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Profitable Wonders by James Le Fanu
C A M B R I A N TA L E S
Science’s ability to penetrate deep into the unimaginably distant past never ceases to amaze. It is impressive enough that we can trace our human lineage all the way back to our earliest ancestors on the plains of the African savanna three million years ago. But traversing the aeons of preceding time, palaeontologists can now provide a comprehensive account of the whole range of complex life forms that emerged during the Cambrian period 530 million years ago – so long ago that in the interim the glacial movement of the tectonic plates beneath the earth’s surface has had time enough to elevate the depths of the oceans to the soaring peaks of the Rocky Mountains.
This notion of the Cambrian ‘explosion’ of life is scarcely novel. Victorian geologists tapping away at ancient rocks with their hammers were forcibly impressed by the dramatic transition from strata empty and devoid of life to those filled, from apparently nowhere, with the sudden influx of billions upon billions of fossilised remains.
It was not until the first decade of the twentieth century that the opportunity arose to examine those fossils in the detail necessary to recognise their unique and striking characteristics. In 1909 Charles Walcott of the Smithsonian Institution in Washington was returning from an expedition in the Rocky Mountains when his (pregnant) wife’s horse stumbled on a rock – prompting him to split the offending boulder with his hammer, revealing a profusion of the most perfectly preserved fossils ever encountered. Since then palaeontologists have dug out, scrutinised and categorised 70,000 specimens from the Burgess Shale, as it is known, and from more recently discovered sites in Siberia and China, the highlights of which Simon Conway Morris describes in his book The Crucible of Creation.
We start with the ‘mud dwellers’ in the ocean floor featuring the ‘efficient and dangerous’ worm-like predator Ottoia whose retractable proboscis sucks its prey towards its mouth, where a formidable array of sharp teeth pointing inwards and downwards extends, astonishingly, into the upper line of the digestive tract – ensuring there can be no escape. Then we encounter the remarkable variety of sponge-like ‘mud-stickers’ fixed to the ocean floor, such as Dinomischus, which resembles a daisy with a long stalk topped by a goblet-shaped body formed from a palisade of plates, each covered by numerous minuscule hair-like cilia that strain the sea water from food. Next we meet the extraordinary bestiary of ‘strollers walkers and crawlers’, including the famed trilobite with its armoured carapace, and Hallucigenia, so called because of its ‘bizarre and dreamlike appearance’, propelling itself on seven sets of stilts, echoed by seven tentacles protruding from its back. And finally there are the ‘swimmers and floaters’ such as the darting lancet-like Pikaia that moves by flicking its body in a series of rapid side-to-side undulations.
‘It’s been a bad week for you Charlie –
Arsenal losing again and now this’
The exuberance of these fossils seems to contradict the common perception of the Tree of Life starting off simply enough before diversifying into ever more sophisticated and complex forms. But its true significance is even more profound.
The main virtue of the scientific method is its ability to reveal the hidden and unifying reality behind appearances – no more so perhaps than in recognising that the millions of species with which we share the planet, and the vastly greater number long since extinct, can all be categorised as belonging to just one or other of a limited number of basic ‘body plans’. Thus while the diverse forms of insects (butterflies, beetles, flies, ants and so on), crustaceans (crabs, lobsters, shrimps) and arachnids (notably spiders) could scarcely be more distinct, they are all arthropods built on the same plan: segmented bodies consisting of a head, thorax and abdomen, six or more legs, and an external exoskeleton. This is in marked contrast to, for example, the very different body plan of the legless worms, with their long cylindrical tubelike bodies, or the echinoderms such as the starfish or sea urchin, defined by the radial symmetry of their five or more similar parts. And then there are the chordates with a backbone, spinal cord and complex circulatory and nervous systems, that encompass the millions of species of fish, reptiles, birds and mammals (including ourselves).
The most astonishing of all the extraordinary observations to emerge from categorising these fossilised forms of life that arrive ‘from apparently nowhere’ during the Cambrian explosion, is that each of these basic ‘body plans’ is represented. ‘Let us seek to fathom those things that are fathomable,’ observed the great poet and naturalist Goethe, ‘and reserve those things which are unfathomable for reverence in quietude.’
14 THE OLDIE – November 2011