Most efficient thermoregulating lizard

The lizard most efficient at thermoregulation via the absorption of solar radiation is the lava iguana Liolaemus multiformis, a black-scaled species native to the Peruvian Andes. After spending just an hour basking in the sun in near-freezing external conditions of only 1.5°C, it can raise its body temperature to 33°C. Like all reptiles, this lizard species is poikilothermic or "cold-blooded", i.e., it cannot regulate its body temperature by metabolic (endothermic) means like mammals and birds can (and do), and is therefore totally reliant upon external heat sources to maintain its body temperature.