[meteorite-list] Lucky Break Allowed Dinosarus To Rule Earth: Study

[Ron Baalke]

http://www.reuters.com/article/scienceNews/idUSN1128337120080911  

Lucky break allowed dinosaurs to rule Earth: study
By Will Dunham
Reuters
September 11, 2008

WASHINGTON (Reuters) - Thanks to a big stroke of luck 200 million years
ago, dinosaurs beat out a fearsome group of creatures competing for the
right to rule the Earth, scientists said on Thursday.

Dinosaurs appeared about 230 million years ago, during the Triassic
Period, and competed for 30 million years with a group of reptiles
called crurotarsans, cousins of today's crocodiles that grew to huge
sizes and looked a lot like dinosaurs.

Many scientists believed dinosaurs were simply superior to crurotarsans
and fared better because the earliest dinosaurs walked on two legs, not
four, and because they may have been warm-blooded.

But scientists led by Steve Brusatte of Columbia University and American
Museum of Natural History in New York conducted an extensive review of
fossils and found that the two groups were evolving at roughly the same
pace and the crurotarsans actually had a larger range of body types,
diets and lifestyles.

The dinosaurs won out, Brusatte concluded, because some type of
planetary calamity 200 million years ago -- dramatic climate change or
maybe a large meteorite impact -- nearly wiped out the crurotarsans
while sparing the dinosaurs.

"The fundamental question is why were the dinosaurs able to become so
dominant," Brusatte, whose study is in the journal Science, said in a
telephone interview. "Evolution on a big scale oftentimes is a matter of
luck."

The event that toppled the crurotarsans 200 million years ago enabled
dinosaurs to become the reigning form of land animals for a long time,
until their luck ran out too. An asteroid struck Earth 65 million years
ago and doomed the dinosaurs.

The crurotarsans were a fabulous bunch of monsters.  Some called 
phytosaurs looked and lived a lot like today's crocodiles, staying 
submerged in rivers or lakes until attacking a victim. The North 
American phytosaur Smilosuchus grew to 39 feet long.

Others called rauisuchians were land predators with four powerful 
legs, massive skulls and flesh-tearing teeth. South America's 
Fasolasuchus grew to 33 feet long.

Both were far more impressive than the typical dinosaur predator of 
the time like Coelophysis, a relatively lightly built, two-legged 
hunter about 10 feet long.

The dinosaur plant eaters of the time like Plateosaurus were getting 
big, but were less varied than the plant-eating crurotarsans such as 
the heavily armored aetosaurs.

"If we were standing around in the late Triassic period 210 million 
years ago and were asked what group is going to go on and take over 
the world, I think a reasonable gambler would say the crurotarsans. 
It's not that the dinosaurs weren't doing well. The crurotarsans 
were doing more," Brusatte said.