Trilobite Relatives: Soft Bodied Arthropods

     More than half a billion years ago, on temperate oceanic plateaus located around the globe, a legion of strange creatures waged a continual battle for survival. They possessed neither the hard outer shells of their trilobite cousins nor the size or strength to assure their continued existence. Indeed, life may have been short and not-particularly-sweet for these primitive sea-dwelling inhabitants. 
      One can imagine the tenuous times led by these ancient soft bodied arthropods, playing hide-and-seek with predators as they darted in and out of sponge beds and under swaying eocrinoid stems in their attempts to simply make it through one more day. Some made it...some didn't. And even those that managed to survive attacks by the mud-dwelling carnivorous worm known as Ottoia or the fast-swimming predatory giant called Anomalocaris may have still suffered a disastrous fate. 
       The Middle Cambrian was a time of great instability on a fast-changing planet, and underground volcanic eruptions and major earthquake activity may well have been a routine fact-of-life for the inhabitants of the earth's primeval seas. Indeed, the threat of sub-oceanic seismic activity and habitat-destroying landslides may have presented a far greater challenge to these minute and apparently fragile creatures than all the era's predators put together. Alas, how exasperating it must have been to spend the vast majority of your short existence escaping from sharp-fanged sea monsters, only to be done in by a rampaging pile of mud. 
       In retrospect, however, that mud was far more than merely an inconvenience to the local inhabitants. Without it our knowledge of the planet's primitive seas -- and of its amazingly diverse invertebrate fauna -- would be severely limited. Current scientific thought postulates that a vast majority of the soft bodied specimens that we now know of through the fossilization process in present-day locations as diverse as British Columbia, China and Australia, were at one time or another buried by mudslides -- underwater avalanches that quickly covered everything in their vicinity. 
     By doing their dirty work so quickly and effectively, these landslides often served as natural time capsules, burying nearly the complete ecosystem within their path of destruction. How lucky for anyone fascinated by the earth's primitive past that such "accidents" of nature occurred. Without them, the complex jigsaw puzzle that is our planet's earliest history would be lacking some of its most critical edge pieces -- most notably, evidence of such creatures as Marrella, similar to a lace-crab; Aysheia, a lobe-limbed "caterpillar"; and Hallucigenia, a bizarre multi-spined creature that still remains a mystery to science.
     Thanks to the on-going efforts of scientific crews searching for Cambrian-age soft bodied material in outposts like Canada's famed Burgess Shale, China's Chengjaing lagerstatte, the western US's Wheeler Shale and Australia's Emu Bay formation, some of the key questions surrounding the earth's first inhabitants are now beginning to be answered. However, there are still many more riddles surrounding these enigmatic soft bodied creatures, and those are likely to remain -- at least until some intrepid paleontologist stumbles upon the next key to further unlocking this timeless story of mystery and intrigue. 
Here is a look at some of the soft bodied creatures that shared the Paleozoic seas with trilobites:

Trilobite fossil embedded in rock.

Marella splendens