Artistic License - Paleontology: It seems the creators were so preoccupied with making their dragons authentic that they didn't bother to check if their other prehistoric creatures were accurate. The T-Rex has pronated hands that are slightly too long, the pterosaurs are of the standard Ptero Soarer variety (not to mention that they are clearly supposed to be Pteranodons, despite living inland and being shown as scavengers), and the humans in the Forest Dragon segment clearly have European features, despite this segment taking place in prehistoric China.
There's a bit of Anachronism Stew thrown in as well; Pteranodon was featured at the time of the K-Pg event despite having already gone extinct twenty million years prior, and they have pot-bellied pigs existing almost forty thousand years before there were any kind of domestic pigs at all.
Atlantis Is Boring: The Marine Dragon segment of the documentary is much shorter than those of the 3 terrestrial dragons (Prehistoric, Forest, and Mountain). It was mostly shown to explain how dragons survived the KT event that killed the dinosaurs.
Dinosaurs Are Dragons: Subverted. Despite first popping up right alongside the dinos, dragons are stated to be highly derived crocodilians.
Dragon Hoard: Dragons are naturally attracted to shiny objects, and may collect hoards of such items, more or less valuable, to allure potential mates.
The Ghost: The dragon family tree reveals a "Desert Dragon" on the name list. We never find out what it is, looks like or anything about it. The only thing we can guess about it is that it lives in a desert.
Mama Dragon: The prehistoric dragon mother. Same goes for the mountain dragon, who did her very best to protect and provide for her daughter.
Meanwhile, in the Future: The show alternates between depicting the lives of the various dragon species in the past, and showing Dr. Tanner and his team in the present-day searching for evidence and speculating about the biology of these animals.
Sea Monster: The Sea Dragon is used to explain legends about sea serpents and other aquatic monsters.
Shoot the Shaggy Dog: The story of the Prehistoric Dragon seems to be this. The young dragon lost his mother to a T-Rex. He barely avoids death at the hands of an older dragon. Later he grew up and then he managed to defeat another dragon. With that he managed to gain his own territory and his own mate. But then theK-T Extinction Eventhappens.
Possibly a subversion, since it is never stated exactly how long before the K.T. event the young dragon lived, so the segment could just as easily have fast-forward a few hundred thousand years after the events of the dragon's life to show the infamous extinction event.
Shown Their Work: The premise of the documentary is to show how giant six-legged, flying lizards that breathe fire could exist. And it mostly succeeds.
Stock Footage: You'll be seeing that shot of the mountain dragon's head entering the frame, then turning to face something a lot. Sometimes it's flipped so she's looking the other way. Along with several other shots recycled several times (curiously, only the mountain dragon segment has this reuse of footage).
Together in Death: In the end, the mother dragon and the daughter dragon that was discovered and studied was put in a museum exhibit together.
Too Dumb to Live: The human hunters in the mountain dragon segment, one of whom thought it was a good idea to charge straight into the path of a rhinoceros-sized flying predator that breathes fire and presumably killed tens of other hunters who made the same mistake.
Vertebrate with Extra Limbs: Most species shown have six (four legs and two wings). The "Marine Dragon" they presumably descend from has four (two wings and two legs) and the extra legs came to be via a later, somewhat massive mutation that affected the homeobox genes that regulate growth and development in animals.
The Worf Effect: Look, a Tyrannosaurus rex! What do you think will be the dragon's breakfast? Subverted: the Tyrannosaurus almost killed the young dragon, the mother only wanted it gone, and used her fire only after the T. rex had grabbed and broken her wing, dooming her as well. So the fight was pretty much a draw.
The also prehistoric, but much more recent, Chinese Dragon preys on tigers.