Marsupial Family Tree Gets New Root; New Genetic Analysis Traces Group's Origins to South America

Article excerpt

The kangaroo's twisted marsupial family tree is now in order, thanks to jumping genes. Genetic evidence shows that a South American ancestor gave rise to all Australian marsupials, and that the South American opossums were the earliest group to branch off from the other six marsupial clans.

Distinctive for raising their live-born young in protective pouches, marsupials all trace back to a common ancestor that split from other mammals about 130 million years ago. But fossil and genetic evidence conflict about which subsequent marsupial species evolved first, and where.

Jumping genes provide new clues for solving the puzzle. These strands of DNA make copies of themselves to reinsert randomly in the genome--the entire set of genes in a cell's nucleus. Gene-jumping is rare, and each jump is unlikely to happen again. So if two species share a jumping gene, they probably inherited it from a common ancestor.

Maria Nilsson and colleagues at West-falische Wilhelms Universitat Munster in Germany compared jumping genes in the seven main branches of marsupials. …