The Helodermatidae or beaded lizards are a small family of lizards endemic to North America today, mainly found in the Isthmus of Tehuantepec in Oaxaca, the central lowlands of Chiapas, on the border of Guatemala, and in the Nentón River Valley, though they were formerly more widespread in the ancient past. Traditionally, the
Gila monster
The Gila monster (''Heloderma suspectum'', ) is a species of venomous lizard native to the Southwestern United States and the northwestern Mexico, Mexican state of Sonora. It is a heavy, slow-moving reptile, up to long, and it is the only ve ...
and the
Mexican beaded lizard were the only species recognized, although the latter has recently been split into several species.
While the fossil record of this family may date back to as far as the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
with genera such as ''
Primaderma'' and ''
Paraderma'' of North America, the oldest definitive members of the Helodermatidae date to the
Early Oligocene
The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
, with ''
Lowesaurus matthewi'' from North America (Nebraska) and ''
Eurheloderma gallicum'' from Europe (France).
References
{{Authority control
Lizard families
Taxa named by John Edward Gray