Squamate placement source of squabble.

• Position: Reptilies

Squamate reptiles--lizards and snakes--are among the most diverse groups of vertebrates, with more than 9,000 living species. They are important for humans because venomous snakes cause thousands of deaths every year. At the same time, their toxins are a critical resource for many medicines, including those for heart disease and diabetes. Lizards and snakes also are important model systems for biological research, especially in ecology and evolutionary biology.

Studies of squamate biology, however, have been hampered by controversy over their evolutionary relationships, and some researchers consider their family tree to be unresolved. The problem is that studies based on traditional, anatomical characters and those based on molecular data from DNA sequences strongly have disagreed, especially on how the iguanas and their relatives (called iguanians) are related to snakes and other groups of lizards. Iguanians include horned lizards, flying dragons, and basilisks.

A study by scientists from the University of Arizona, Tucson, San Diego (Calif.) State University; the Smithsonian Institution, Washington, D.C.; Brigham Young University, Provo, Utah; and the University of Mississippi, Oxford, has helped to resolve this controversy, and it also offers new insights on the evolution of fossil lizards.

"Anatomical data puts iguanians at the base of the tree, whereas molecular data suggest that the iguanians evolved more recently and are closely related to snakes and a group including the monitor and alligator lizards, called the anguimorphs," indicates John J. Wiens, a professor in the UA Department of Ecology and Evolutionary Biology. 'The results of our study...