[meteorite-list] Dino 'Survival' Claim Disputed

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:20 2004
Message-ID: <200402051640.IAA25609_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/2/hi/science/nature/3458651.stm

Dino 'survival' claim disputed
By Paul Rincon
BBC News
February 5, 2004

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."
Received on Thu 05 Feb 2004 11:40:00 AM PST