Head-warming behavior of a regal horned lizard buried in sandy gravel. Phrynosoma solare. This lizard sleeps buried in sand; and in the morning, it emerges slowly and cautiously, exposing its head to the sun. By warming the head first, it can become fully alert while remaining otherwise hidden from predators. Sonoran Desert, Tucson Mountains, Tucson, Arizona, USA. Photographed under controlled conditions