Dino 'survival' claim disputed

[Garrison Hilliard <garrison@efn.org>]

Dino 'survival' claim disputed 

By Paul Rincon 
BBC News Online science staff 

The idea that dinosaurs survived for some time after the asteroid impact blamed
for wiping them out 65 million years ago has been dealt a blow. 
Dinosaur egg fragments dug out of rocks in China seem to postdate the dramatic
extinction event popularly believed to have extinguished the creatures. 

But new data suggests the egg pieces got mixed up in later deposits through the
action of mud and debris flows. 

Details of the latest findings are published in the Journal of Geology. 


Dinosaurs survived until the end of the Cretaceous Period of Earth history. But
by the beginning of the Tertiary Period, about 65 million years ago, they had
apparently vanished. 
Egg discovery 

At numerous sites around the world, a clay layer separates rocks laid down in
the Cretaceous from those deposited in the Tertiary. This is known as the K-T
boundary. 

The boundary contains high concentrations of the element iridium, commonly found
in meteorites. Researchers have proposed that a meteorite impact which produced
a huge crater at Chicxulub in Mexico, could have been responsible for the demise
of the creatures. 

Discoveries of dinosaur egg fragments in deposits from Nanxiong Basin, southern
China, which contain Tertiary animal remains and pollen, suggested dinosaurs
there could have survived until about 62 million years ago. 

But US and Chinese researchers now dispute this. 

They claim the egg pieces originated in Cretaceous deposits and were swept up in
mud and debris flows during the Tertiary. This jumbled material was then
re-deposited. 

Dr Brenda Buck of the University of Nevada, Las Vegas, US, said she came upon
the idea while examining palaeosols, ancient soils that have been buried and
later exposed in Nanxiong. 


"During the dry season you had these big open cracks," she explains. 
"Mudflows would come down and fill in those cracks. All those mudflows are in
the [rock] sections where the flora and fauna are mixed." 

Dr Buck suggests the presence of several iridium layers at Nanxiong supports a
view that Cretaceous rocks were reworked in the Tertiary. 

Multiple claims 

There have been other claims for the survival of dinosaurs into Tertiary times
at sites in Montana and New Mexico in the US, in Bolivia and in India. 

All of these claims have been questioned by other researchers. 

"The only really well documented dinosaur remains are from the American west. We
actually have no idea what's happening anywhere else in the world," Dr Norman
MacLeod, keeper of palaeontology at the Natural History Museum in London, told
BBC News Online. 

"We know that they lived on other continents, so there's no particular reason to
suppose that that western US population was the last population. 

"It could well be that they went above the K-T boundary in other parts of the
world, especially parts that were remote from the Chicxulub impact." 


Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/3458651.stm

Published: 2004/02/05 10:31:59 GMT

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