Trilobites emerged fully formed upon the Cambrian scene. By the time, some 521 million years ago, that the initial members of this ancient line of arthropods began filling oceanic environments around the globe, they were already creatures with highly developed eyes, complex digestive systems and admirably functional calcite carapaces. Quite simply, at that moment trilobites were the most advanced life forms that Planet Earth had ever produced.
Despite their sudden and dramatic appearance in the fossil record, it is obvious that trilobites evolved from earlier, more primitive organisms. Many of these ancestral creatures may have more resembled segmented worms or articulated jellyfish than the distinctive three-lobed animals that we all recognize today. Those possible early ancestors, such asSprigginafloundersi --found in the 550 million year old Ediacaran-age rocks of Australia -- appear to have possessed rudimentary body segments and even primitive genal spines. But despite such somewhat recognizable evolutionary advances, these primeval life forms were a far cry from the Redlichid trilobites that some 30 million years later would dominate the world's seas.
The truth is that the fossil record has guarded the secrets of early trilobites -- and their immediate predecessors -- with a steadfast passion. Indeed, only a scarce few locations across the face of the planet have so far revealed themselves to be the cradles for these early “experiments” with complex life. In recent years, discoveries made in outposts such as the fossil-rich Chengjaing formation of southern China and the trilobite strongholds of central Nevada have cast additional light on this poorly understood period of earth history. But the hunt for the World's Oldest Trilobites rages on.
One of the prime candidates for producing the initial members of the trilobite lineage lies in the remote Siberian outcrops of eastern Russia. There, localized species such asProfallotaspisandBigotinaappear to stand at the very base of the entire trilobite family tree, creatures that more than half a billion years ago provided ample proof that complex, multi-cellular life could indeed survive on this “hostile” planet called Earth. Early members of the trilobite line were almost simultaneously emerging in other hot-spots around the globe, as evidenced by sedimentary outcrops recently found in Spain, California and Morocco. Yet in terms of their sheer primal heritage, few, if any, of these now disparate locations present material rivaling what is currently being discovered in those ancient Siberian formations.
Interestingly, not all of these early trilobite locales shared a similar climate; Siberia lay squarely within a tropical zone near the ancient equator, while the Moroccan and Spanish outcrops were then to be found in southern seas far more temperate in climate. Science is yet to present a comprehensive analysis of the role Cambrian water temperatures may have played in the development of the trilobite line. But it seems a virtual certainty that a hospitable climate played a vital role in the successful emergence of these ancient arthropods.
However, even if we choose to debate the exact location where the first trilobites reared their antennae-adorned cepahlons, there is no doubt that a mere “instant” later in geological time, trilobites would be in the midst of perhaps the most fertile period in their entire history. Thousands of new species, including the likes ofGabriellus kierorum,Bristolia bristolensisandOlenellus fremontiwould soon help to firmly establish a class of animals that would survive for the next 270 million years.
Snowball Earth
It ranks among the most intriguing questions in the entire paleontological canon: What were the events that triggered the famed Cambrian Explosion some 540 million years ago?
Was that planet-changing phenomenon caused by a meteorite strike that “seeded” the Earth's oceans with a flood of bio-matter? Was it caused by the spewing forth of nutrient-rich plumes from a field of undersea volcanoes, or by lightning bursts which electrified the planet's amino acid-laced atmosphere? Was it the work of some Supreme Being's creative hand?
Over the years, all of these theories - and many more - have been presented in an attempt to explain the sudden blossoming of complex life on our world… a biological blooming that followed fourbillionyears of virtual inactivity. And, in fact, some of those speculations may even hold a loose grip on the proverbial “smoking gun” when it comes to properly answering such a momentous question. However, it was only during the latter days of the 20th Century that a particularly fascinating hypothesis began to take shape, one which possibly offered the best explanation yet for this unprecedented outbreak of life.
It was then postulated that at some point significantly prior to the dawning of the Cambrian Period - possibly as far back as 700 million years ago -- the planet had become completely entrapped within a layer of ice, a phenomenon that has since become popularized under the catchy moniker Snowball Earth. Science has long known that our world has been subjected to fluctuating periods of glaciation and subsequent warming, but to the best of our admittedly limited knowledge, none of these other “ice ages” featured a stage during which the entire planet had become frozen from pole to pole.
From the moment of its inception, this “frozen planet” theory had both its ardent supports and its equally vociferous detractors. Proponents quickly voiced their belief that such a theory would help explain the elevated sea levels that characterized the Cambrian… with the thawing of globe-covering ice sheets subsequently providing a more hospitable -- and wide ranging -- aquatic environment for the arthropod armies soon to follow. Those who questioned Snowball Earth, however, countered that a complete glaciation of the planet, particularly a freeze that lasted for tens-of-millions of years, would have created a particularly unforgiving global habitat, one in which primitive life forms would have faced difficulty developing and surviving, let alone thriving.
Yet those who supported the Snowball Earth hypothesis insisted that marine volcanic activity - believed to be rampant world-wide both late in the Precambrian and throughout the Cambrian itself - would have eventually served to both counteract, and slowly begin to reverse the more drastic aspects of such an “ice world”. In addition, they pointed out that these volcanic conditions might well have acted as the needed catalyst for the development of complex life in the primeval oceans. Indeed, even today we see a somewhat similar phenomenon happening on a much less dramatic scale in areas adjacent to undersea fumaroles.
So while we are now better able to address the question of what events may have served to trigger the Cambrian Explosion, it seems that the myriad natural causes involved with this phenomenon remain cloaked in a shroud of mystery. And in light of our current obsession with Global Warming, we must also wonder if the conditions required for the advent of an ice planet scenario could ever again rear their frosty fingers.
Considering that Snowball Earth may have lasted for over 100 million years, it would seem safe to say that any return engagement would effectively end life - or at leasthumanlife - on our world. If such a disastrous scenario were indeed to occur again, perhaps we could then compress the last 540 million years of Earth history into one short sentence: What the planet had giveth, the planet had thus taketh away.
Here's a look at some of the first trilobites in the fossil record:
Cambroinyoella wallacei:Similar to the species above, this example from Nevada shows that early trilobite radiation was a wide occurrence.
Jakutus primigenius:A Siberian species that represents one of the oldest lines of trilobites.
Olenellus nevadensis: Anelegant member of one of the oldest trilobite families.
Redlichia chinensis:This attractive pair of early trilobites provides evidence of the species' prolific nature.
Gabriellus kierorum:A magnificently preserved Lower Cambrian trilobite found in British Columbia, Canada.
Bristolia bristolensis:From California's Marble Mountains, this Lower Cambrian species is one of America's oldest trilobites.
Archaeaspis macropleuron:One of the earliest trilobites, this species is found in Nevada and displays features of BOTH the Redlichid and Olenellid lines.
Bolbolenellus brevispinus:An unusual member of the Olenellid line.
