Toxicofera



Toxicofera (Latin for "those who bear toxins"), is a clade which represents about 4600 species (nearly 60%) of Squamates; it encompasses all venomous reptile species, as well as numerous related non-venomous species.

Details
Toxicofera combines the following groups from traditional classification:


 * suborder Serpentes (snakes)
 * suborder Iguania (anoles, chameleons, iguanas, etc.)
 * infraorder Anguimorpha, consisting of:
 * family Varanidae (monitor lizards, including the Komodo dragon)
 * family Anguidae (alligator lizards, glass lizards, etc.)
 * family Helodermatidae (Gila monster and Mexican beaded lizard)

Background
Until recently, venom in Squamates was only known in Serpentes and Helodermatidae. Venom and venom genes have since been documented in species from groups (Iguania and Varanidae). In 2003 the Toxicofera hypothesis was proposed, after work by Fry et al showed that nearly all "non-poisonous" snakes produce venom to a certain extent. This suggested a far more ancient origin for venom in Serpentes than had been considered until then. The formal name Toxicofera was given in 2005 replacing the unofficial "venom clade" naming. Comptes Rendus Biologies

Conclusions
It was estimated that the common ancestral species that first developed venom in the venom clade lived on the order of 200 million years ago, approximately 100 million years before snakes evolved.

The venoms are thought to have resulted after genes normally active in various parts of the body duplicated and the copies found new use in the salivary glands.

The newly discovered diversity of Squamate species producing venoms is a treasure trove for those seeking to develop new pharmaceutical drugs; many of these venoms lower blood pressure, for example.

Papers

 * Molecular Evolution and Phylogeny of Elapid Snake Venom Three-Finger Toxins July 2003
 * The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes Available online October 27, 2005
 * Early evolution of the venom system in lizards and snakes Available online November 16, 2005