Mexican beaded lizard generic name "Heloderma" means "studded skin", from the Ancient Greek words "hêlos" (ἧλος)—the head of a nail or stud—and "dérma" (δέρμα), meaning skin. Its specific name, "horrĭdum", is the Latin word meaning rough or rude. The four subspecies of beaded lizard, elevated to full species in 2013, are: Adult beaded lizards range from in length. They are substantially larger than the Gila monster, which only reaches lengths of . The snout-to-vent length of a beaded lizard averages . The average body mass of an adult beaded lizard is , about 45% heavier than the average mass of a gila monster,
Mexican beaded lizard back to the Cretaceous period. The genus "Heloderma" has existed since the Miocene, when "H. texana" ranged over most of North America. Because the helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils. Although the beaded lizard appears closely related to the monitor lizards (varanids) of Africa, Asia, and Australia, the wide geographical separation and unique features not found in the varanids indicate the beaded lizard is better placed in a separate family. The species was first described in 1829 by Arend Wiegmann as "Trachyderma horridum", but he renamed it "Heloderma horridum" six months later. Its