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(Another)New Theory on Dinosaur Extinction

Hi everyone:
I saw this on the CNN Web site this morning. Please read, I am
interested to hear comments. Oh, I like disaster themes too :)

French Expert Says
           Sea Killed Sensitive Dinosaurs

           Reuters
           10-MAY-98
           By Crispian Balmer

           PARIS, May 11 (Reuters) - Sitting in his dusty fossil-filled
           office, Leonard Ginsburg believes he knows why the dinosaurs
           vanished 65 million years ago.

           The trouble is, few people outside France want to listen.
           Ginsburg, professor of palaeontology at the French Natural
           History Museum, published his first thesis on the extinction
of
           the dinosaurs more than 30 years ago.

           He believes his basic argument, that a gradual drop in world
sea
           levels led to disastrous climate changes for the huge
reptiles,
           still holds good but that more eye-catching theories have
           captured the public imagination.

           His main bug-bear is a U.S. hypothesis that the dinosaurs
were
           wiped out after a giant meteorite smashed into the Earth with
a
           force estimated at five billion times that of the Hiroshima
           nuclear bomb.

           ``This is ridiculous,'' Ginsburg says. ``It is obvious the
dinosaurs
           died over the space of millions of years and not in one
           cataclysmic event. The trouble is Americans like wonderful
           disaster scenarios and my idea is not spectacular enough.''

           Ironically, says Ginsburg, solid evidence that the dinosaurs
           slowly dwindled into oblivion rather than blasted off the
face of
           the Earth by a meteorite has been found in the United States
           itself, in fossil sites in the state of Montana.

           Digs have shown that 75 million years ago there were 30
species
           of giant reptile living in the area. Five million years later
there
           were 23, within two million years the number had fallen to
18,
           and so on down until the end of the so-called Cretaceous
period
           when all the dinosaurs had died out.

           DEATH AND RENEWAL While most people know that the
           dinosaurs died, few realise that the Earth's history has been

           marked by a succession of mysterious periods of
mass-extinction
           when whole families of animals disappeared for good.

           In addition to the extinction at the close of the Cretaceous,
other
           ``big killers'' took place at the end of the periods known as
the
           Permian (245 million years ago), Devonian (360 million years
           ago), Ordovician (438 million years ago) and the Cambrian
(510
           million years ago).

           Ginsburg believes that a common element probably tied all of
           these events together -- sea movement caused either by
changes
           to the polar icecaps or shifts of the Earth's crust.

           ``Each major division in the geological time-scale begins
with
           the spread of sea over land areas, accompanied by the
           appearance of new fauna, and ends with the sea shrinking
again
           which causes a massive loss of life,'' Ginsburg says.

           What was remarkable about the sea's retreat during the
fateful
           Cretaceous period was the scale of the move.

           Water used to cover most of Europe, all of North Africa, the
           Sahara, the Middle East and a large chunk of northwestern
South
           America.

           Then the seas inched back from their original coastline, most

           notably in Europe where the waters receded thousands of
           kilometres (miles), to end up close to their present shores.

           The dramatic change annihilated 80 percent of life on Earth,
           killing off not just the dinosaurs but a whole range of
species on
           land and in the sea, Ginsburg says.

           One of the most famous marine victims were ammonites, the
           beautiful spiral molluscs so beloved of fossil hunters which
had
           survived for 300 million years before succumbing to
extinction
           as their shallow water habitat got sucked away.

           But why were land-based dinosaurs affected by the sea? GIANT
           DINOSAURS SENSITIVE AT HEART As more land became
           exposed, so the world's climate was transformed.

           ``The previous tropical climate became increasingly
continental,
           bringing wider differences between winter and summer and
           between night and day. The dinosaurs simply could not cope,''

           said the white-haired professor.

           To demonstrate their sensitivity to temperature, Ginsburg
points
           to the alligator -- which only just managed to claw its way
out of
           the Cretaceous period.

           Tests have shown that between 32 and 34 degrees centigrade
(89
           and 93 degrees Fahrenheit), incubating American alligator
eggs
           will only hatch as males while between 28 and 30 centigrade
           (82 and 86 degrees fahrenheit) they produce females.

           ``If such a small temperature drop is enough to ensure that
no
           male alligators are born, the drop of about eight degrees
           centigrade seen in the late Cretaceous period was surely
enough
           to eliminate entire reptile groups -- specifically
dinosaurs,''
           Ginsburg maintains.

           Warm-blooded animals, like mammals, managed to survive the
           cooler climes. Reptiles, which are cold blooded and highly
           susceptible to the surrounding temperature, struggled to
adapt
           and most perished.

           ``Dinosaurs were like oil tankers. They needed a long time to

           change course and ultimately never made it,'' Ginsburg said.

           A DINOSAUR THEORY A WEEK Any number of theories have
           been put forward in recent years to try to explain one of
           science's oldest enigmas.

           These include a proposal that dinosaurs reached a saturation
           point in their evolutionary process, with their heads
becoming
           too small for their body to cope with.

           Another idea from India argues that intense volcanic activity
on
           the sub-continent threw up so much ash into the atmosphere
that
           it blocked the sun, killing much life on Earth.

           ``In the past 30 years, several theories have been put
forward
           about the end of the dinosaurs. None of the authors has
criticised,
           discussed or even mentioned my theory,'' he said. ``I think
that
           anything not written in English is ignored.''

           The explanation most often cited involves the killer comet --
a
           view first aired by U.S. geologist Walter Alvarez in 1980.

           He argued that large amounts of the metallic element iridium
           found in sediments deposited at the end of the Cretaceous
period
           indicated that a huge meteorite had struck home.

           A rare element, iridium is found in abundance on meteorites.
           Alvarez believes a chunk of the extra-terrestrial matter hit
Earth
           with such force it raised a suffocating dust cloud which
spread
           iridium around the globe and shut out the sun for years.

           But Ginsburg argues that the iridium could equally well have
           been left by the pockets of evaporating water.

           ``In a century of speed and noise, my theory based on a slow
           moving phenomenon has less appeal than its rival,'' he said.

           Disappointed by his failure to gain a global audience for his

           dinosaur theory, Ginsburg has now switched his attention to
the
           less controversial field of the early rhinoceros. ``It's a
much
           more civilised, peaceful area of research,'' he said.

--
Matt Morgan
Mile High Meteorites
http://www.mhmeteorites.com
P.O.Box 151293
Lakewood, CO 80215-9293
"For a geologist, life is a field trip"