Furthermore, the researchers contend that over time these species have switched back and forth in their preferred reproductive mode.
Alex Pyron, Robert F. Griggs Assistant Professor of Biology at the George Washington University, said that the finding is very unusual and controversial, and a major overturn of an accepted school of thought.
Before, researchers long assumed that the ancestor of snakes and lizards laid eggs, and that if a species switched to live birth, it never reverted back, researchers said.
The findings push researchers' understanding of the evolution of live birth a lot further back in time to 175 million years ago, showing that live birth has a much more ancient past as a strategy than previously believed.
The findings are backed by several recent plesiosaur and mosasaur fossil discoveries and the fossil record of a few lizards from the Cretaceous Period, which had embryos in the mother and had live birth.
Pyron had previously analyzed an evolutionary tree containing all groups of squamates, the group that comprises lizards and snakes.
The tree, which uses DNA sequencing technology to group thousands of lizards and snakes, includes all families and subfamilies and most genus and species groups.
In total, about 115 groups of lizards and snakes, or about 2,000 species, have live birth. The other 8,000 species lay eggs-at least right now.
The study is published in the journal Ecology Letters.
--ANI (Posted on 18-12-2013)