In the shadow of Cerro Condor, a 600-metre-high limestone bluff in Patagonia, two young palaeontologists gaze over waves of mountain ridges running west towards the Andes. Diego Pol and Ignacio Escapa, from the Egidio Feruglio Palaeonto-logical Museum in Trelew, Argentina, have spent years trekking the winding gravel trails here in the Chubut River valley, meeting only wandering guanacos, rheas and sheep. Already, their team has hand-dug half a dozen quarries in nearby canyons that have yielded globally important fossils. But many prizes remain among the uncharted sediments of the Middle Jurassic, a geological epoch spanning 160 million to 180 million years ago, when dinosaurs, plants and early mammals were all undergoing key evolutionary changes. This time period holds crucial clues to the explosion of evolutionary diversity in both dinosaurs and mammals. The oldest known dinosaur remains, for instance, are around 230 million years old; the oldest known fossil mammals have been dated at 193 million years ago. Both groups diversified to an enormous extent during the Middle Jurassic, yet relatively few sediments of that age have been studied. That makes Chubut province in southern Argentina a rare opportunity. "This has the potential to be a global landmark for the Middle Jurassic," says Pol. "For the Southern Hemisphere, it already is."
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