Draconology: The Draconimorpha

Draconology © VikasRao

Please do not copy, redistribute, reference, trace, reuse, alter or modify for your own use without my prior permission, thank you!

Despite their superficial resemblance, the Draconimorpha are not particularly closely related to any other clade of modern reptiles. They are in fact, members of the Parareptilia, a subclass of Reptilia which also includes the now extinct Pareiasaurs among others, and are quite distinct from the more familiar Eureptilia, which includes the lepidosaurs (tuataras, lizards & snakes), archosaurs (crocodiles & birds) and the testudines (turtles and tortoises).

While the vast majority of the Parareptiles died out during the Great Dying (aka the Permian-Triassic mass extinction) 252 million years ago, the draconimorpha endured.

Interestingly, not all the taxa within this clade appear to be very closely related, and it's likely that there are several other (now extinct) taxa whose discovery might help better resolve their phylogenetic relationships.

The surviving members of draconimorpha can be classified into 5 distinct clades: Thalattophidia (sea serpents), Ophiosuchoidea (wyrms), Volanosauria (wyverns), Therosuchia (Drakes) and Draconia (dragons).

Sea serpents (Thalattophidia): These marine reptiles are basal draconimorphs that do not appear to be very closely related to any of the other clades, indicating that they may not share a common ancestor. With just 11 known species, the sea serpents are a very poorly studied lot. This of course isn't surprising considering that most of them are either benthic or pelagic, and thus rarely seen. Unlike snakes, most of which have long bodies but short necks and tails, sea serpents have uniformly elongated bodies, with long necks, bodies and tails, and 4 limbs that are modified into flippers. In most species, these flippers are quite short and function solely in stabilizing their bodies while swimming. As with some sharks, sea serpents appear to be mesotherms or regional heterotherms, being able to keep certain regions of their bodies at temperatures above that of the surrounding water thanks to the presence of countercurrent heat exchangers.

Reaching lengths of upto 22m, and weighing upto 7 tons, the largest known sea serpent is without doubt the greater sea orm or Jormungandr (Poseidonophis titanis). While sightings have been reported worldwide, virtually nothing is known about this animal's ecology as it spends much of its life in the deep ocean.

The clade (magnorder) Draconiformes includes the 4 remaining clades, and appear to have all descended from an as of yet undiscovered common ancestor that lived around 255 mya during the Late Permian period, as revealed by molecular clock studies.

Wyrms (Ophiosuchia): Often called “snake dragons” and more rarely “scaly salamanders” due to their primitive-looking, newt/salamander like morphologies, wyrms aren’t particularly closely related to dragons and drakes despite a strong resemblance to some of the latter. Most notably, wyrms have a sprawling gait similar to that of most lizards, whereas all drakes have an erect gait similar to mammals with their limbs being positioned underneath their bodies. There are 287 known species in 7 families, making them the most speciose clade of the draconimorpha, and contrary to popular belief, all known wyrms possess legs, unlike snakes, but individuals often have a limb or two missing as a result of predation, intraspecific combat or both. Like snakes however, several species of wyrms are venomous, delivering venom via grooved teeth similar to those of Helodermatids (Gila monster & beaded lizards). Unlike Helodermatids but like snakes though, the venom glands as well as the venom-delivering teeth are located in the upper jaw, and while most species are considered harmless, a few do have venom powerful enough to fell a human.

While most wyrms are quite small, the giant ash wyrm (Ophiosuchus cinereus) of South America is a notable exception. Growing to 5.5 - 6.5m in length, it is roughly as long as a large Nile or saltwater crocodile, but due to its slenderer build, isn’t as massive, weighing roughly 250-300kg, with both sexes being similar in size. 

