In Dragonsdawn, the race was intentionally engineered to fight Thread, a deadly mycorrhizoid[check spelling] spore that devours all organic matter that it touches, after it first caught the human colonists on Pern unawares with devastating results.
Geneticist Kitti Ping Yung designed the dragons by manipulating the genetic code of the indigenous fire-lizards that had been acquired as pets by the colonists.
Later genetic manipulation by Ping's granddaughter, Wind Blossom, also resulted in the watch-whers, ungainly, nocturnal creatures who bore a slight resemblance to dragons.
Periods between Passes, when the Red Star's orbit takes it away from Pern, are referred to as "Intervals"; usually lasting about two hundred Turns.
Unlike the dragons of Terran legend, they have a smooth hide rather than scales; the texture of their skin is described as being reminiscent of suede with a spicy, sweet scent when clean.
Kitti Ping designed the dragons to gradually increase in size with every generation until they reached pre-programmed final dimensions.
Ramoth's great size is often attributed to mutation and the genetic isolation of Benden Weyr for over 400 years (or Turns).
Because young dragons grow so fast, their riders must regularly apply oil to their hides to prevent the skin from cracking or drying out.
Dragons, like their fire-lizard ancestors, can breathe fire by chewing a phosphine-bearing rock, called "firestone" in the novels, which reacts with an acid in a special "second stomach" organ.
They also imprint on the first individual who feeds them after they hatch, creating a telepathic bond with them; the Pernese call this phenomenon "Impression".
In creating dragons, Kitti Ping intensified the creatures' telepathy, greatly increased their intelligence, and gave them a strong instinctive drive to Impress to a human.
Upon hatching, each dragonet chooses one of the humans present (usually) and Impresses to that person; from that moment on, the pair are in a constant state of telepathic contact for as long as they both live.
If a dragon attempts to teleport without a clear mental image of the place where they intend to reappear, they may simply fail to emerge from between and thus, be gone forever.
This idea originated with a statement by Anne McCaffrey herself, in answer to a fan's question about the subject at a con.
The Skies of Pern references the use of dragon dung as a repellent against the large felines inhabiting the southern continent.
As a safeguard against the possible damage that could be caused by such powerful creatures, Ping engineered dragons to be profoundly psychologically dependent on their riders.
On canon Pern, barring rare mutations, female dragons and fire-lizards are always either green or gold in color, while males are blue, brown or bronze.
Perhaps as a result of this, it is commonly believed that the larger colors are more intelligent, although recent novels imply that this may not be true.
The Pernese believe that chewing firestone makes female dragons sterile; they therefore refuse to allow queens to use it.
However, Dragonsdawn suggests that Kitti Ping—possibly motivated by old-fashioned ideas about gender roles—deliberately engineered greens to be infertile and gold dragons to be incapable of producing flame in order to protect the gold dragons, the only reproductively fertile females, from the dangers of Thread fighting.
For this reason, queen riders are strongly encouraged to restrain their dragons from eating heavily just before a flight, instructing them to drink blood instead for a quick burst of energy.
Due to the intense psychic bond between rider and dragon, dragonriders are overcome by the powerful emotions and sensations associated with mating flights.
Mirrim, known to be an extremely acerbic and temperamental rider, shows no jealousy or other problem with her weyrmate's regular sexual contact with Talina.
This is especially common among young teens working out in the fields who react to the sudden, unexpected and overwhelming urges with potentially embarrassing results.
Anne McCaffrey has stated in a number of documents and interviews that dragonets use pheromones to determine the sexual orientation of the humans to whom they Impress.
Many members of online Pern fandom find McCaffrey's ideas about sexuality highly questionable for a number of reasons, both scientific and ethical.
(Most infamously, she claimed in an interview that science has proven that being the receptive partner in anal sex triggers a hormonal change that will make a previously heterosexual man become homosexual and effeminate.
For the purposes of roleplaying games, McCaffrey has also officially allowed females (masculine lesbians) to ride browns or blues, though she insists that this could never happen on her (canon) Pern.
However, this concept is not seen in other books and clearly does not exist in the Ninth Pass, as several problems arise regarding green and gold riders who object to the random nature of mating flights and end up raped by the male winner of the flight (most notably in Skies of Pern).
As the primary line of defense against the Thread, dragons are a requirement for the survival and prosperity of humans and other land life on Pern.