Gila Monster - Taxonomy and Etymology

Taxonomy and Etymology

There are two subspecies of Gila monster: the reticulate Gila monster (H. s. suspectum) and the banded Gila monster (H. s. cinctum). The reticulate Gila monster lives in the southern region of the Gila monster's range, while the banded Gila monster is a northern subspecies occurring primarily in the Mojave Desert. The reticulate Gila monster tends to have its lighter markings broken up by dark scales, giving it a reticulated pattern, while the banded Gila monster generally has more unbroken bands of lighter scales.

The Gila monster has one close living relative, the beaded lizard (H. horridum), 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 lived, and fragments of osteoderms from the Gila monster have been found in late Pleistocene (8000–10,000 years ago) deposits near Las Vegas, Nevada. Because the Helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils. Although the Gila monster 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 Gila monster is better placed in a separate family.

The name Gila refers to the Gila River Basin in Arizona, where the Gila monster was once plentiful. Heloderma means "studded skin", from the Ancient Greek words Helos (ηλος), "the head of a nail or stud", and derma (δερμα), "skin". Suspectum comes from the describer, paleontologist Edward Drinker Cope, who suspected that the lizard might be venomous due to the grooves in the teeth.