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Kangaroo finding is a leap forward

16 July 2001: ASSUMPTIONS about ancestral links between animal species based on genetic mapping may be completely wrong, say scientists who have discovered that the kangaroo is not related to the duck-billed platypus.

The findings support the traditional approach of linking animals by anatomical traits.

Analysis of mitochondrial DNA, which is inherited through the maternal line, is now the main method of classifying how mammals evolved.But it has led scientists to believe that some animals with very different anatomies are related — for instance, the kangaroo and the platypus, and the hippopotamus and whale.

Scientists at Duke University in North Carolina put the idea to the test by analysing DNA sequences in a nuclear gene taken from 15 different mammals. The results clearly showed that the kangaroo and platypus came from different evolutionary backgrounds.

The findings appeared to support the theria hypothesis of classifying groups of mammals. This holds that eutherians (including humans, rats, pigs and whales) and marsupials (kangaroos, wallabies, koalas) evolved from a common ancestor, and monotremes (platypus, echidna) evolved from a different ancestor on a separate land mass.

Mitochondrial analysis supports the rival marsupionta hypothesis, which places the platypus and kangaroo together.