February 4, 2009

Fossil Suggests Prehistoric Whales Gave Birth On Land

Scientists have uncovered two early whale fossils that may shed light on how these ancestors to modern whales evolved from walking on land to becoming sea dwellers.

Experts say the fetal remains found along with the 47.5 million-year-old pregnant female fossil were positioned head down, suggesting these creatures gave birth on land, while spending much of the rest of their time in the water.

Paleontologist Philip Gingerich, whose University of Michigan research team discovered the fossils in Pakistan in 2000 and 2004, said the tiny fetal teeth had him stumped at first.

"When I first saw the small teeth in the field, I thought we were dealing with a small adult whale, but then we continued to expose the specimen and found ribs that seemed too large to go with those teeth," he said.

"By the end of the day, we realized we had found a female whale with a fetus."

The discovery of the fetal skeleton is the first specimen of the extinct whale group known as Archaeoceti.

"This stunning discovery reinforces the belief that modern cetaceans originated from terrestrial ancestors," said H. Richard Lane, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.

The researchers say the find represents a new species named Maiacetus inuus, a hybrid of the words for "mother whale" and Inuus, the name of a Roman fertility god.

The female specimen revealed a fetus that was positioned head down like other land animals, allowing it to begin breathing right away.

Therefore, scientists suggest the group had not yet made the leap to giving birth in the water like modern whales, which are born tail first to allow them to start swimming right after birth.

The male specimen measured 8.5 ft and was found in the same fossil beds as the female. The male is about 12 percent bigger and had fangs that were 20 percent larger than those of the female.

Gingerich said the overly developed teeth suggest the creatures spent a large portion of their time catching and eating fish.

His said four flipper-like legs found on the fossils indicate the whales could have supported their weight on land, but only for short distances. Gingerich suggested it was likely the whales came on shore to mate, rest and give birth.

"They clearly were tied to shore," Gingerich said. "They were living at the land-sea interface and going back and forth."

The Maiacetus fossils appear to represent an intermediate whale form, showing the evolution from land dwelling to aquatic creatures, he wrote in the Public Library of Science journal PLoS ONE.

"Specimens this complete are virtual 'Rosetta stones'," Gingerich said, "providing insight into the life history of extinct animals that cannot be gained any other way."


Image Caption: Artist's conception of male Maiacetus inuus with transparent overlay of skeleton. Credit: John Klausmeyer and Bonnie Miljour, University of Michigan


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