In studying Murray short-necked turtles in Australia, scientists from the University of Western Study in Western Australia find that the unborn babies send signals to encourage the speedier growth of their more slowly developing siblings so that no smaller turtles are left to hatch alone.

http://www.telegraph.co.uk/news/newstopics/howaboutthat/8925107/Turtles-communicate-with-each-other-before-hatching.html