September 21, 2009

Evolution of extinct sea creatures studied

U.S. and British scientists say they've determined the transition of extinct sea creatures from egg-laying to live-born opened up evolutionary pathways.

Scientists at Harvard University and the University of Reading say they also determined the evolution of such live-born young depended crucially on the advent of genes -- rather than incubation temperature -- as the primary determinant of offspring sex.

In the study of three lineages of extinct marine reptiles -- mosasaurs, sauropterygians and ichthyosaurs -- the scientists said genetic sex determination might have played a strong role in the colonization of the world's oceans by a diverse array of species.

Determining sex with genetic mechanisms allowed marine reptiles to give live birth, in the water, as opposed to laying eggs on a nesting beach, Chris Organ, a Harvard research fellow, said. This freed these species from the need to move and nest on land. As a consequence extreme physical adaptations evolved in each group, such as the fluked tails, dorsal fins and the wing-like limbs of ichthyosaurs.

Co-researcher Daniel Janes added, Losing the requirement of dry land during the life cycle of ichthyosaurs and other marine reptiles freed them to lead a completely aquatic existence, a shift that seems advantageous in light of the diversification that followed.

The study that included Andrew Meade and Mark Pagel of the University of Reading appears in the journal Nature.