The fall of the trilobita
Mass extinction at the end of the Permian
"Long before the age of fishes, which began about 400 million years ago, the trilobites had already survived evolutionary decimation by about 170 million years. The span of time which saw the birth, development and disappearance of trilobites and their age is indeed staggering." - Riccardo Levi-Setti
For almost 300 million years trilobites roamed across the sea floors of the Palaeozoic, playing a sometimes predominant role in the ecology of their particular habitats and influencing life in the ancient oceans. But, as with all good things, their apparently never-ending existence finally had to come to an end. They managed to survive several global ecological disasters, ranging from considerable changes in the world’s climate to major geological processes and the apocalyptic bombardments of the Earth by meteorites and asteroids by adapting to new environmental conditions and successfully defending against old and new natural enemies. It was not until the inferno at the end of the Permian, some 251 million years ago, resulting in the complete extinction of approximately 70% of all land animals and a disastrous 90% of all marine life forms, that the class of the trilobita was finally facing extermination. With the fall of the trilobita, one of the most successful life forms ever disappeared off the face of the Earth for good.
But why, after surviving for such an enormous period of time, could they not take that final hurdle that nowadays marks the border to the Mesozoic? One reason can be found in the very series of catastrophies mentioned above, the fatal one at the end of the Permian being simply the straw that broke the camel’s back. Trilobites finally had to pay dearly for their never-ceasing struggle for survival. At their best times having more than sixty families during the Upper Cambrian, they declined in numbers continuously. In the course of several global mass extinctions which naturally also took their toll on the trilobites, existing families were reduced to a mere one third during another extinction level event at the end of the Ordovician. And at the end of the Devonian, a meagre five families – all belonging to the resilient class of the Proetida – had managed to survive, three of which taking up the final battle in the End-Permian mass extinction.
Such a dramatic decline in biological diversity to a sheer minimum became the headstone to the drama that was to follow. The smaller the amount of species and population, the higher the risk of extermination with even small causes. The Permian catastrophy merely added to the accumulation of hostile circumstances which broke the neck of our little friends (only literally, of course, as our bugs were invertebrates). Changes in ecology, the biological mechanisms of displacement by other life forms and new patterns of hunter-prey relations all worked together to eradicate trilobites from the seas of the End-Palaeozoic.
"For a species to be rare means to always be close to the brink of collective collapse." writes David Quammen in his recommendable book The Song of the Dodo : At some time after the terrible apocalypse at the end of the Permian the last surving trilobite, perhaps a member of the genus Acropyge, was holding out in a dark corner of its habitat. Following the global catastrophy food had become very, very scarce. There was hardly a living thing. The world’s oceans were close to being biologically dead. During the last two years our little trilobite had not met a single fellow bug. But neither it nor anyone or else knew that it was actually the last of its kind, the last of its species, its family, its order, its class. Another day dawned – dawned darkly as all days had done in the months following the asteroids impact as huge amounts of material had been thrown into the planet’s atmosphere, shielding the world’s biosphere from the warming rays of the sun – and the trilobite’s instinct left it with no choice but to leave its protective hide-out to look for food. A marine predator, itself now a maverick and on the brink of starvation, detected its presence and ended its lonesome life in a single, hungry bite. That’s what extinction looks like!
A very sad story, indeed, and told in a sad manner (for which I ask forgiveness), a story, nevertheless, which is being replayed day after day after day: Species, families, orders and entire classes face extinction as we speak. Roughly one hundred species – many of them arthropods - vanished forever from the face of planet Earth during the last twentyfour hours. Another one hundred species won’t live to see another day.
Yet today it is mostly man who bears responsibility for the extinction of many of his fellow creatures. Torwards the end of the 17th century, it took us no more than seventy years to completely eradicate the Dodo [Raphus cucullatus (LINNAEUS, 1758), an innocent, flightless and fatally confiding bird of the family of doves, living as an endemic species on the island of Mauritius. Sailors killed them by the thousands, for food but also just “for the fun of it”, as they were very easy targets.. Today we do not even know what the Dodo exactly looked like. Save for a few paintings (see ill.) and some dubious reports in writing there’s hardly anything left of the Dodo. The director of a British museum gave orders to burn the last complete stuffed specimen in 1755 as it had attracted “too much dust”. Human stupidity and ignorance is indeed unlimited.
