Elephants may have started out all wet.
"For the first time, we now have a rational explanation for the unusual anatomical features of the elephant," says Ann P. Gaeth of the University of Melbourne in Parkville, Australia.
Some paleontologists, however, argue that this idea doesn't hold water.
The evidence comes from an investigation of seven fetal elephants found inside females that were shot to reduce overpopulation in a South African park. Gaeth and her colleagues studied the growth of kidneys and other organs in these specimens, the smallest of which had developed for only 58 days. Elephant gestation typically lasts 22 months.
The researchers were surprised to find dozens of small, funnel-shaped tubes, called nephrostomes, in the kidneys of the elephant fetuses. These features had not been seen in any mammal that gives birth to live young, the researchers report in the May 11 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. Nephrostomes appear briefly in the embryos of egg-laying mammals, such as the platypus, and function in adult fish and amphibians.
The elephant's fetal nephrostomes are a legacy that provides clues about the animal's origins, say the researchers. Aquatic animals have nephrostomes, so elephants may 'have inherited this feature from an aquatic ancestor, says Gaeth.
The same argument applies to the elephant's nose. The trunk appears early in fetal growth, suggesting that it has a more ancient origin than features popping up later during gestation, the Australian scientists say. The trunk may have evolved originally as a snorkel for early aquatic elephants, they speculate.
Other researchers don't discount the possibility that elephants arose from an aquatic mammal. Fossil bones, as well as genetic studies, suggest that elephants are closely related to manatees. Researchers have debated whether the ancestor of both groups lived on land or in the sea.
Paleontologists, however, argue that the fetal evidence doesn't provide much insight into elephant evolution. For instance, studies of the oldest elephant fossils indicate that these animals lacked trunks, an observation that contradicts the Australian researchers.
"I don't buy the argument about a trunk having first evolved in an aquatic environment," says Daryl P. Domning of Howard University in Washington, D.C., who studies fossil manatees.
"I'm not convinced by their arguments. I think they've overstated their case," agrees mammal paleontologist Andre Wyss of the University of California, Santa Barbara.
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|Article Type:||Brief Article|
|Date:||May 22, 1999|
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