A 375 million-year old fossilised umbilical cord indicates that placoderm, thought to be ancestors of modern fish, are actually closer to sharks and rays.  This requires changes to current theories of the evolution of vertebrate sexual reproduction. 
The placoderm, a class of prehistoric fish known as the "dinosaur of the seas", dates back to the Devonian period, making the fossil the earliest known case of a vertebrate that gave birth to live young. It is also the only fossilised umbilical cord ever to be found.
Dr. John Long, Museum Victoria's head of sciences and the leader of the team examining the fossils, says the find "changes our understanding of the evolution of vertebrates".
He and Dr. Kate Trinajstic from the University of Western Australia were writing a paper on the fossil that was found during an Australian Research Council-funded expedition to the Gogo Formation, near the town of Fitzroy Crossing in Western Australia. They decided to give the fossil one last inspection, at which point they discovered the embryo. According to the research team, this discovery pushes the known development of viviparity (animals giving birth to live young) back 200 million years, and also marks the earliest known development of internal fertilisation, a feature now found in sharks and rays.
Dr. Long gave the species the Latin name Materpiscis attenboroughi. Materpiscis derives from the Latin words meaning "mother fish", and attenboroughi was chosen in honour of Sir David Attenborough, who first drew attention to the Gogo region's possible fossils in a 1970s TV documentary.
The team's findings were published in the science journal Nature, and the fossil specimen will be on display at the Melbourne Museum.

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First fertilised fish fossil found