May 29, 2008

Australian Scientists Discover Oldest Live Birth

Scientists in Australia reported Thursday they had discovered the remains of the oldest vertebrate mother ever found. The fossilized 375-million-year-old placoderm fish, preserved with an embryo still attached with an umbilical cord, was found in the Gogo area of northwest Australia.     

The fossil fish is the oldest-known example of a mother giving birth to live young, and pushes back the emergence of this reproductive technique by some 200 million years. Prior to the discovery, the earliest evidence for this form of reproduction came from reptile fossils dating 248 to 65 million years ago during the Mesozoic Era.

The scientists have named their 25-cm fossil Materpiscis attenboroughi, in honor of Sir David Attenborough, who first spotlighted the Gogo fish sites in the 1979 series Life on Earth.

The find offered proof that an ancient species had advanced reproductive biology comparable to modern sharks and rays, according to John Long, head of sciences at the Museum of Victoria in Melbourne.

"It is not only the first time ever that a fossil embryo has been found with an umbilical cord, but it is also the oldest known example of any creature giving birth to live young," Long said in an interview with Reuters.

Frequently referred to as "the dinosaurs of the seas", placoderms ruled the planet's seas and lakes for close to 70 million years during the late Devonian period, when land animals evolved from fish. And while most were quite small, some grew to over 20 feet in length. 

"This discovery changes our understanding of the evolution of vertebrates," Long said.

"It will make us rethink the early evolution of vertebrate in terms of how reproduction has driven evolutionary events."

Long said little was understood about how reproductive changes from spawning eggs to internal fertilization affected the evolution species.

"The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac," wrote the scientists in a report about the discovery.

"Our new example extends the definite record of vertebrate viviparity (giving birth to live young) back by some 200 million years," the scientists wrote, adding that the newly discovered fossil indicates internal fertilization and viviparity in vertebrates as originating earliest within placoderms.

"The existence of the embryo and umbilical cord within the specimen provides scientists with the first ever example of internal fertilization, sex, confirming that some placoderms had remarkably advanced reproductive biology," Long said.

"This is the first bit of evidence on how a complete extinct class of animals may have reproduced."

The fossil will go on display in the Melbourne Museum May 29. 

A report about the finding was published in the latest issue of the journal Nature. 


On the Net:

Museum Victoria

An abstract can be viewed at http://www.nature.com/nature/journal/v453/n7195/abs/nature06966.html.