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Dragon Phylogenetic Classification

~ Introduction
~ Domain to Phylum
~ A variable number of limbs
~ Reptilian ancestors
~ Convergent evolution?
~ Phylogenetic tree
~ Conclusion


Introduction:
Phylogeny: The development or evolution of a kind or type of animal (Concise Macquarie Dictionary, 1982, Doubleday Australia Pty. Limited). Phylogeny can also include taxonomic classification.
The purpose of this essay is to classify the dragon in both taxonomical and evolutionary terms. The main types of dragons that will be classified are as follows:

- Western dragon (four legs, wings either membranous or feathered)
- Eastern dragon (four legs, wingless)
- Faerie dragon (four legs, either one or two pairs of wings)
- Water dragon (four flippers, wingless)
- Dragoon (bipedal, four legs, two wings)
- Wyvern (two legs, wings either bat-like or pterodactyl-like)
- Wyrm (legless and wingless)
- Drake (four legs, wingless)
- Amphithetre (legless, feathered wings)

The dragon races that have multiple heads or other such ridiculous attributes, such as the Hydra, Amphisbaena or Naga will not be addressed in this essay.

For those not familiar with the classification scheme (first proposed by Carlos Linnaeus- who incidentally Latininsed his own name as if to classify himself!), it is explained below.
The main point is to lump organisms together into increasingly larger, more inclusive groups, using a hierarchical method of classification (Strickberger, 2000). Each step up this hierarchy contains more and more organisms, that are more distantly related to each other (ie. their common ancestor, from which they all evolved, is more and more ancient). (The more fundamental a feature is to a group of organisms, the earlier that feature evolved.)
The usual hierarchy is as follows:

- Species: animals that are most closely related to each other and can interbreed with fertile offspring.
- Genus: (plural- genera) groups of closely-related species. These can sometimes interbreed but the progeny is usually sterile (ie. a mule).
- Family: a group of related genera.
- Order: a group of similar families.
- Class: a group of orders that show similar characteristics.
- Phylum: (plural- phyla) a group of classes, although by this stage the features they share in common would be very fundamental.
- Kingdom: a group of phyla.

There are often also sub-phlya, sub-classes, superfamilies, etc(1*).

Domain to Phylum:
A relatively recent level of classification is the domain of life that an organism falls into. The level of the domain separates the Bacteria, Archaea and Eykaryotes. It also gives the bacteria and archaea a bit more importance, instead of classifying them at the same level as multicellular organisms, which they far outnumber both in terms of species diversity/ number and biomass(2*). The dragon is of course multicellular, and is a eukaryote. A eukaryote is an organism whose cell/s exhibit complexity in that they have a membrane-bound nucleus and organelles, as well as large cell size in general (Alberts et al., 1998).

Dragons have been further classified into the Kingdom Animalia. This should be relatively self-explanatory. Basically, animals rely on plants or other animals for food (heterotrophy) and cannot manufacture their own food (autotrophy) (Strickberger, 2000). Animals are also motile, that is, they can move around to better respond to environmental fluctuations. The Kingdom Animalia contains multicellular animals, ie. a jellyfish (phylum Cnidaria). The Kingdom Protozoa contains unicellular animals(3*), ie. a Paramecium (a ciliophorate).

Multicellularity has a lot of advantages. It allows for specialisation, ie. the formation of tissues and organs, each performing a different function. It also allows for greater size of the organism as a whole. Single-celled animals can only reach a certain size, or else their surface area to volume ratio is greatly affected (the more surface area an organism presents to the environment as compared with its overall volume, the more efficient its nutrient uptake). Also, multicellular animals can move much faster and thus their response rate to fluctuating conditions is increased correspondingly (Strickberger, 2000).

The dragon can further be classisifed into the Phylum Chordata. These animals have a hollow dorsal cord (like our spine), with a nerve cord (our spinal cord) running just above. They also possess gill slits at some stage/s of the life cycle, usually during embryogenesis (the more formative stages of growth and development in the embryo) (Mader, 2000).

