was possible largely of the presence of large paired flight bladders, filled with hydrogen produced by the activity of symbiotic bacteria within the dragon's gut. Also, a dragon's bones were not solid, but were honeycombed with gas spaces, rather like the hollow bones of modern birds. This reduced the weight of the skeleton without sacrificing strength, a necessary adaption to flight. In the case of the dragons (but not of birds), the spaces within the bones have been filled with hydrogen, further reducing weight. Accumulation of hydrogen within the flight bladders meant that the dragons could increase in volume quite rapidly as the bladders expanded: the dragons could also contract the bladders by venting gas, perhaps as a means of controlling altitude (like modern hot air or helium balloons), or by combustion during fire-breathing.


Which brings me to my next point, fire-breathing in dragons was based on production of copious amounts of combustible gas, principally hydrogen. This probably evolved initially to facilitate flight. The hydrogen was actually produced by bacteria resident in the dragon's gut: all vertebrates have an abundant gut flora, often crucial to digestion and other physiological functions. In laboratory conditions, certain bacteria can produce gas consisting of as much as 60 percent hydrogen.


Different strains of gut bacteria could also produce methane, which is combustible. Simple ignition of either hydrogen or methane in air only produces a weak flame. The powerful jets of flame emitted by dragons indicate that burning gas was released under pressure, evidently much higher pressure than what could have been produced by contraction of the thorax during normal exhalation. There may have been a special mechanism involved, reservoir organ in bombardier beetle, which spurts an explosive jet of hot chemicals to deter it's enemies.


The skin of the dragons of the Cretaceous, like that of almost all reptiles, was covered in scales and made largely of the tough and water-resistant protein keratin. The dragon's skin color and pattern functioned as camouflage, warning coloration or as social signals. Juveniles would be vulnerable to attack while on the ground, particularly when they were too young to generate sufficient hydrogen to fly and to breathe fire. They were conspicuously colored when at rest, but if disturbed used warning colors as a deterrent. A young dragon threatened by a predator reared up, inflated it's lungs and flight bladders as far as possible, and raise it's wings to flash bright patches of color on the underside of the wings, as a warning to it's attacker. Accompanied by loud screeches, this display must have been terrifying, enough to put off all but the most persistent tyrannosaur.


In adults, bright colors and conspicuous patterns would be used to communicate socially, as displays to attract mates, threaten rivals, or to deter territorial encroachment. Young males - so-called "bachelor males," vying for territory and mates - - were typically a vibrant red in color, while older, territory holding males were darker. Some modern reptiles, such as chameleons, can rapidly change color. Dragons may also have had this ability. Rapid changes in color would enhance warning displays, and the ability to change the color of the back and upper wing surfaces to white would have reduced solar heat gain in flight and mitigated the potential overheating problems of a large active flying animal.



The Marine Dragon

Before prehistoric dragons, some of the early dragon species were aquatic or semi-aquatic, foraging in coastal swamps and the shallow sea, living, in fact, rather like modern crocodiles. When a cataclysmic mass extinction (the KT extinction) occurred about 65 million years ago, eliminating dinosaurs and terrestrial prehistoric dragons, these aquatic dragons survived. A fortuitous mutation gave these dragons a third pair of limbs, supplementing the previous two and making them a new unique kind of vertebrate, i.e., a six-limbed animal.


Some of these new dragons recolonized the land, occupying a world vacated by dinosaurs and earlier dragons. In these terrestrial dragons, the supplementary limbs evolved into the fully functional wings of flying dragons. Other dragons stayed aquatic, specializing more and more in marine food resources — crustaceans, fish, turtles — caught in shallow coastal waters. As time passed, they adapted to a fully aquatic life, the rudimentary wings becoming fins.


The clawed limbs of terrestrial dragons were of little use in catching fish, so these evolved into flippers, like those of modern turtles. Fish were trapped in the dragon's jaws, which became larger and longer over the course of generations, and their jaws were armed with large numbers of spike-like teeth for holding their slippery prey. Wings, of course, were useless impediments in the water, and eventually dwindled and disappeared. The most celebrated example of the sea dragon may be the Loch Ness Monster.


Freed from the limitations of gravity, marine dragons evolved to be of considerable size, and some may have reached more than six hundred feet in length. The body was more sinuous than that of the terrestrial dragons. Propulsion through the water was primarily by side-to-side undulations of the body, with the flipper like limbs used for maneuvering, rather than thrust, like the fins of modern sharks. The neck was also long and flexible, to enable rapid snatching at prey.


The mouth and jaws were relatively larger than terrestrial dragons, and were armed with a large number of spiky teeth for holding their slippery prey. Its nostrils were high on the snout, so breathing was possible without more of the animal surfacing than was absolutely necessary. (Modern crocodiles share this adaption.) The nostrils were sealed by a flap of skin during dives, and underwater feeding was made possible by a flap separating the mouth from the breathing passages. (This structure played an important part in enabling fire breathing in terrestrial dragons.)


According to some accounts, sea dragons had a pair of horns a "collar" or neck frill, possibly used in display, like those of the terrestrial species, e.g., the prehistoric dragon. While the dragon was swimming, the neck frill folded flat to reduce water-resistance. Sea dragons probably spent much of their time, when not actively diving for food, basking at the surface. Their backs likely had a "mackerel" camouflage pattern to make them conspicuous in light coming down vertically from the surface.

Wings, of course, were useless impediments in the water, and dwindled and disappeared over time. Marine dragons had relatively small limbs, functioning partly as legs for moving rapidly along the bed of a river or lake, partly as fins during swimming. The third pair of legs were mainly used for fins. Propulsion through the water was primarily by side-to-side undulations of the body, with the flipper like limbs used for maneuvering, rather than thrust, like the fins of modern sharks. Aquatic dragons could neither fly, or breathe fire. The "flight bladders" were of some use in adjusting buoyancy when the animal swam in deeper water. They came out unto land at the water margins, and generally lived like modern otters or crocodiles.



The Forest Dragon