[meteorite-list] Giant Dinosaurs Arrived With A Bang

From: George Winters <meteorites_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:49 2004
Message-ID: <5.1.0.14.2.20020516144506.033bacf8_at_stonejungle.com>

I always love to debate this issue of impact caused extinction. There is
no doubt that an asteroid or some large body struck the earth about 65
million years ago (and many times prior to that event). But the fact that
the event happened, does not prove that it was the sole cause for the mass
extinction.

There are to many holes in the theory. My favorite example, is that the
creatures that should have been severely affected such as birds, frogs,
turtles and many forms of microscopic life, in fact survived the
event. These animals and plants are very sensitive to their
environment. Today we are loosing many species because of much less severe
changes to habitats Then a large impact would cause. I feel that it is
more likely that the impact contributed to the extinction of already
weakened groups such as the dinosaurs and other marine and flying reptiles.

At 12:56 PM 5/16/2002 -0700, you wrote:


>http://www.newscientist.com/news/news.jsp?id=ns99992290
>
>Giant dinosaurs arrived with a bang
>New Scientist
>May 16, 2002
>
>Dinosaurs may have arrived with a bang, as well as gone out with one.
>Scientists have found the hallmarks of a meteorite impact and mass
>extinction in rocks just below strata containing the earliest footprints of
>large meat-eating dinosaurs.
>
>The finding of high levels of iridium metal and fossilised fern spores
>suggests that a sudden extinction cleared the ecological stage, leaving room
>for meat-eating dinosaurs to grow suddenly larger. A subsequent, massive
>meteorite impact about 65 million years ago resulted in the extinction of
>the creatures.
>
>Dinosaurs evolved about 230 million years ago and competed with many other
>reptiles until the Triassic period ended about 202 million years ago. Then
>most of the competitors vanished and dinosaurs grew to their
>characteristically monstrous proportions in the Jurassic period that
>followed.
>
>The key to how the dinosaurs came to dominate the land in this way may now
>have been discovered in the sedimentary rocks laid down over the
>Triassic-Jurassic boundary in what is now northeastern North America.
>
>Devastated landscape
>
>The rocks contain few fossil bones, but they preserve both fossil pollen and
>the footprints of animals that walked beside ancient lakes. Lake levels rose
>and fell with periodic climate cycles, so the rocks can be finely dated,
>says Paul Olsen of the Lamont Doherty Earth Observatory of Columbia
>University.
>
>Surveying 80 sites, Olsen's group found that fossil footprints changed from
>typical Triassic to typical Jurassic groupings in a period of just 50,000
>years. In between lay the boundary between the periods, defined by a change
>in pollen type, and including the layer rich in iridium and fern spores.
>
>The fern spores are indicative because ferns spread rapidly over devastated
>landscapes - sharp peaks of spores also occurred just after the final,
>cataclysmic impact 65 million years ago.
>
>Eat anything
>
>The faunal change was also sharp. "In the late Triassic, there were lots of
>different footprints representing many different reptile groups," Olsen told
>New Scientist. Yet at the start of the Jurassic "all you see are dinosaurs,
>lizards and very small, fully terrestrial crocodiles".
>
>And the size of the dinosaurs jumps sharply. Just 50,000 years after the
>start of the Jurassic, there are tracks of Eubrontes giganteus, a six-metre
>long predator that Olsen says was nearly twice as massive as the biggest
>Triassic dinosaur.
>
>The meat eaters survived the disaster probably because of their adaptable
>diets, says Olsen. It is typical for a "decimated ecosystem" to become
>dominated by animals that can survive on whatever they can find, he says.
>
>Instead of hunting plant-eaters, "they're primarily hunting other carnivores
>and things in the water," such as fish. Not until about 100,000 years after
>the extinction did a few small plant-eaters start leaving their footprints
>by the lakes.
>
>Michael Benton of the University of Bristol aggress that the rapid change in
>seen in the dinosaurs suggests "it was more of a catastrophic event than
>people had thought". However, he warns that Olsen's group has studied only
>one area, while iridium-rich deposits from the impact 65 million years ago
>have been found at 200 different sites.
>
>Journal reference: Science (vol 296, p 1305)
>
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Received on Thu 16 May 2002 05:03:58 PM PDT