Trilobite Website

Trilobites were among the first dominant multicellular lifeforms to inhabit our planet’s seas. 

The Trilobita, an extinct class of Paleozoic marine arthropods, was made up of 10 orders, over 150 families, about 5,000 genera and over 22,000 described species. They initially emerged in the Lower Cambrian, some 521 million years ago, and survived until the end of the Permian, 270 million years later.

They had calcite-covered bodies that were divided into three parts: a head (or cephalon), a midsection (or thorax), and a tail (or pygidium). They could grow to more than two feet in length, though most species were only two or three inches long. But what makes them particularly interesting to both academicians and collectors, is that they were a primary component of the famed Cambrian Explosion that started approximately 540 million years ago. That’s when the early oceans first began bursting with organic life.

Some 20 million years later—which is a mere “blip” in geologic time—trilobites dominated those seas. By that time, they already possessed not only hard outer shells, but also complex eyes, main pairs of walking legs, and an egg-laying reproductive system. They were perhaps the first animals ever to display some of these morphologic traits, all of which helped them become essential and highly successful components of those ancient seas. The Gallery of Trilobites showcases these traits over these vast periods of time and from specimens collected from almost every corner of the planet.

Cambrian Period (542-488 million years ago)

The dawning of the Cambrian Period corresponded in near-perfect synchronicity with the emergence of multicellular life on Earth. Trilobites served as the key index fossils of the entire Paleozoic Era, arising in the Lower Cambrian, 521 million years ago, and lasting until the end of the Permian, some 270 million years later.

Only a few million years after their initial appearance, trilobites were already thriving within those primeval oceans, with thousands of distinct species filling virtually every available ecological niche within the planet’s diverse marine habitats. But these amazing arthropods were far from the only creatures living in those early seas. In the Cambrian, a time when oceans dominated the globe and surrounded Southern Hemisphere supercontinents like Laurentia and Amazonia, such trilobite species as Bathyuriscus fimbriatus,Wutingaspis tingi, Orygmaspis morrisi, and Olenellus cordillerae were joined by a plethora of other invertebrates. Many of these were non-biomineralized creatures whose soft-bodied existence has been chronicled in varied locations across the face of the Earth, including paleontological treasure troves in China, Australia, and western Canada.

The Cambrian abruptly ended with a major extinction event. In the wake of that episode, which was possibly triggered by a pronounced drop in marine oxygen levels, 60 percent of extant ocean life–including many trilobite genera, in addition to entire orders of brachiopods, conodonts, and soft-bodied arthropods–forever disappeared from the Paleozoic scene.

Ordovician Period (488-444 million years ago)

Soon after the dawning of the Ordovician Period, trilobites reached what some academics now consider their evolutionary peak, producing thousands of new species, including Isotelus latus, Parisoceraurus rectangulatus, and Amphilichas ottawaensis.

Some 36 million years into their incredibly successful swim through the Paleozoic Era, these highly adaptable arthropods clearly remained one of the world’s dominant forms of marine life. But that dominance was beginning to be threatened by the emergence of an ever-increasing army of predators, including giant cephalopods and primitive jawed fishes.

Much of what would eventually emerge as North America and Europe was then covered by warm, shallow seas, a fact that allowed trilobites to eventually become fossilized in locations now hundreds of kilometers from the nearest body of salt water. By the end of that period, some marine creatures had become bold enough to venture permanently onto land, beginning to inhabit the fringes of the continental mass known as Gondwana. Things seemed to be evolving at a sprightly pace both in sea and on land.

Yet disaster loomed again, as the planet’s second major extinction event at the end of the Ordovician–possibly generated by rapid global cooling–eradicated virtually all terrestrial organisms and severely depleted life in the oceans as well. 

Silurian Period (444-416 million years ago)

The Silurian Period began 444 million years ago, characterized by a rejuvenation of planetary life following the mass extinction that had occurred at the end of the Ordovician.

With a duration of “only” 25 million years, this was the shortest, and perhaps least extraordinary of the various Paleozoic periods. The Silurian was a period marked most notably by global climatic stabilization and a significant rise, then fall, in worldwide sea levels.

Trilobites, while continuing the inexorable decline that had begun after their generic peak in the Lower Ordovician, still produced thousands of strikingly diverse new species. These included the likes of Arctinurus boltoni, Aanasobella asper, and Metopolichas breviceps, each of which displayed the ever-increasing degree of morphological complexity that these arthropods were forced to assume merely to survive within their chosen marine ecosystems.

As this frequently spectacular array of trilobites continued to thrive within the Earth’s oceans, which then included the Iapetus and Panthalassic, they were joined by an ever-growing assembly of fishes, as well as by various species of eurypterids, some of which served among the apex predators of the Silurian.

