Horizon 2002 The Mystery Of The Jurassic + English subtitle

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Horizon 2002 The Mystery Of The Jurassic

Information

The Mystery of the Jurassic BBC Two 9.00pm Thursday 28 March 2002

\"For years scientists have been trying to find the mysterious evolutionary
master key responsible for transforming the dinosaurs into world-beaters\"

In the early Jurassic, 200 million years ago, they were a relatively small
group of primitive creatures. By the late Jurassic, 50 million years later,
they had become the magnificent array of carnivores and giant plant eaters
that would dominate the planet for millions of years. In between lies the
mysterious period of the middle Jurassic in which all these changes must
have happened. But what were they? What was it that transformed the
dinosaurs?

Was there some terrible mass extinction? Had there been an amazing change in
the environment? All this was speculation and theory. How and where would
evidence come to light? Fossils from the middle Jurassic are incredibly
rare. All anyone had to go on were a few small outcrops of rock dotted
around the world.

Remarkable evidence

Then a treasure trove of fossils emerged from the midst of an Argentinian
wilderness in the 1990s; thousands of square miles of mid-Jurassic rocks. On
their first season in the field, palaeontologist Oliver Rauhut and his team
unearthed two giant meat-eating dinosaurs and six huge long-necked
dinosaurs. And there was much more: early mammals, crocodiles, fish and even
plant life. They had uncovered a complete mid-Jurassic eco-system, a
wonderful snapshot of life from this dark age of dinosaurs.

\"It's as if someone has unearthed a holy grail of dinosaur palaeontology,\"
says British geologist, Dr Phil Manning. Oliver Rauhut describes the site
as, \"an extraordinary window on the mid-Jurassic.\"

Above all, the hope is that this site may contain all the information they
need to find the mysterious evolutionary forces that have eluded
palaeontologists for so long.

No mass extinction?

Already they've been able to test out many of their theories and draw some
exciting conclusions. For instance, one theory about what might have
happened in the mid-Jurassic clearly does not seem to be supported by the
finds in Argentina: the mass extinction theory.

The laws of evolution say that a major extinction event could have caused an
explosion in dinosaur diversity like the one in the mid-Jurassic. Death on
such a vast scale clears away the competition, allowing the survivors to
evolve rapidly into new ecological niches. But there's no evidence in
Argentina for an extinction event affecting the dinosaurs.

A second theory was that a major climate change could have transformed the
dinosaurs' environment, leading to the evolution of many new types of
dinosaur. In Argentina there is indeed evidence for a dramatic change in the
climate. At the time of the early, primitive dinosaurs all the continents
were gathered together in one giant super-continent (Pangea). The climate of
the super-continent was dominated by extremely hot and dry conditions - with
rainfall concentrated in a short bursts. Scientists call this the time of
the mega-monsoon. Then in the middle Jurassic Pangea began to split apart.
The Argentinian site offers evidence that as the super-continent split up,
the climate changed to a more moderate, less extreme climate.

Barriers to migration

Many scientists believe that on its own climate change isn't enough to
explain what happened to the dinosaurs in the mid-Jurassic. As Phil Manning
points out, the dinosaurs could in theory simply move to find the climates
they were most adapted to - unless something stopped them from moving, some
major physical barrier that meant they couldn't follow the climate zones.
When scientists looked into this, it became clear that as the
super-continent split up, such a barrier was being formed. Today it's called
the Atlantic Ocean.

This major barrier would allow an evolutionary process called vicariance to
operate - animals on different sides of the barrier are able to evolve
separately. The problem was there was no proof of vicariance in the
mid-Jurassic. Until Argentina.

Fortunately the site has fossils from just before and just after the
super-continent split in two, so it's ideally placed to judge whether
vicariance was beginning to take effect. And the early results are lending
support that this may have been a key factor in explaining what happened to
the dinosaurs in the mid-Jurassic.



Technical Specs

Video SourceVBc > MPEG2 > Divx
Video Codec: Divx 6
Video Bitrate: 1855 kb/s
Video Resolution: 688x512 (1.34:1)
Video Aspect Ratio: 4:3
Audio Codec: MP3
Audio BitRate: 128 kb/s (64/ch) CBR 48000 Hz
RunTime: 49m 10s
Part Size: 699mb