Phylogenetic relationships among major groups of snakes

(Illustration by Argosy. Courtesy of Gale.)

Alethinophidia

Alethinophidia

Alethinophidia

Macrostomata

Caenophidia

Colubroidea

Macrostomata

Caenophidia

Colubroidea

(Illustration by Argosy. Courtesy of Gale.)

Anomalepididae

Leptotyphlopidae

Typhlopidae

Anomochilus

Anilius scytale

Cylindrophis

Uropeltidae

Loxocemus bicolor

Xenopeltis

Boidae

Pythonidae

Bolyeriidae

Tropidophiidae

Acrochordidae

Viperidae

Atractaspididae

Colubridae

Elapidae

When the northern Laurasian plate separated from the southern Gondwanan plate in the mid-Jurassic, two isolated landmasses were formed. Gondwana presumably held primitive iguanians and gekkotans, whereas Laurasia must have contained ancestral eublepharid geckos, scincomorphans, and anguimorphans. When Gondwana broke apart, its iguanians and gekkotans became isolated on the three large southern landmasses, Africa (agamids, chameleons, and gekkonids), South America (iguanids and sphaerodactyline geckos), and the Australian region (agamids and diplodactylid geckos).

Gekkonids and skinks dispersed widely and became virtually cosmopolitan. Both crossed oceans by rafting and moving across land bridges. Other groups either remained confined to the landmass of origin (cordylids, corytophanines, crotaphytines, diplodactylids, gymnophthalmids, heloder-matids, hoplocercines, lanthanotids, leiocephalines, leiosaur-ines, liolaemines, oplurines, phrynosomatines, pygopodids, sphaerodactylines, tropidurines, and xantusiids) or exhibited a more limited dispersal (agamids, anguids, chamaeleonids, iguanids, lacertids, teiids, and varanids). Exactly when and how snakes diversified and colonized the continents remains poorly understood, but within snakes, scleroglossan evolution produced groups as diverse as fossorial (adapted to digging) burrowers that live in social-insect colonies (scolecophidians) and sea snakes that inhabit the world's warm oceans (Hy-

maxilla

Mosquito Enteric Nervous

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