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Evolution of extinct sea creatures studied

September 21, 2009

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.


Source: upi



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