Wyverns (Volanosauria): Wyverns are flying reptiles representing the youngest clade of Draconiformes, having appeared roughly 28 million years ago. Despite bearing a superficial resemblance to dragons, wyverns aren't very closely related to them, and are instead believed to have shared a common ancestor with the wyrms, although as flying animals, they have much higher metabolic rates, comparable to that of some mammals but less than that of birds. Many wyverns are sexually dimorphic, with males often having ornate integumentary structures, from spines & crests to frills and dewlaps, although in all known species, the females are larger than the males. With 130 species known from 5 families, wyverns are among the most diverse groups within the Draconiformes. The general morphology of wyverns is vaguely similar to that of a large bat, but with only 4 digits on their winged forelimbs, 2 of which are elongated and support the patagium, and much shorter tails than most dragons. Their bones also lack the pneumaticity seen in dragons, which ultimately prohibits them from growing as large. Wyverns possess plantigrade hindlimbs and digitigrade forelimbs, similar to the ancient pterosaurs, in contrast to dragons whose hindlimbs are digitigrade as well, and many are facultatively bipedal. Most wyverns are crepuscular or nocturnal, a strategy that likely evolved to minimize competition with birds, and as with wyrms, many also possess venom, but have a more advanced and efficient mode of delivery, with multiple pairs of hollow fangs in the upper jaw. 

Although most wyverns prey on insects and small birds or bats on the wing, the New Guinean giant wyvern (Haplorhynchus pennocristatus), with its 3m wingspan and powerful jaws, is an aerial apex predator. 

Towards the end of the Permian, when the Parareptiles were beginning to decline, the Draconiformes underwent a split that gave rise to 2 distinct lineages: one gave rise to the wyrms and later the wyverns while the other gave rise to the Pyrosauria, the group that comprises the drakes of the order Therosuchia and the dragons of the Draconia clade. These reptiles get their name from an astonishing and unique trait - by combining certain endogenously-produced pyrophoric compounds in a “reaction chamber” located in the throat and then forcibly expelling it outwards, they can produce fire. This ability appears to have originated in the common ancestor of all extant pyrosaurians, but has since been lost, retained and modified in several groups.

Drakes (Therosuchia):  Often called “wingless dragons”, drakes are large reptiles that are in fact closely related to dragons, and like them, certain species can breathe fire, though this ability isn’t as developed as it is in the latter, and several species have lost it altogether. There are 20 species of drake in 4 families, making them the least speciose clade of Draconiformes, even though they are found in every continent except Antarctica. Half of these species are largely aquatic, with the majority of them being marine reptiles. The terrestrial species range from sleek, almost dromaeosaur-like forms to heavily-built, rauisuchian-like forms. While most species are predators, there are some omnivorous and herbivorous taxa. Interestingly, drakes have a pillar-erect gait, wherein the hip socket faces downward to form a bony “shelf” with which the femur articulates. The only other clade of vertebrates known to have had such a configuration were the Rauisuchia, which were completely unrelated. It also appears to have been present in early dragons, though no extant taxa have retained it. Drakes also differ from wyrms and wyverns in their breathing mechanism: while the 2 former groups utilize a “visceral pumping” mechanism wherein abdominal muscles push the viscera in order to expand the lungs, drakes have a muscular diaphragm analogous to that of mammals that allows them to ventilate their lungs more efficiently. They also have a unidirectional air-flow system like birds, crocodiles and monitor lizards, but with a very different anatomy. These traits allow them to maintain a much higher metabolic rate than most reptiles, but nowhere near as high as that of most mammals, thus making them mesotherms at best. 

The largest drakes are big enough to maintain near-constant body temperatures via gigantothermy, and the best example of this is the enormous titan drake (Dirosuchus maximus). Measuring 13-16m in length and weighing an impressive 5-7 tons, these marine reptiles are roughly the size of Tyrannosaurus rex, and are the largest members of the Draconimorpha and by extension, the largest extant reptiles. 

The clade Draconia includes a large number of medium- to large-sized, mostly flying reptiles that are often referred to as dragons. While not all can breathe fire, evidence of their relatedness can be found in several anatomical features, such as: 

• Forelimbs modified into wings, with digits III-V being elongated to support an expansive patagium and digits I & II being shorter and adapted for weight-bearing,

• A fused radius and ulna, as well as fused and elongated carpal (wrist) bones,

• High metabolic rates comparable to that of mammals and birds,

• A covering of heat-retentive integument, known as coelofibers or colloquially, “dragon fur”,

• A complex respiratory system comprising several air sacs in addition to the diaphragm mechanism seen in drakes,

• Highly pneumatised bones, and

• An extremely complex brain that affords unusually high intelligence on par with mammals and birds.

