Wyverns are complex animals that have many adaptations that are lacking in other animals. They are theropods like birds and are well-adapted to flight. They are also able to spit fire at enemies and prey, a feature unseen in any other animal.
The head of a wyvern is much like those of other theropods’ heads. Wyverns have long snouts filled with teeth for tearing at prey. There are groups of long feathers behind the ears called the fan feathers. These feathers look like ears but they have no auditory function. These fan feathers are typically held against the head pointing back. They are brought forward and splayed out like a fan as a threat display. The fan feathers are often brightly colored.
The most distinguishing feature on a wyvern’s head are the horns, or more accurately, crests. Each wyvern has two horns on the head. The first horn is located near the tip of the snout and is the smaller of the two. The second horn is a sagittal crest that is located at the base of the snout just in front of the eyes. The crests are thin and blade-like. The nose is located at the base of the sagittal crest instead of the tip of the snout as in most animals.
The eyes are large and face forward for excellent vision. This allows wyverns to spot prey from afar. The pupils are long like a crocodile’s.
The forelimbs of all wyverns are wings to allow them to fly. They are feathered like a bird’s wings. Wyverns have five fingers on their forelimbs. The first three fingers are claws that can slash at prey while on the ground. The last two fingers are stretched out to support an extendible membrane where the feathers are set. The average wingspan is longer than a wyvern’s overall length from snout to tail tip.
The length of the tail in proportion to the rest of the body changes depending on the breed. Most wyvern breeds have a tail that is two thirds the overall length of the body. Other breeds have a tail that is half of the overall length. Longer tails are preferred in combat wyverns and help to steer and maneuver with more precision. Longer tails with barbs are also a more effective offensive weapon. Shorter tails are preferred because they reduce drag in flight and extend a wyvern’s flight range. Tails can have barbs or spikes down the last third of the length and spades on the tips. Barbs and spikes are present to conduct electricity and give foes a nasty electric sting. Wyverns with spades on their tails are better and maneuvering through the air and can make sharper turns. Long feathers extend from the first half of the tail’s length and produce more lift in the air.
The legs of a wyvern account for about two thirds of the height. They are well adapted for running. Wyverns have a digitigrade stance and their heels are kept off of the ground. There are four toes on the legs. The first toe points backward. The next three toes point forward with the middle toe being the longest. The legs are feathered above the heel and scaled below.
The majority of the torso is feathered. The back is armored with scales fused into overlapping ridges that look not unlike the tail of a lobster. These ridges run along the length of the entire spinal column. The scales are very dense and can withstand a pistol bullet. The sternum is keeled like a bird’s to support the large breast muscles necessary for such strong wing strokes.
Wyvern bones are pneumatized to reduce weight. The hollow in the bones are filled with air and methane to further reduce weight.
Wyverns are surprisingly adapted for flight despite their large size. The sternum is keeled like a bird’s to support large chest muscles to produce strong flapping strokes in the wings. The muscles in the wrist are stronger than a bird’s to create an powerful flap. The fourth and fifth digits on the hand are elongated to support a membrane from whence the primary feathers are attached. These fingers can be lifted and lowered independently to angle the wing tips. This helps to turn in the air. The fourth and fifth digits can also be brought together and fanned apart to alter the wing’s surface area. They are brought together to minimize air resistance during upbeat and they are spread out to increase surface area during downbeat.
A wyvern’s tail also aids in flight. Some breeds have a wide bony spade on the tip of tail that helps to steer. The first third of the tail near the pelvis supports large feathers that spread out in flight and increase surface area to help soar for longer periods.
The lungs of a wyvern work on the same principal as other theropod lungs. They have no diaphragm and rely on a series of air sacs that acts as bellows and move the air in and out of the lungs. Unique bacteria in the digestive system produce gas as a byproduct of their respiration. Specialized blood cells move the gas from the intestines to the lungs where they are drawn into the gas sacs. The gas is spread into the hollows of the bones and other gas sacs. The gas sacs greatly help to reduce the wyvern’s overall weight.
The most notable and feared of a wyvern’s abilities is fire-spitting. Wyverns are able to spit flaming saliva at targets up to fifty meters away through a complex biologic process. Gas produced in the aforementioned gas sacs is exhaled through the nostrils at high pressure. The horns on the wyvern’s head conduct electricity produce in electrocytes throughout a wyvern’s body. They produce enough electricity to create an electric arc in between them. The arc is timed so that it ignites methane just as the gas is exhaled to ignite it.
A dewlap hangs underneath a wyvern’s throat. The dewlap is brightly colored in males for display purposes. The dewlap in both sexes also contains glands that produce a flammable liquid. This liquid is channeled through glands into the mouth. A wyvern’s tongue is long and the edges can curve upward to create a U-shape. The tongue acts as a channel for the saliva. Heavy iron deposits in the upper and lower jaws can channel enough electricity from the electrocytes to create a significant magnetic field. This field has an effect on the saline saliva and helps to propel it through the mouth like a magnetic gun.
An adult wyvern can time the exhaled gas, electric arc, and spat saliva with such precision that the flame ignites the saliva when it leaves the mouth. This is how wyverns are able to spit fire.
Some wyvern breeds, such as the Surgers, are unable to create a sufficient electric arc in between their horns and are unable to ignite their saliva. Many breeders envenom Surger saliva with bacteria colonies injected into the dewlap. The saliva is projected with such force that it can pierce skin.