Reptilian ancestors hated laying eggs
Though most of snakelets and baby lizards are hatched out of eggs now, this was not the case about 175 million years ago when snakes and lizards preferred to give birth to their young, claims a new study.
"This is a very unusual and controversial finding, and a major overturn of an accepted school of thought," said Alex Pyron, Robert F. Griggs Assistant Professor of Biology in the Columbian College of Arts and Sciences at the George Washington University.
"Earlier, researchers long assumed that the ancestors of snakes and lizards laid eggs, and that if a species switched to live birth, it never reverted back. We found this wasn't the case," Pyron added.
Pyron analysed an evolutionary tree containing all groups of squamates - the group that comprises lizards and snakes. 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 now.
Pyron is now working to analyse all tetrapods - a group comprisisng animals with four legs, such as amphibians, reptiles, mammals and turtles - to see if there are any new surprises about the evolution of their reproductive modes.
He also wants to test the genetics at work behind the evolutionary switching of reproductive mode.
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.
The findings of the study have been published in the latest issue of Ecology Letters.
(Posted on 18-12-2013)