A variable number of limbs:
Here, the dragons have been given their own class, Draco. Draco is Latin for dragon, and most phylogenetic names are Latinised or in Ancient Greek. Even though dragons have the outward appearance of a reptile, they have been placed into their own class for the following reasons:
Reptiles today are all ectotherms(4*), that is, they cannot regulate their body temperature internally but rely on external heat/ cooling sources instead. They are not "cold-blooded" as is commonly thought.
Reptiles also have a three-chambered heart (with the exception of the crocodile family, Crocodylia). Dragons have a fully developed four-chambered heart just like a bird or mammal. Furthermore, all living reptiles walk with their legs sprawled outwards, unlike dragons which walk with the legs tucked underneath the body (Benton, 1998).

Dinosaurs may had had all these features too, however dragons also have anywhere between 0 and 8 limbs, and breath weapons, which makes them vastly different from other vertebrates including dinosaurs.

Here, the myth of the dragon gets "in the way" of an effective classification. A wyrm and a Chinese dragon are the same type of animal, as is a Faerie dragon. These animals all differ in so many ways, especially with the number of limbs they have. Yet they are all dragons. It's like lumping snakes with lizards. Part of the dragon's beauty lies in its diversity, although this makes it far more complicated to classify.

This is the main reason why dragons have been given their own class, as simply giving them an order under the class Reptilia probably wouldn't be sufficient in describing their variability. Instead, the different dragon orders are based on the number of limbs the dragon has (limbs= legs + wings) and the type of dragon it is. This seems a logical way of putting it. Another way would have been to lump the Western dragons together, the Easterns together, etc. This would result in Drakes and Wyverns being more closely related to each other than Drakes and Chinese dragons. Drakes and Chinese dragons both have four limbs and no wings, whereas Wyverns have two wings and two legs. Both methods have their flaws, however there is no way of telling which is the correct method as there are no dragons to test the theories on!

However, a phylogenetic tree is not interested solely in classification; that in itself can be rather dull. Phylogenetics is also interested in evolution, so where did the class Draco originate from?

Reptilian ancestors:
For starters, the dragon wouldn't have evolved from the class Mammalia. If it had, then it must have taken a few evolutionary backsteps. For instance, mammals have a very efficient, highly insulating body covering: hair (Strickberger, 2000). The whole process of evolution is that originates through chance mutations, whereby some individuals of a species have features that allow them to survive and reproduce more successfully than others. Thus they pass on their genes, and their successful features, whereas other indivuals, less adapted to the environment, die off without reproducing (Mader, 2000). It is highly dubious that a mammal-derived dragon that has evolved to have a scaly hide would be better adapted to the environment than its furry neighbour. In fact, evolution would probably push for the extinction of these non-furred dragons in most circumstances (depending on the environment).

It is for a similar reason that dragons couldn't have evolved from the class Aves. Birds have an even more effective insulator than hair; they have feathers covering almost the whole body. Feathery wings make perfect aerofoils when viewed in cross-section (Attenborough, 1980), whereas the overall aerodynamics of a leathery dragon wing pale in comparism.

Dragons tend to display more features of an extremely advanced reptile than a mammalian or avian throwback, therefore they probably evolved from a reptilian ancestor. They have differentiated teeth, an upright stance, a reduced number of digits on fore and hindfeet, an endothermic metabolism; all of which reptiles in the form of dinosaurs had (or may have) evolved. This doesn't mean necessarily that dragons evolved from dinosaurs, just that reptiles have the capacity for advanced features more at home in the mammals, and so a quadrupedal reptile is the most logical possibility for a Draconic ancestor.

Convergent evolution?:
Here we will explain the confusion that can arise when attempting to classify dragons, citing the Faerie dragon as an example.

Faerie dragons come in two varieties: with one pair of butterfly wings or two. From an evolutionary point of view, this could come about in two main ways, and which one it is would decide how the dragon is to be classified. No-one could ever say for sure exactly how to classify an organism such as this- it has no fossil record to speak of, and as it is a mythical creature, there is no way to conduct DNA tests using molecular techniques either!