After a series of unsuccessful early attempts, life returned to the land where plants began to dominate the global terrain. At this moment in primal time, four distinct continents existed on the planet. These and their surrounding waters provided ample new ecological environments in which diverse lifeforms, including trilobites, could continue to emerge and evolve. 

Devonian Period (416-359 million years ago)

By 419 million years ago, the Devonian was underway, a period when huge, armor-plated fishes, some up to 9 meters in length, first roamed the seas.

These imposing creatures posed a further evolutionary hurdle to the remaining trilobites, which then included the likes of Huntoniatonia huntonensis, Dicranurus monstrosus and Belenopyge balliviani. The Devonian’s cast of giant predators, which also featured terrorizing sea scorpions and jet-propelled cephalopods, even threatened trilobite species, such as the spike-covered Drotops armatus, that had emerged specifically to combat these lurking marine menaces.

Though in sharp decline, trilobites continued to produce morphologically more complex species, many featuring an intriguing and often intimidating assortment of flowing spines, pointed barbs and imposing rostrums, each of which seemingly served a vital function in the animal’s ability to swim, crawl, feed, defend itself, or reproduce. Trilobite eyes, as shown on species such as Eldredgeops milleri, also reached their apex during the Devonian, frequently appearing atop the trilobite’s rounded cephalon as huge, compound ocular outlets covered by hundreds of perfectly formed, geometrically interconnecting lenses.

During this period, plants continued to spread on land, helping to develop a more hospitable, oxygen-filled environment that allowed terrestrial life to slowly begin flourishing. But once again Earth proved a fickle host when the planet’s next great extinction event served to eradicate 70 percent of life around the globe—a disaster that emphatically and dramatically signaled the end of the Devonian.

Carboniferous Period (359-299 million years ago)

The Carboniferous Period, commonly separated into the Mississippian and Pennsylvanian within North American paleontological circles, began 359 million years ago following the massive environmental changes and corresponding habitat destruction that marked the end of the preceding Devonian.

During this time, global temperatures rose dramatically, creating lush tropical swamps that pervaded the planet’s equator-hugging landmasses. By now, trilobites were barely hanging on within their chosen marine ecosystems, continuing their slow-yet-steady descent towards evolutionary oblivion. And though this late-stage Paleozoic world may not have provided ideal conditions for trilobite continuity, it did supply a near-perfect environment for certain early plant species to flourish, which they did, eventually leaving behind the coal-rich deposits that provide the Carboniferous with its name.

The period’s oceans were also particularly warm, often forcing such diminutive trilobites as Ameura major, Cummingella belisama, and Comptonaspis swallowi— each a member of the Proetida order, which by the dawning of the Mississippian contained all remaining trilobite species—to continually burrow into the surrounding sea floor sediments to escape both the escalating water temperatures and an ever-more aggressive cast of predators, including early sharks and amphibians.

By the beginning of the Permian, 299 million years ago, all the Earth’s landmasses had once again joined together to form the supercontinent called Pangea. The few remaining trilobite species that lived amid the coastal plateaus which surrounded this huge landmass were uniformly small, under 6 centimeters (2.3 inches) in length.

Permian Period (299-251 million years ago)

It is the considered opinion of many trilobite enthusiasts that Permian specimens of these intriguing invertebrates rank among the most coveted of all Paleozoic prizes. The fact is that even the most extensive, expansive, and expensive of fossil assemblages may perhaps feature only one or two such trilobites, and these will rarely be complete. Indeed, the limited arthropod material available from that long-distant period of Earth history provides compelling evidence that by the time the Permian began some 299 million years ago, trilobites were struggling to survive within their constantly changing marine world. Their average size had shrunk to only a few centimeters, and their speciation had reached a critical low.

Yet despite all such apparent adversity, the fossilized distribution of species such as Ditomopyge artinskiensis, Neoproetus indicus, and Acropyge multisegmenta is still rather impressive. The often disarticulated, or tightly enrolled, remains of these terminal trilobites can be found within sedimentary layers in such currently far-flung locations as Hungary, Timor, China, Iran, Pakistan, Russia, and Japan.

In the Permian, all of Earth’s landmasses had once again joined together to form the supercontinent called Pangea. The remaining trilobite species that lived amid the coastal plateaus and shallow marine reefs that surrounded the central equatorial edges of this huge landmass played a rather insignificant role in Earth’s continued faunal expansion, that by then included the terrestrial emergence of two distinct groups of reptiles.

Yet whether the heterogeneity of the planet’s animal population was accelerating on land or beneath the waves, virtually all such evolutionary advancement came to a crashing halt some 252 million years ago. It was then that the greatest mass extinction event in Earth’s history, perhaps caused by a string of volcanoes erupting in what is now Siberia or by a series of huge, iron-nickel meteorites striking the planet’s surface, wiped out 90 percent of life around the globe, consequently bringing a dramatic close to both the Paleozoic Era and the trilobites’ 270-million-year swim through Deep Time.