The First Trilobites
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 as Spriggina floundersi -- 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 as Profallotaspis and Bigotina appear 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 of Gabriellus kierorum, Bristolia bristolensis and Olenellus fremonti would soon help to firmly establish a class of animals that would survive for the next 270 million years.
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: An elegant 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.