Nearly one fifth of all reptiles — turtles, snakes, lizards and crocodiles — are on a slippery slope toward extinction due to loss of habitat, overharvesting and other factors, a new report says.

The study is the first of its kind to summarize the global conservation status of reptiles. More than 1,500 species were selected at random from around the world for conservation assessments in an effort to gain a representative sample.