As you peruse the trilobite specimens adorning this site, the temptation may well be to envision these ancestral arthropods as solitary creatures… proud denizens of the world's deep-time seas, captured for eternity as they proceeded stoically and individually about their daily routine. After all, the vast majority of our pictured examples are of singular specimens, many rather aesthetically posed amid a matrix field comprised of half a billion year old primordial ooze-turned-to-stone.
The fact of the matter is, however, that certain aspects of trilobite behavior may not be exactly as we imagined; indeed, they may be quite the opposite. As paleontologists have recently begun to learn, it seems that rather than being isolated “loners”, many trilobites were highly communal animals, often living in tightly packed groups, perhaps even traversing the world's seas in long single-file, cephalon-to-pygidia lines. This was apparently a lifestyle that provided both safety in numbers and markedly increased each trilobite's procreative opportunities.
In fact, in some cases, particularly those trilobites found in sedimentary outcrops in such now-diverse locations as Oklahoma, the Czech Republic, Russia, Morocco, Utah and British Columbia, these ancient creatures were nothing less than pervasive within their given ecosystem. In these locales (as well as in an ever-increasing number of sites world-wide) layers of Paleozoic rock have been found that are literally covered in trilobites.
A number of scientists believe that these mass mortality assemblages, such as those exhibited by the Ordovician asaphid Homotelus bromidensis, may reflect the end result of an oceanic tidal estuary draining or evaporating, leaving its inhabitants quite literally high-and-dry. Others state that some trilobites, such as the Devonian phacopid Eldredgeops milleri, may have followed a life cycle that would have drawn their species together in prolific numbers at certain times of the year to create mating assemblages. The net effect of such actions may well have left ancient sea floors carpeted with complete trilobite carapaces. Another scientific thought postulates that large numbers of the same trilobite species may have continually lived in close proximity, sharing a particularly hospitable ecological niche for protection and best utilization of resources.
One interesting theory that has gained traction in recent years states that trilobites found in the same geologic horizon may have lived in numbers somewhat akin to the predator/prey ratios we see in the wild today. Anyone who has ever viewed a Nat Geo special on the African savannas knows that prey animals like zebras and wildebeest clearly outnumber the lions and leopards that pursue them. Some 500 million years ago, during the Cambrian, a similar situation may have existed between the possibly predatory trilobite Olenoides superbus (an uncommon find) and the pervasive Elrathia kingii (numbering in the thousands) that they might have fed upon.
The bottom line is that while trilobites represent relatively rare remnants of an incredibly distant time, as we continue to further explore the sedimentary rocks that comprise the earth's surface, we find that their remains are actually quite ubiquitous. Indeed, through the occasionally pervasive manner of their fossilization, trilobites are beginning to reveal tantalizing bits of information concerning their lifestyles in those ancient seas, hundreds of millions of years in the past.
Here are some mass mortality trilobite plates from around the world:
Eldredgeops milleri: These Devonian phacopids may have been drawn together in mating assemblages.
Homotelus bromidensis: Entire Ordovician layers in Oklahoma are covered in the fossilized remains of these 2 inch trilobites.
Flexicalymene senaria: Dozens of these Canadian trilobites are seen here in association with Ceraurus pleuexanthemus.
Conocoryphe sulzuri: These blind Cambrian trilobites found in the Czech Republic may have gathered together for protection.
Kootenia youngorum: This is the only known example of this rare species from the Cambrian of Utah displaying communal behavior.
Pseudomegalaspis patagiata: Here are both complete and disarticulated examples of this Ordovician species found in Sweden.
Examples of the Polish trilobite Trimerocephalus caecus often provide evidence of trilobites "lining up" in single files while traveling across the sea floor.
Elrathia kingii: Perhaps the most common trilobite in the world, this Cambrian species is often found in mass mortality plates.