Heloderma
| Heloderma Temporal range: | |
|---|---|
 | |
| Gila monster, Heloderma suspectum | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Anguimorpha |
| Infraorder: | Neoanguimorpha |
| Clade: | Monstersauria |
| Family: | Helodermatidae |
| Genus: | Heloderma Wiegmann, 1829 |
| Type species | |
| Heloderma horridum Wiegmann, 1829 | |
| Species | |
Heloderma is a genus of toxicoferan lizards that contains five species, all of which are venomous.[1] It is the only extant genus of the family Helodermatidae.
Description
[edit]Species in Heloderma are stout-bodied lizards with bead-like osteoderms distributed in a non-overlapping pattern on most of their body.[2][3] Osteoderms are absent from their ventral scales. Heloderma lizards have wide heads with powerful jaws and fixed, immobile eyes.[4][5] Their tails are used as fat-storage organs. Most species are dark in color, with yellowish or pinkish markings.[6][7]
Venom
[edit]The venom glands of Heloderma are located at the end of the lower jaws, unlike snakes' venom glands, which are located behind the eyes. Also, unlike snakes, the Gila monster and beaded lizards lack the musculature to inject venom immediately by high pressure mechanism. They have to chew the venom into the flesh of a victim. Heloderma venom is used only in defense. Venom glands are believed to have evolved early in the lineage leading to the modern helodermatids, as their presence is indicated even in the 65-million-year-old fossil genus Paraderma.[7][8] In general, adult helodermatids have 15 to 20 mg of venom, while the lethal dose for humans is 5 to 8 mg of dried venom.[9]
Venom production among lizards was long thought to be unique to this genus, but researchers have identified several other lizards that produce some venom, all placed in the clade