Additional note, September 2008:
Merely by coincidence I stumbled upon a very extraordinary book the other day. Released in 2004 and receiving the European Publishers Award for Photography 2004 straightaway, the landscape orientated book brings the extinct Dodo back into existence. In a fascinating reconstruction of the past, Finnish photographer Harri Kallio uses his considerable photographic skill and imagination to create the illusion that these fascinating creatures are alive and abundant, living as they once did in their own unspoilt haven, the island of Mauritius. Kallio's Dodos are featured in its landscape, near rivers, on mountains, in lush valleys and dense woodlands, undisturbed and blissfully unaware of the earlier human invasion which ultimately led to their extinction in the 17th century. The photographs are accompanied by a thorough history of the Dodo, including eyewitness accounts, pictorial sources and physical evidence from museums and libraries all over the world. There are only four museums that house true Dodo remains: Oxford University Natural History Museum, Natural History Museum London, Copenhagen University and the Zoological museum, Prague. Kallio used these resources, and many more, to meticulously research his subject, before carefully constructing his own, very accurate Dodo models!
Harri Kallio: The Dodo and Mauritius Island – Imaginary Encounters
Hardcover: 128 pages
Publisher: Dewi Lewis Publishing; 1. Edition: (Oct. 2004)
Size: 30.2 x 24.6 x 2.2 cm
Scientists in growing numbers come to the conclusion that the irreversible disappearance of many species during the last two hundred to three hundred years, as a direct result of our irresponsible behaviour, threatens to become a massacre the consequences of which only marginally differing from any of the extinction level events that haunted life on Earth in regular intervalls since the early Cambrian. The fossil record seems to indicate a time span of roughly ten million years following such an event for nature to recover to reach a pre-event status of biological diversity. Therefore the consequences of man’s destructive influence on fauna and flora surely will be incalculable and lasting
(Note: The most authentic portrayal of the Dodo can be found in the wonderfully illustrated book "A Gap in Nature" by Tim F. Flannery and Peter Schouten. The work revives many species, most of which having been exterminated by the hand of man.)
The average time of existence, the survival rate of a particular species, is but a few million years. Statistically, man, Homo sapiens, is already getting close to reaching the final stages of its life expectancy. Not too regretable, I guess, considering the aforesaid. Trilobites managed to survive for a much longer period. We do not need – nor do we have any right – to look for deficiencies and shortcomings within the trilobite clade which may have contributed to its total destruction. Trilobites were strong enough to survive for 295 million years, a performance matched by only a handful of other animal groups.
As already mentioned above, the recent analysis of large amounts of available data indicate that we are at the beginning of the sixth mass extinction event within the last 440 million years, if not already right in it, as many scientists believe it to be already in full swing. An extinction event caused by man. And we cannot expect the originator to manage to evade and escape its consequences. In order to do that we would need something we do not have, but which trilobites used to have in abundance: unambitious biological stubbornness and obstinacy.
For as far as the existence of Homo sapiens is concerned, one must never forget that man is not living in a status of being disconnected from nature. As a matter of fact he is a very part of it, in the sense that everything he does needs to be regarded as natural, including the dreadful deed of destroying other life forms and its very own means of existence by environmental pollution and destruction.
We like to regard ourselves as a very unique entity, for the most part unaffected by developments in our environment. Nothing could be further from the truth. The truth is that it was evolution itself which started its biggest experiment ever when it allowed the human race to play its predominant role. Once this experiment fails – and it will fail, it will – the “monkey in a suit and tie” will follow the path of all other creatures that disappeared from the face of the Earth. Not really that much regrettable, I’d say! This may sound like a philosophical approach to a very grave outlook but its simply the truth. I am inclined to find my personal quantum of solace in this conviction when listenting to the everyday bad news …
In one of his recent books (The Earth: An Intimate History) Richard Fortey closes the fifth chapter with a fitting remark on the human species, albeit in a somewhat different context: “The human race is but a parasitic tick, enjoying the present abundance and plenty for as long as the oceans stay on a low level and the climate comparably mild. But the current arrangement of land and sea will change and change will our short-termed predominance.” I have nothing to add.
The extinction of the trilobita marks the end of the Palaeozoic era, a mysterious world full of yet unsolved riddles, many of its fossilised hints still waiting to be deciphered. Trilobites for sure never anticipated the attention they would get from a particular species more than 250 million years after their leaving the stage of life. It is more than doubtful that the human genus will receive the same honours.
Last Update :
02/23/2010 6:36 PM
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