Those who posses a special fondness for trilobites have never been particularly intimidated by the concept of time. After all, in a field where millions of years are the standard means of measurement, and half a billion years is part of the lexicon, a well-honed “feel” for mind-numbing numbers appears to go right along with the Paleozoic territory.
Yet dealing with the age of trilobites… the age of our planet… the age of the universe, often seems beyond the realm of what our “primitive” brain can deal with. Sometimes we imagine we've got all these Cambrian Explosion, Snowball Earth and Punctuated Equilibria things figured out -- with all the adjacent, Plate Tectonic and Shifting Polarity mumbo-jumbo thrown in for good measure. Apparently, for a species that has existed in its present form for far less than a million years, and whose entire lineage can presently be traced back some 14 million years, we Homo sapiens can be an arrogant bunch.
Our latest technology now projects a 4.54 billion year age for our planet. Yet even in light of the ever-expanding frontiers being conquered by science, can we ever hope to fully digest the concept -- let alone the content -- of that overwhelming span of Earth history… or correspondingly, the roughly 520 million years that have transpired since trilobites began to roam ancient sea floors? To say the least, dealing with such numbers is an imposing task.
Despite the scientific import that trilobites have long held, some continue to dismiss these ancient arthropods as little more than a failed evolutionary experiment. Others, however, will note the impressive duration of the trilobites' passage through geologic time, as well as their incredible diversity, which saw over 25,000 scientifically recognized species end up inhabiting every available oceanic niche within their world. By doing so, they correctly acknowledge the esteemed trilobite as one of the most successful creatures ever to roam the face of Planet Earth. From the early elegance ofElliptocephala asaphoides, through the Silurian majesty of Arctinurus boltoni, to the end-of-the-line importance of Ameura major, it's virtually impossible to underestimate the role that trilobites have played in the history of this third stone from the sun.
So while the inherent limitations of the human mind may never allow us to fully comprehend the significance of an animal class existing and evolving for nearly 300 million years, those who look admiringly upon the trilobite lineage do their best to place such longevity into some kind of mentally manageable perspective. However, maybe we make too much of all this. Perhaps we simply weren't wired to ponder the number of stars in the sky… the multitude of sand grains on a beach… or the “deep time” age of the universe. Perhaps humans were never supposed to consider such weighty matters as the longevity of trilobites with a brain that too often forgets where we left our car keys or has trouble balancing a checkbook. Just maybe, when all is said-and-done, we can all find a degree of reassuring truth in what the old cliché (and Albert Einstein) has long told us… time is all relative.
To better understand these concepts, let us use the world's best known Mesozoic inhabitant, Tyrannosaurus rex. This legendary dinosaur became extinct 65 million years ago... while in contrast, trilobites emerged more than 500 million years ago. Then to put the astonishing parameters of Geologic Time in a proper perspective, consider the following: the last trilobites (proteids) swam in the Permian oceans some 251 million years ago. This was 186 million years before Tyrannosaurus rex left its initial footprint on our planet.
This link displays the current Geologic Time Scale, which serves as a reference for study of the trilobites on this website.
The Paleozoic Era
A mere listing of geologic periods cannot begin to convey the singular significance of the Paleozoic Era. After nearly four billion years of spinning through the cosmos as a virtually barren ball, Planet Earth suddenly sprung to life at the dawning of the Paleozoic. It was a time that witnessed the most rapid development and diversification of multi-cellular organisms in earth history -- an event that signaled the beginning of the famed Cambrian Explosion.
The Paleozoic lasted for nearly 290 million years… from 541 to 252 million years ago. Science has chosen to divide that incomprehensible length of earth history into seven geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian and Permian, each of which not only featured its own unique flora and fauna, but also apparently its own natural disaster which seemingly signaled that period's beginning… or subsequent end.
Trilobites served to neatly bookend the Paleozoic, arising in the Lower Cambrian, some 521 million years ago, and lasting until the end of the Permian. But these amazing arthropods were far from the only creatures living in those ancient seas. In the Cambrian, a time when the oceans dominated the planet and surrounded the short-lived supercontinent of Pannotia, such trilobite species as Olenellus transitans were joined by a plethora of other invertebrates. Many of these were soft-bodied creatures whose existence has been chronicled in varied locations across the face of the earth, including paleontological treasure troves in China, Australia and western Canada.
By the dawning of the Ordovician, 485 million years ago, trilobites such as Isotelus latus still represented the dominant form of life on earth, but that dominance was beginning to be threatened by the emergence of primitive fish. By the end of the period, some sea creatures had become bold enough to venture onto land, beginning to inhabit the fringes of the continental mass known as Gondwana. Yet disaster loomed, as the planet's first major extinction event at the end of the Ordovician eradicated virtually all of this terrestrial life… and severely depleted life in the seas, as well.
The Silurian began 443 million years ago and witnessed a rejuvenation of life following this mass extinction. Trilobites, while in decline, still produced species like Arctinurus boltoni, and continued to thrive in the world's oceans where they were joined by an ever-growing variety of fish, as well as by various species of eurypterids. Life returned to the land where plants began to dominate the landscape. At this time, four distinct continents existed on the planet, providing ample new environments for life forms to emerge and evolve.
By 419 million years ago, the Devonian was underway, a time when huge, armor-plated fish roamed the seas, posing a further threat to the remaining trilobites such as Drotops armatus … as well as to everything else that crossed their path. Plants continued to monopolize the land, helping to develop a more hospitable, oxygen-filled environment for terrestrial life to flourish. But once again earth proved to be a fickle host when the planet's second great extinction eradicated 70 percent of all life… an event that emphatically signaled the end of the Devonian.
During the Mississippian and Pennsylvanian periods (commonly combined into the Carboniferous), which began 359 million years ago, the planet's temperature rose dramatically, creating lush tropical swamps that pervaded virtually every land mass. It was the ideal environment for certain early tree species to flourish -- which they did, eventually leaving behind the coal-rich deposits that provide the Carboniferous with its name. The seas were also particularly warm, often forcing such diminutive trilobite species as Comptonaspis swallowi to burrow into the surrounding sea floor sediments for safety.
By the beginning of the Permian, 299 million years ago, all the earth's landmasses had once again come together to form the supercontinent called Pangea. The few remaining trilobites were uniformly small in size and played a relatively insignificant role in life's continuing evolution… all of which came to a crashing halt when the greatest mass extinction in earth's history wiped out 90 percent of all life on the planet, subsequently putting a dramatic end to both the Paleozoic Era and the trilobite's 270 million year swim through Deep Time.