Armavipers are generally described as a cross between Terran armadillos and vipers. This could be hard to understand, considering armadillos are mammals and vipers are reptiles. It must be said that armavipers are themselves reptiles, with much more in common with vipers than armadillos. The one thing they actually have in common with armadillos is that rather than typical snake scales, armavipers are covered in scutes, which gives them greater protection than most snakes have. (These scutes are the reason their DNA was one of the ingredients that would eventually be used in the creation of Dragons.)
Armavipers were first discovered living in the area were Tonad was settled, in LY 225, though in the years since then they have also been found to live in various other areas of First Land and Near Land. They were given their name by a spirit-talker and biologist named Javier, based on a recommendation from a spirit, who was the first to mention their resemblance to armadillos and vipers (naturally enough, since no one but a spirit would be likely to know of such things).