Pliny the Elder [1st century CE] (Natural History, Book 9, 43): The sea-snake [draco marinus] when caught and placed on the sand, with marvelous rapidity digs itself a hole with its beak. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:42): The sea-dragon [draco marinus] has stingers in its arms, oriented toward the tail. When it strikes, it emits poison into whatever spot it attacks. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.15): The sea-dragon is a monster of horrible cruelty. It is as long as a terrestrial dragon, but lacks wings. It has a coiled tail, a small head in proportion to the size of its body, but a large gaping mouth. It has scales and a hard skin. It is a pestilence to fish and other sea creatures, for any fish or an animal that it bites dies. Even a man will not escape if he is wounded. It has fins for wings, which it uses in swimming. It crosses great spaces of the sea at one stroke, and this rather by the force of his strength than by the oars of its fins. If a sea-dragon, as Pliny says, is captured and cast into the sand, it digs a cave for itself with wonderful agility with its beak. The ashes of its bones heal toothaches. - [Badke translation/paraphrase]

Albertus Magnus [ca. 1200-1280 CE] (De animalibus, Book 25, 12): Haren, according to the philosopher Semerion, is a serpent which belongs to the genus of marine dragons, an opinion also shared by Avicenna. It is similar to the serpent or dragon called carnen, also one of the sea dragons, and is large enough to attain a length of six cubits or more. It is dark in color and somewhat hairy near the head. When it bites, it leaves a large ugly wound, whose after-effects are not unlike those of a viper's bite. - [Scanlan]