SYDNEY, April 24 -- Giant prehistoric kangaroos perished when "climate upheaval" turned lush Australian rainforest into desert, scientists said yesterday after studying ancient fossils with new techniques.

Weighing as much as 170 kilogrammes (375 pounds) - almost twice as hefty as the chunkiest living kangaroos - the extinct "Protemnodon" bounded across Australia as many as five million years ago.

Researchers were able to recreate the foraging habits of one population by matching long-lived chemicals from fossilised teeth to recently unearthed rocks.

Similarities in chemical composition helped to mark how far the kangaroos hopped in search of food.

"Imagine ancient GPS trackers," said Queensland Museum scientist Scott Hocknull.

"We c...