Researchers from the Sleep Team at the Lyon Neuroscience Research Center (CNRS/INSERM/Claude Bernard Lyon 1 University/Université Jean Monnet), together with a colleague from the MECADEV research laboratory (CNRS/Muséum National d'Histoire Naturelle) have confirmed that lizards exhibit two sleep states, just like humans, other mammals and birds. They corroborated the conclusions of a 2016 study on the bearded dragon (Pogona vitticeps) and conducted the same sleep investigation on another lizard, the Argentine tegu (Salvator merianae). Their findings, published in PLOS Biology, nevertheless point out differences between species, which raises new questions about the origin of sleep states.