While Draconia is a monophyletic clade, with all extant and a number of extinct taxa having evolved from a common ancestor, the differences between these taxa has led to the group being further divided into 2 orders: the Ornithodraconia (bird dragons) and the Eudraconia (true dragons).

Gryphons and kin (Ornithodraconia): This order includes a number of species that bear a superficial resemblance to birds, and are thus sometimes called “bird dragons”. The best-known examples include the griffins, cockatrices and pegasi. The most notable trait these groups share is the fusion of the rostral scales and skin to form a beak, which, although may appear bird-like, is anatomically more similar to that of turtles. They also have longer wrists and shorter tails than the true dragons, and most have a dense covering of coelofibers. Ornithodraconians have lost their ability to breathe fire, and while a handful few have retained some vestiges of it, none can truly produce flame in the manner of some drakes or the true dragons. Many are herbivorous or omnivorous, and only a few are predators. With 49 species in 4 families, they aren't as diverse as the true dragons, but were certainly more diverse in the past, with over a 100 species represented in the fossil record, a sign that their lineages are declining. This is likely due to competition from mammals and true dragons, and the majority of extant species are found primarily on isolated islands where the aforementioned competitors are few or non-existent altogether.

Absence of competitors has allowed some species to grow to rather large sizes, such as the giant kirin (Giraffadraco limuriensis) of Lemuria, which sports a wingspan of 9m and, standing over 4m tall, is nearly as tall as a giraffe.

True dragons (Eudraconia): More often than not, the term “dragon” refers to the members of this clade. With 68 species in 4 distinct families, true dragons are the third-most speciose clade of the draconimorpha. They stem from a more basal lineage of dragons, and have retained many of their ancestors’ reptilian traits. Most notably, they have refined their fire-producing ability to the point where they can use it as a deadly offensive weapon and an insurmountable defense. All true dragons possess teeth, have longer tails, shorter wrists, and a different bone structure compared to their griffin cousins. While they appear to be covered in reptilian scales, these are in fact modified coelofibers, and are structurally and compositionally very different from the scales of other reptiles. In fact, a closer analogy would be pangolin scales, which are formed in a similar manner. The most likely explanation for this modification is that these “scales” are tougher and thus offer much better protection against attacks by other dragons, whereas the fur-like coelofibers would simply be burned off, and still manage to conserve body heat quite well. Baby dragons, known as “flaplings”, are actually born with a coat of coelofibers, but this is replaced by a covering of adult dragon scales roughly around the same time they begin to breathe fire. Barring one exception. all dragons are obligate carnivores, and the vast majority of them are known to burn their kill before consuming it. This makes the meat much easier to digest & kills toxic microbes, which allows true dragons to make due with much shorter and less complex digestive systems than most carnivores of similar size, which in turn allows them to save a considerable amount of weight. While the ornithodraconia have hollow bones with a thin-walled honeycombed structure similar to that of birds and pterosaurs, eudraconians have bones that are filled with numerous pits and hollows invaded by air sacs, a structure that is similar to that of the giant azhdarchid Hatzegopteryx, but unlike those of any other extant flying animal. This makes the bones extremely sturdy and stress-resistant as well as extremely lightweight.

Another notable trait of true dragons is their remarkably high intelligence, on par with that of cetaceans, elephants and in some cases even primates.

Many dragon species pose a major threat to humans, but none more so than one of the largest, the enormous Eurasian mountain devil (Magnadrakon imperiosus). With a wingspan of 13.5-15m and standing over 5m in height, this dragon is the size of a small aircraft and can look a giraffe in the eye.



Edit: Updated the image with better lighting and to reflect the updated appearances of everything. Before anyone asks:
1. No the titan drake did not get nerfed. I just corrected its posture because I realized that if something this size tried to stand fully upright like a human it would break its own spine.
2. The giant kirin did get a "minor" redesign.