Saturday 16 December, 2000
Unearthing The First Vertebrates
Could something that resembles an animated anchovy fillet be the ancestor of most modern groups of animal?
In Life Story, producer Martin Redfern travels the world in search of fossils that record key events in the history of life. Here he reports on his journey of discovery to south-west China, where geologists and palaeontologists have unearthed exciting fossil finds.
Burgess Shale, Canada
As you journey down through layer after layer of sedimentary rock, you travel back in time. The further you go, with a few notable exceptions, the rarer fossils become and the more poorly they are preserved. In 1909, the American palaeontologist Charles Walcott discovered one of the notable exceptions in what is called the Burgess Shale on a hillside in British Columbia in Canada.
The Burgess Shale is of the Cambrian period, more than 500 million years old. And the fossils within it caused amazement among scientists and culminated in Stephen Jay Gould’s book Wonderful Life. In it he describes the explosion of life forms in the Cambrian period, creatures so fantastic that they are impossible to classify into present-day animal groups. Over the last 10 years however, palaeontologists have slowly made sense of them and found within the Burgess Shale ancestors of most of the modern animal groups.
What is most striking about Cambrian fossils everywhere, particularly when they are compared to the older Pre-Cambrian Ediacaran creatures, is how active they all were. Worms are burrowing into the mud, molluscs are building elaborately patterned shells and a host of fierce looking arthropods are swimming in the sea. Perhaps they were the reason for the shells and burrows.
| ‘They were the world's first predators and would gobble up any soft creatures that did not hide or protect themselves.’ | |
Yunnan province, south-west China
Fantastic as the Burgess Shale fossils are, there are now even more exciting Cambrian fossils coming to light, this time from China, so it was with great excitement as I set off for Kunming in Yunnan province in south-west China. It is a bustling modern city and many of the old buildings and tree-lined avenues have been bulldozed to make way for motorways and high-rise hotels. But it is still clear from the climate and the fertile green hills around it why Kunming has been called the city of eternal spring.
Before long had I met up with my geological guide, Professor Luo Huilin from the Yunnan Institute of Geological Sciences and we were driving south among the fields. We were heading for a hillside famous among palaeontologists just outside the town of Chengjiang.
Here, thousands of fossils have been found which are slightly older and even better preserved than those in the Burgess Shale. Unlike the Burgess Shale fossils which have been squashed and cooked deep in the Earth's crust, the rocks of Chengjiang have not been changed much over half a billion years. The remains of creatures within them show up as an attractive red- brown against the greys and greens of the shale and, with painstaking work under the microscope, the Chinese palaeontologists have almost been able to dissect them layer by layer, investigating their internal organs.
Anomalocaris and Yunnanozoon
As in Canada, there is a rich fauna, particularly of arthropods - little shrimp like creatures, trilobites that look like big wood lice, and a giant crab called Anomalocaris, up to a metre long and able to feed off just about anything else. These were indeed fierce creatures.
But most excitement has been caused not by the heavily armoured arthropods but by a range of insignificance-looking lancet-shaped fossils. At least some of these are believed to be chordates, members of the large group that has few primitive members today but also includes all vertebrates - fish, reptiles, mammals and even ourselves.
Hundreds of specimens of a creature called Yunnanozoon have been discovered. While some believe they are more primitive, perhaps even just worms, my Chinese hosts are sure that they are chordates, creatures like animated anchovy fillets with a rudimentary nervous system along a spinal cord plus gill slits and the typical zigzag muscle blocks of vertebrates.
Last year, the discovery of two more fossils near the village of Haiku, nearby, caused even more excitement and controversy. Most palaeontologists believe that these are primitive fish similar to lampreys and hagfish still found living today. Though they have no bones or jaws, these could be among the earliest representatives of the vertebrate group that includes fish and humans.
Perhaps not surprisingly, my guide did not want me to take my geological hammer out and start an intensive fossil hunt in the classic Chengjiang section. Instead, he took me to a beautiful valley just north of Kunming City, named after the nearby Bamboo Temple, Qiongzhusi. Here grey lower Cambrian shales are exposed and after only a few minutes searching I started to find the little head shields and segmented bodies of trilobites, all now extinct. These were early experiments in evolution that ultimately failed, leaving those little animated anchovy fillets and their descendants to inherit the Earth.
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| Penguin first published Stephen Jay Gould’s book Wonderful Life in 1991. Earlier this year a new edition was published by Vintage. |
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