The first way is by convergent evolution. This is when two unrelated animals look the same, but only because they have both adapted to the same environmental niche (Strickberger, 2000). The most famous example is sharks and dolphins; both are fast, predatory marine creatures, however one is a fish and the other a mammal. As a result of their similar lifestyles they look the same. The same could be said with the Faerie dragons. The dragons with two pairs of wings may be an ancient lineage that has changed very little during the eons. The dragons with one pair of wings may be closer related to the Western dragon (they have the same number of wings and are phenotypically almost the same animal, just in a different size). The second group of Faerie dragons may have evolved to look similar to the first group because they live in the same habitat and hunt the same prey.

The second way that Faerie dragons may have come to have different numbers of wings is that originally, all Faerie dragons had two pairs of wings. After a while, the hind pair were reduced and disappeared altogether(5*). There would have to be an evolutionary advantage (or at least a neutral effect) for the dragon to lose the hind pair, such as not needing as much energy to fly as they only have to power half the number of wings (although there is less wing surface area left to provide lift). If this is the case, the new two-winged dragons must have been able to co-exist with the four-winged type so as not to drive them to extinction.

If the second theory proposed above is correct and two-winged Faerie dragons evolved from four-winged dragons, it must have happened so long ago that they are distantly related enough today to be considered separate. However, this still doesn't mean that they are more closely related to other six-limbed dragons (ie. the Western) than to the four-winged Faerie dragons.

The two varieties of Faerie dragon have thus been placed in separate orders, separate them from other six-limbed dragons. The reason for this is because both types of Faerie dragon have the same type of wing, a chitinous butterfly-type wing. If two-winged Faerie dragons had evolved from Western dragons, it seems exceptionally unlikely that they would revert from the bat-type wing to the inefficient butterfly-type wing. Therefore they are being separated from all other dragons and from each other, despite the fact that the four-winged variety probably gave rise to the two-winged variety. As stated above, this evolutionary process happened long enough ago for the two Faerie dragon types to be considered separate and classified into different orders.

Phylogenetic tree:
Here a diagram of a typical phylogenetic tree showing the class Draco has been created (fig. 1).


Fig. 1: Scaled phylogenetic tree (cladogram) of the Animal class Draco: Eukarya: Animalia: Chordata: Vertebrata: Draco

Note: To keep this diagram as simplified as possible, only the major families of dragons have been included. This diagram does not delve into genera. Latin names have not been assigned to each dragon family as this would further complicate things and be of very little, if any, relevance.

When reading a phylogenetic tree, it may be easier to start from the right-hand side. The names along the right represent the different dragon families, and the length of the horizontal lines inter-connecting them is indicative of the amount of time that separates those two families of dragons. The most ancient of seperations can be found on the left-hand side of the diagram. Therefore, the Dragoon and Western dragon (with membranous wings) diverged relatively recently from each other as one took to a bipedal stance. The two dragon groups that would eventually evolve feathered wings (Western dragon and Amphithetre) diverged from the other Western-type dragons further back into the past.

Moving to the left-hand side, we see that the first major split in the class Draco occurred when the Faerie dragons split off into their own sub-class, made up of two orders- each consisting of one family. The next dragon order (again consisting of a single family) to branch off were the Water dragons, then all the dragons that would remain wingless, and so on. The line that appears on the far left indicates the common ancestor to all dragons.

For Fig. 1, the assumption has been made that a more inefficient wing type is a result of that type being more ancient. Therefore, the Faerie dragons with two pairs of wings are placed as the oldest dragon type, as the butterfly-wings they have are very inefficient. All the other winged dragons evolved from the Wyvern (with pterodactyl-type wings), and later developed the typical bat-type wing. The last type of wing to evolve included feathers, as this is the most aerodynamic wing of all. Dragons with feathered wings (Western dragons and Amphithetres) would most probably be completely feathered, the former retaining its legs while the latter sacrificing them for increased streamlining, undoubtedly evolving a long muzzle in the process in order to catch prey on the wing.

