for National Geographic News
One size didn't fit all for the early dinosaur Plateosaurus, a new study suggests.
Fossils show the giant plant-eaters experienced sudden growth spurts, with some adults dwarfing others.
The study team estimates that the biggest individuals measured 33 feet (10 meters) in length and weighed almost 4 tons. Other dinos of the species were twice as small, managing an adult body length of only 15 feet (4.8 meters).
Researchers say the animal, which lived some 200 million years ago, had growth patterns like those seen in living reptiles but unlike those of other, later dinosaurs.
Scientists at the University of Bonn in Germany analyzed growth rings found in the fossilized leg and pelvic bones of Plateosaurus, a long-necked, two-legged dino once common across Europe.
The study, which appears tomorrow in the journal Science, suggests that adults grew at different rates and that their growth occurred either in rapid spurts or slow stretches depending on environmental conditions.
The scientists add that this growth model in such a large dino species means that Plateosaurus possibly marks an initial step in the evolution of genuinely warm-blooded dinosaurs.
Mammals grow "in accordance with a genetically programmed blueprint," said Martin Sander, a University of Bonn palaeontologist and lead study author.
Humans, for example, can reach different sizes as adults, but individuals' growth rates will be fairly predictable over time.
Dinosaurs were thought to have had steady growth patterns similar to mammals, but "our findings have thrown this conception into disarray, at least for one dinosaur," Sander said.
Sander and his colleagues say Plateosaurus probably had a similar metabolism to living reptiles. Like today's lizards, crocodiles, and turtles, the dinosaur's growth "was affected by environmental factors such as climate and food availability," the researchers report.
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