Fossil hunters tell a short story
Dinosaur with a stubby neck bucks the Diplodocus trend.
Competing for food in the wild can be a pain in the neck, so a dinosaur known as Brachytrachelopan mesai evolved a shorter one.
A fossil has recently been discovered of this short-necked dinosaur that lived in Patagonia, Argentina, about 150 million years ago, during the Late Jurassic period. It is a member of the sauropod group of dinosaurs, which includes the 30-metre-long giant Diplodocus.
Sauropods typically had long necks, which is thought to have allowed them to reach high into trees to maximize their food intake. But the fossil of B. mesai shows that it measured less than 10 metres, even after reaching adulthood
A long neck is an unnecessary and energetically expensive asset for a creature if food is readily available on the ground, and this could explain the existence of B. mesai, says Oliver Rauhut of the Bavarian State Collection for Palaeontology and Geology in Munich, Germany. "Nature tends to eliminate structures that are not needed for that reason," he explains. He and his colleagues report their find in this week's Nature1.
"It was a really well-preserved specimen," Rauhut adds, "although we found it a few thousand years too late after erosion had already begun to have an impact."
Paul Barrett, a palaeontologist at the Natural History Museum in London, points out that Patagonia lacked bird-footed dinosaurs called ornithopods, which grazed the Jurassic plains of other continents. This means that B. mesai might have faced little competition for resources.
This particular fossil also provides exciting clues about the evolution of sauropods, the team says. The short-necked dinosaur's closest relative comes from Africa. Brachytrachelopan mesai bears less similarity to more recently evolved sauropods in South America, and even weaker resemblance to those in Northern continents.
All of this hints that it evolved swiftly in the middle Jurassic period, after the separation of continents of the Southern and Northern Hemispheres but before Africa and South America fully broke apart. "It looks like this is a dinosaur that's trying to reinvent itself," says Barrett. "This fossil is telling us a lot about how these ecosystems evolved."
- Rauhut O. W. M., et al. Nature, 435. 670 - 672 (2005).
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