- Dinosaurs were not just killed off when the asteroid
hit, they were struck down in their prime, suggests a new analysis of dinosaur
fossils around the world.
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- "Dinosaurs were just doing incredibly well at the
end of the Cretaceous," says David Fastovsky, a palaeontologist at
the University of Rhode Island at Kingston.
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- The first dinosaurs evolved about 230 million years ago
in the Triassic period. Early dinosaurs were generalists, and had evolved
into no more than around 40 genera at any one time up until the late Jurassic,
which began about 160 million years ago.
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- But then diversity soared in the Cretaceous which followed
(see graphic). Fastovskyís team has established that at least 245
dinosaur genera lived during the late Cretaceous period, from 99 to 65
million years ago.
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- Elaborate jaw
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- "The lifestyles of dinosaurs became much more diverse,"
says Fastovskyís colleague Peter Sheehan of the Milwaukee Public
Museum.
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- "By the late Cretaceous, we have much more specialised
animals." The diversity of plant-eating dinosaurs in the period is
"absolutely breathtaking", he told New Scientist.
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- For example, hadrosaurs evolved an elaborate duck-billed
jaw filled with teeth to chew vegetation, and the rhinoceros-like ceratopsians
evolved elaborate horns.
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- Earlier studies had suggested dinosaur diversity dropped
shortly before the asteroid impact, based on a drop in the number of genera
uncovered from the two final stages of the Cretaceous, the Campanian and
the Maastrichtian.
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- The new data also shows a slight decline between those
two stages, but statistically this difference is meaningless because very
few dinosaurs are known from other stages of the late Cretaceous.
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- - Journal reference: Geology (vol 32, p 877)
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