Biology 342 Fall 06 Trevor Young
The debate over where snakes belong
The phylogeny of snakes is uncertain at best. Here I present three different phylogenetic trees and how they are each important to the continuing debate snake evolution. The first phylogenetic tree is from the Tree of Life web project and depicts the generally accepted phylogenetic tree. The second is from a recently published article that groups all the venomous reptiles into a venom clade based on new cDNA research. The final phylogenetic tree is from another recently published article about the ancestral snake Najash rionegrina.
(Snakes are the suborder Serprentes of Squamata)
A recent letter to Nature from Fry et al. (2006) showed the presence of venom toxins in two lizard families that were unknown to have secreted toxins at all, Iguania and Varanidae . The researchers conducted this research by taking cDNA toxin libraries from the known poisonous lizards and snakes and looking for homology with members of Iguania and Varanidae. The homology between the toxin libraries suggests the evolution of toxin producing glands before the separation of these families. The resulting rearrangement of the phylogenetic tree also causes the researchers to hypothesize a single evolution of venom production occurring about 200 million years ago. The researchers theorize this common ancestor would have had both mandibular and maxillary toxin secreting glands, of which the maxillary glands were retained in snakes, the mandibular glands were retained in anguimorphs (gila monsters), and both were retained in the iguanian lizards.
The Gila monster (left, courtesy of gila-monster.org) and the Lace monitor (right, courtesy of Wikimedia Commons) to members of the venom clade along with snakes.
This is an interesting deconstruction of a letter to Nature about the Najash rionegrina, a recently discovered fossil considered "the most basal snake, lying outside the clade consisting of all living snakes" (Actual Nature letter) .
1. Fry, B.G. et al. Early evolution of the venom system in lizards and snakes. Nature 439, 584-588 (2006).
2. Apesteguía, S., & Zaher, H. A cretaceous terrestrial snake with robust hindlimbs and a sacrum. Nature 440, 1037-1040 (2006).