It should be mentioned that, although dragons with more than four limbs have been included, in reality no vertebrate has ever had more than four. If dragons roamed the skies today, the Wyvern would be most likely all you would see (not that that wouldn't be rewarding!), and the Eastern dragons on the ground. Regarding the feathered-winged dragons, feathers are typically the mark of a bird (class Aves), although some dinosaurs probably possessed them. These dragons, were it not for their breath weapon and extra limbs, could just as easily fit in with the avians or the Archosaurs as in Draco.

Note: a typical phylogenetic tree uses mainly genetic markers (hence the name phylogenetic!) to classify evolution of species, however we obviously don't have the luxury of available dragon genetic information. So, this really is an educated guess. A fair amount of time has gone into planning this tree, so you can be assured it is by no means haphazard. Although we feel this is the most logical classification of the dragon, there are probably multiple ways it could have been achieved.

"Technical" notes:
Although the cladogram is illustrated in the typical molecular phylogenetic format, this is impossible for the dragon and so it was derived using morphological means only. It was diagrammed this way as the typical morphological cladogram cannot map time differences between nodes, whereas for obvious reasons, the molecular cladogram can illustrate divergence times. Making assumptions on divergence times based on morphology of "extant" forms may be folly, however as the dragon is a mythical creature it simply serves to add an extra dimension to the diagram. In Fig. 1, the sister taxa may be grouped as follows: Dragoon with Western dragon/ membranous wings; Western dragon/ feathered wings with Amphithetre, etc.

Conclusion:
It is hoped that this essay has conveyed a greater understanding to the reader about the evolution of the dragon, or at least introduced some new, hopefully interesting, concepts. Although an essay of this type about dragons could never hope to be 100% accurate, we hope it at least partially achieved this. If dragons were alive their evolution may have followed a similar path to the one proposed above.
The reason that the dragon is only separated at the family level and not at the genus or species level (in fig. 1) is that the dragon itself is such a subjective creature, and there are countless portrayals of it. As such, there are also no wrong answers when it comes to classifying it.

1* Here is an example of the classification in use:

- Species: Canis familiaris (the lovable domestic dog).
- Genus: Canis, including dogs, wolves, coyotes, etc.
- Family: Canidae, including the genera Canis as well as others such as Vulpes (foxes).
- Superfamily: Canoidea, (dog-like carnivores) includes canids, bears, mustelids and procoyonids, that all differ from other (cat-like) land carnivores by several anatomical features. (Bay Books, 1972.)
- Order: Carnivora, (mostly) meat eating-animals, including not only the canids, but ursids (bears), mustelids (weasels, stoats, wolverine, etc) and other families of carnivorous mammals.
- Class: Mammalia, animals that possess mammary glands, are endothermic, and are covered in hair or fur.
- Sub-phylum: Vertebrata, the notochord in Chordates in replaced in adults by vertebrae made of bone or cartilage (Strickberger, 2000).
- Phylum: Chordata, possess a hollow dorsal notochord, nerve cord, post-anal tail, and gill slits during embryogenesis.
- Kingdom: Animalia, multicellular eukaryotic organisms.
- Domain: Eukarya, organisms with membrane-bound organelles in the cells.

2* Bacteria and archaea used to be classified in the Kingdom Protista, which put them at the same level as the plants (Kingdom Plantae) and the animals (Kingdom Animalia).
Bacteria and archaea differ from eykaryotic organisms in that they have a much simpler cellular structure, with a single circular chromosome, no membrane-bound nucleus, mitochondria/ chloroplast or other organelles, and the size of the cell itself is also smaller. They can also be termed prokaryotes. All Bacteria and archaea are unicelluar. They also differ from each other in a variety of ways.
3* The term "animal" is applied very loosely here, as "animal", strictly speaking, applies to multicellular organisms.

4* Palaeontologists have been debting for ages the theory of dinosaurs being endotherms, like mammals or birds, and the jury is still out on the verdict. One of the most vocal debaters for endothermy is Robert T. Bakker, with his famous book, "The Dinosaur Heresies".

5* This reduction of the second pair of wings is visible in insects. Some, such as flies and mosquitoes (order Diptera), have the second pair reduced to a pair of knobs called halteres which aid in flight (Pinchin, 1986).

Post je objavljen 10.02.2006. u 00:28 sati.