Beaded Lizard - Taxonomy

Taxonomy

The beaded lizard has one close living relative, the Gila monster (H. suspectum), as well as many extinct relatives in the Helodermatidae whose evolutionary history may be traced 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 indicates that the beaded lizard is better placed in a separate family.

The species was first described in 1829 by Arend Wiegmann as Trachyderma horridum, however, he renamed it Heloderma horridum six months later. Its 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.

There are four subspecies of beaded lizard:

• Mexican beaded lizard (Heloderma horridum horridum) (Wiegmann, 1829)
• Black beaded lizard (H. h. alvarezi) Bogert and Martin del Campo, 1956
• Rio Fuerte beaded lizard (H. h. xasperatum) Bogert and Martin del Campo, 1956
• Motagua Valley beaded lizard (Heloderma horridum charlesbogerti) Campbell and Vannini, 1988